1,185 entries
Acronyms and short forms across networking, data centres, cloud, security, operations and regulation.
Glossary
Every acronym, spelled out
Networking, data centres, cloud, security and regulation all have their own shorthand. Here are the acronyms and terms used on this site, with what each stands for and a plain line on what it does. Most also link to the page where I cover it.
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1,185 terms, in plain English
Type part of an acronym or a word from its meaning, such as BGP, tunnel or resilience. Each entry says what the letters stand for and what it does in one line. Most also link to the page where I explain it. Where the same letters mean two different things, each meaning has its own entry and its own links.
Showing all 1,185 terms.
A to E
Terms from A to E
Numbers
- 10GBASE / 25GBASE / 100GBASE / 400GBASE
- IEEE Ethernet Physical Layer Naming, for Example 400GBASE-DR4Speed, BASE for baseband, then reach and lane code.
- 16GFC / 32GFC / 64GFC
- Fibre Channel Speed Generations16, 32 and 64 Gb/s Fibre Channel.
- 2N / N+1 / 2N+1
- Redundancy LevelsTwo full systems / one spare unit / two systems plus a spare.
- 400ZR / ZR+
- 400G coherent ZR Optic (and its longer reach variants)OIF standard pluggable DWDM optic, up to about 120 km; ZR+ goes further.
- 802.1ad
- IEEE Provider Bridging (QinQ)Double VLAN tagging; outer TPID 0x88A8.On this site: WAN, MPLS and VPN
- 802.1AE
- IEEE MACsec StandardLine rate layer 2 encryption.On this site: Security fundamentals, WAN, MPLS and VPN
- 802.1AX / 802.3ad
- IEEE Link Aggregation StandardsLACP; 802.3ad was the original, now 802.1AX.
- 802.1p
- IEEE Priority TaggingThe 3 bit CoS value in the 802.1Q tag.
- 802.1Q
- IEEE VLAN Tagging StandardAdds a 4 byte tag with a 12 bit VLAN ID to Ethernet frames on trunks.On this site: Networking fundamentals, Security fundamentals, Servers and virtualisation
- 802.1Qbb / 802.1Qaz
- IEEE Priority Flow Control / Enhanced Transmission SelectionThe DCB standards behind lossless RoCE.
- 802.1X
- IEEE Port Based Network Access ControlAuthenticates devices before they join the network, using RADIUS.On this site: SD-Access campus fabric, Government and defence, IoT and edge
A
- A, AAAA, CNAME, MX, NS, PTR, SRV
- DNS Record Types: Address, IPv6 address, Canonical Name, Mail Exchanger, Name Server, Pointer, ServicePTR records make logs and traceroutes readable; SRV records locate services such as Active Directory.
- A1
- ASHRAE Equipment Class A1Allowable inlet range 15 to 32 °C; recommended 18 to 27 °C.On this site: Data centre facilities
- A100 / H100 / H200 / B200 / B300 / GB200 / GB300
- NVIDIA GPU and Superchip Model NamesSuccessive NVIDIA data centre GPU generations; GB models pair Grace CPUs with Blackwell GPUs.
- AAA
- Authentication, Authorisation and AccountingWho you are, what you may do, and a record of what you did.On this site: SD-Access campus fabric, SD-WAN and SDN, Security fundamentals
- AAEP
- Attachable Access Entity ProfileACI object that ties interface policies to VLAN pools and domains.On this site: VXLAN EVPN and ACI
- AAP
- Ansible Automation PlatformRed Hat's supported, scaled Ansible with RBAC and audit.On this site: Troubleshooting
- ABR
- Area Border RouterOSPF router joining area 0 to another area; where summaries are made.On this site: Routing protocols, Troubleshooting
- AC / DC (power)
- Alternating Current / Direct CurrentPSUs turn AC to DC; some hyperscale racks use a DC busbar.
- ACI
- Application Centric InfrastructureCisco controller driven fabric.On this site: VXLAN EVPN and ACI, Data centre networks, Design authority
- ACK / SYN
- Acknowledge / SynchroniseTCP flags in the three way handshake.
- ACL
- Access Control ListOrdered permit and deny rules; implicit deny at the end.On this site: AWS, Azure and Google Cloud, VXLAN EVPN and ACI, Data centre networks
- ACME
- Automatic Certificate Management EnvironmentProtocol for automated certificate issuance and renewal.On this site: Security fundamentals, Troubleshooting
- AD
- Active DirectoryMicrosoft directory that ISE and AAA servers check users against. Also Administrative Distance.On this site: Servers and virtualisation
- AD
- Administrative DistanceCisco trust value for route sources: lower wins. Also Active Directory.On this site: Routing protocols, Troubleshooting
- AD / LDAP / LDAPS
- Active Directory / Lightweight Directory Access Protocol (over TLS)Directory services behind identity for infrastructure access.
- ADM
- Architecture Development MethodTOGAF's cycle for building architecture; useful shared vocabulary in design authority forums.On this site: Design authority
- ADP
- Aruba Discovery ProtocolAruba access points use it to find a controller on the local subnet.On this site: Wireless and mobile
- ADR
- Architecture Decision RecordA short record of one design decision, its options and consequences; the design authority's memory.On this site: Design authority
- AED
- Authoritative Edge DeviceOTV edge that forwards a given VLAN for a site.On this site: Data centre networks
- AES
- Advanced Encryption StandardStandard symmetric cipher for IPsec, SSH and SNMPv3 privacy.On this site: Networking fundamentals, Security fundamentals, Security
- AES / GCM
- Advanced Encryption Standard / Galois Counter ModeThe cipher and mode used by MACsec and TLS.
- AES-256
- Advanced Encryption Standard, 256 bit KeyStrong symmetric encryption for data at rest and in transit.On this site: Security fundamentals, Security, WAN, MPLS and VPN
- AF
- Assured ForwardingDSCP classes AF11 to AF43; the second digit is drop priority. Also BGP Address Family.On this site: Switching and campus LAN
- AF41
- Assured Forwarding Class 4, low DropDSCP 34, used for interactive video.On this site: Switching and campus LAN, WAN, MPLS and VPN, Wireless and mobile
- AFC
- Automated Frequency CoordinationDatabase service that clears 6 GHz Wi-Fi access points to transmit at standard power without interfering with fixed links.On this site: Wireless and mobile
- AFI / SAFI
- Address Family Identifier / Subsequent Address Family IdentifierMP-BGP labels; L2VPN EVPN is AFI 25, SAFI 70.
- AH
- Authentication HeaderIPsec integrity without encryption (IP protocol 51); rarely used.On this site: Security fundamentals
- AHV
- Acropolis HypervisorNutanix's KVM based hypervisor, one VMware alternative.On this site: Private cloud and storage, Servers and virtualisation
- AI
- Artificial IntelligenceSoftware that learns patterns from data to classify, predict or generate content.On this site: Data centre networks, Networking fundamentals, Servers and virtualisation
- AI / ML
- Artificial Intelligence / Machine LearningModels trained on data; on this site, mostly the GPU clusters and networks that train and serve them.
- AIOps
- AI for IT OperationsUses analytics and ML on telemetry to spot and correlate faults.
- AKS
- Azure Kubernetes ServiceMicrosoft's managed Kubernetes, where Azure runs the control plane.On this site: AWS, Azure and Google Cloud
- ALB
- Advanced Load Balancer (NSX Advanced Load Balancer)Avi based load balancer, now VMware Avi Load Balancer; licensed separately.
- ALB
- Application Load BalancerAWS layer 7 load balancer for HTTP and HTTPS that routes by host name and path.On this site: Load balancing, AWS, Azure and Google Cloud
- ALG
- Application Layer GatewayFirewall helper that understands a protocol, such as FTP or voice signalling, and opens the right ports.On this site: Firewall platforms, Networking fundamentals, Troubleshooting
- AMD
- Advanced Micro DevicesCPU (EPYC) and GPU vendor, and maker of Pensando DPUs.On this site: Servers and virtualisation
- AMQP
- Advanced Message Queuing ProtocolOpen messaging protocol for queues between applications, used by RabbitMQ and Azure Service Bus.On this site: IoT and edge
- ANA
- Asymmetric Namespace AccessNVMe multipathing that tells hosts which paths are optimised.
- ANC
- Adaptive Network ControlCisco ISE action that quarantines or shuts an endpoint's port on demand, through change of authorisation.On this site: Troubleshooting
- AOC
- Active Optical CableFibre cable with fixed optics on each end, for runs of tens of metres.On this site: Data centre facilities
- APC / UPC
- Angled Physical Contact / Ultra Physical ContactFibre connector polish types; never mix them on one link.
- APD
- All Paths DownvSphere state where a host loses every path to a storage device and cannot tell if it will return.On this site: Servers and virtualisation
- API
- Application Programming InterfaceHow tools and scripts drive NSX, FMC, Panorama and FortiManager.On this site: Load balancing, Network automation, VXLAN EVPN and ACI
- APIC
- Application Policy Infrastructure ControllerThe ACI controller cluster, usually three nodes.On this site: Network automation, VXLAN EVPN and ACI, Private cloud and storage
- APIPA
- Automatic Private IP AddressingWindows gives itself a 169.254.x.x address when no DHCP server answers, a sure sign DHCP has failed.On this site: Troubleshooting
- APN
- Access Point NameTells a mobile network which data network and settings a SIM connects to, such as a private APN for IoT.On this site: IoT and edge
- App-ID
- Application Identification (Palo Alto)Identifies the application regardless of port.On this site: Firewall platforms, Support and service management, Troubleshooting
- ARB
- Architecture Review BoardForum that reviews and approves designs.On this site: Design authority
- ARM
- Arm Architecture (originally Advanced RISC Machines)Low power CPU architecture, now in some servers and NVIDIA Grace CPUs.On this site: AWS, Azure and Google Cloud
- ARM
- Azure Resource ManagerThe Azure deployment and management layer, and the template language that drives it.On this site: AWS, Azure and Google Cloud
- ARP
- Address Resolution ProtocolFinds the MAC for an IPv4 address on the local subnet; spoofing is stopped by DAI.On this site: Load balancing, SD-Access campus fabric, VXLAN EVPN and ACI
- AS
- Autonomous SystemA network under one routing policy, identified by an ASN.On this site: Cloud architecture, VXLAN EVPN and ACI, Data centre networks
- ASA
- Adaptive Security ApplianceCisco stateful firewall and VPN platform.On this site: Firewall platforms, Networking fundamentals, Security fundamentals
- ASAv
- Adaptive Security Appliance VirtualOfficial name Cisco Secure Firewall ASA Virtual.On this site: Firewall platforms, Troubleshooting
- ASBR
- Autonomous System Boundary RouterRouter that injects external routes into OSPF.On this site: Routing protocols, Troubleshooting
- ASDM
- Adaptive Security Device ManagerGUI for managing an ASA.On this site: Firewall platforms
- ASHRAE
- American Society of Heating, Refrigerating and Air Conditioning EngineersIts TC 9.9 committee sets the recommended server inlet range of 18 to 27 °C.On this site: Data centre facilities
- ASIC
- Application Specific Integrated CircuitForwarding chip in switches and firewalls.On this site: VXLAN EVPN and ACI, Troubleshooting
- ASM
- Application Security ManagerThe web application firewall module on F5 BIG-IP.On this site: Load balancing
- ASN
- Autonomous System NumberBGP identifier; private ranges 64512 to 65534 and 4200000000 to 4294967294.On this site: Data centre networks
- ASP
- Accelerated Security PathASA data path; show asp drop lists why packets were dropped.On this site: Firewall platforms, Troubleshooting
- ASR
- Aggregation Services RouterCisco WAN edge and provider router family; the ASR 1000 can also run OTV.
- ATS
- Automatic Transfer SwitchMoves load between mains and generator in seconds.On this site: Data centre facilities, Troubleshooting
- AV
- Audio VisualMeeting room screens, cameras and speakers, often on their own VLAN with multicast.On this site: IoT and edge, Operational technology
- AVF
- Active Virtual ForwarderGLBP router that forwards for one of the virtual MACs.On this site: Switching and campus LAN
- AVG
- Active Virtual GatewayGLBP router that answers ARP and hands out virtual MACs.On this site: Switching and campus LAN
- AWS
- Amazon Web ServicesPublic cloud provider.On this site: Load balancing, SD-Access campus fabric, IoT and edge
B
- BA
- Bridge AssuranceNexus feature, on by default on network ports: the port blocks if BPDUs stop.
- BACnet
- Building Automation and Control NetworksBuilding systems protocol (BACnet/IP); BMS networks must be segmented as OT.On this site: SD-Access campus fabric, Data centre facilities, IoT and edge
- BAU
- Business As UsualDay to day running of the live service, as opposed to project or change work.
- BBMD
- BACnet Broadcast Management DeviceForwards BACnet broadcasts between IP subnets so building controllers can find each other.On this site: IoT and edge, Troubleshooting
- BD
- Bridge DomainACI layer 2 forwarding domain inside a VRF.
- BDR
- Backup Designated RouterOSPF standby for the DR on a broadcast segment.On this site: Routing protocols
- BFD
- Bidirectional Forwarding DetectionSub second failure detection for BGP, OSPF and NSX Tier-0 peers.On this site: VXLAN EVPN and ACI, Data centre networks, Design authority
- BGP
- Border Gateway ProtocolPath vector protocol on TCP 179; WAN edges and the NSX Tier-0 uplinks.On this site: Network automation, SD-Access campus fabric, AWS, Azure and Google Cloud
- BGW
- Border GatewaySite edge node in VXLAN EVPN Multi-Site designs.On this site: Troubleshooting
- BI
- Business IntelligenceReporting and analytics workloads that run on big data pods.
- BID
- Bridge IDPriority plus MAC address; the lowest becomes the spanning tree root.
- BiDi
- Bidirectional OpticSends and receives on two wavelengths over one fibre pair or strand to reuse existing cabling.
- BIOS
- Basic Input Output SystemFirmware that starts a server before the operating system; now mostly replaced by UEFI.On this site: Servers and virtualisation
- BIOS / UEFI
- Basic Input/Output System / Unified Extensible Firmware InterfaceServer firmware; UEFI supports secure boot and HTTP boot.
- BL / SL
- Border Leaf / Service LeafLeaf roles: external connectivity / firewalls, load balancers and shared services.
- BLE
- Bluetooth Low EnergyLow power Bluetooth for sensors, beacons and asset tags.On this site: IoT and edge
- BMC
- Baseboard Management ControllerOut of band server management chip; keep it on the OOB network.On this site: AI infrastructure, Data centre facilities, Design authority
- BMS
- Building Management SystemMonitors and controls cooling, power, fire and leaks.On this site: AI infrastructure, Data centre facilities, Operational technology
- BOM
- Bill of MaterialsItemised hardware, software, optics and cabling per pod type; drives unit cost and procurement.On this site: Data centre facilities
- BPDU
- Bridge Protocol Data UnitSpanning tree messages; BPDU Guard shuts edge ports that receive them.On this site: Data centre networks, Security fundamentals, Troubleshooting
- BPF
- Berkeley Packet FilterCapture filter syntax used by tcpdump and Wireshark capture filters.On this site: Troubleshooting
- BPSS
- Baseline Personnel Security StandardThe entry level UK government staff check: identity, right to work, employment history and unspent convictions.On this site: Government and defence
- BS / EN
- British Standard / European NormFor example BS EN 50600 (data centres) and BS EN 50174 2 (cabling separation).
- BSD
- Berkeley Software DistributionUnix family that Sidewinder's hardened operating system is based on.
- BSL
- Business Source LicenseTerraform's licence since 2023; OpenTofu is the open source fork.
- BSR
- Bootstrap RouterElects and advertises the PIM rendezvous points for multicast groups across a domain.On this site: Routing protocols
- BSS
- Basic Service SetOne access point and the clients joined to it, identified by its BSSID.On this site: Wireless and mobile
- BSS
- Business Support SystemsTelecoms systems for orders, billing and customer accounts; the partner of OSS.On this site: Network automation
- BTU
- British Thermal UnitHeat unit; 1 kW is about 3,412 BTU per hour.On this site: Data centre facilities
- BUM
- Broadcast, Unknown Unicast and MulticastTraffic that is flooded; overlays such as NSX and VXLAN must replicate it.On this site: Troubleshooting
- BYOD
- Bring Your Own DeviceStaff use their own phones and laptops, usually on a separate network with limited access.On this site: SD-Access campus fabric, Security
C
- C13 / C14 / C19 / C20
- IEC 60320 power Connector TypesC13/C14 for 10 A loads; C19/C20 for 16 A high power servers.
- CA
- Certificate AuthorityIssues and signs certificates in a PKI. Also ITIL change authority.On this site: IoT and edge, Security fundamentals, Security
- CAB
- Change Advisory BoardReviews normal changes for risk, impact and timing; bring a clear plan with rollback.On this site: Design authority, Firewall platforms, Support and service management
- CAC / HAC
- Cold Aisle Containment / Hot Aisle ContainmentStops hot and cold air mixing; hot aisle preferred for new builds.
- CAF
- Cyber Assessment FrameworkNCSC framework of 14 principles used to assess operators of essential services.On this site: Government and defence
- CAK
- Connectivity Association KeyMACsec root key shared by both ends.On this site: Security fundamentals
- CAM
- Content Addressable MemoryHardware table where a switch holds learned MAC addresses.On this site: Switching and campus LAN
- CapEx
- Capital ExpenditureUp front spend on hardware and build.
- CAPWAP
- Control and Provisioning of Wireless Access PointsTunnels control and client traffic between a lightweight access point and its controller, on UDP 5246 and 5247.On this site: SD-Access campus fabric, Troubleshooting, Wireless and mobile
- CASB
- Cloud Access Security BrokerSees and controls how staff use cloud apps, such as blocking uploads to personal storage.On this site: SD-WAN and SDN
- Cat6A
- Category 6A twisted PairCopper cabling for 10GBASE-T and management ports.
- CBWFQ
- Class Based Weighted Fair QueuingGuarantees bandwidth per traffic class on a congested link.On this site: Routing protocols, WAN, MPLS and VPN
- CCDP
- Cisco Certified Design ProfessionalYou hold it (ARCH)On this site: VXLAN EVPN and ACI, Data centre networks, IP addressing and subnetting
- CCI
- Co Channel InterferenceAccess points on the same channel hear each other and take turns, so capacity drops.On this site: Troubleshooting
- CCIE
- Cisco Certified Internetwork ExpertYou passed the R&S and Security written exams only; say written, lab not attempted.On this site: Load balancing, Firewall platforms, Government and defence
- CCIP
- Cisco Certified Internetwork ProfessionalLegacy service provider certification you hold.On this site: Home lab
- CCKM
- Cisco Centralised Key ManagementCisco fast roaming method that caches keys, so clients skip a full 802.1X exchange when they move.On this site: Wireless and mobile
- CCNA
- Cisco Certified Network AssociateYou hold it.On this site: IP addressing and subnetting, Networking fundamentals, Switching and campus LAN
- CCNP
- Cisco Certified Network ProfessionalYou hold CCNP Enterprise and CCNP R&S.On this site: Load balancing, Network automation, SD-Access campus fabric
- CCP
- Central Control PlaneRuns in the NSX Manager cluster; computes and pushes runtime state to hosts.On this site: Troubleshooting
- CCTV
- Closed Circuit TelevisionPhysical security monitoring of data halls and cages.On this site: Data centre facilities
- CCVP
- Cisco Certified Voice ProfessionalLegacy voice certification you hold.On this site: Home lab
- CDE
- Cardholder Data EnvironmentSystems that store, process or transmit card data plus connected systems; keep it small by segmentation.On this site: Resilience, risk and cost
- CDK
- Cloud Development KitAWS tool that defines infrastructure in a programming language and turns it into CloudFormation.On this site: AWS, Azure and Google Cloud
- CDP
- Cisco Discovery ProtocolShows the device and port at the far end of a link; off at boundaries.On this site: Network automation, SD-Access campus fabric, Networking fundamentals
- CDS
- Cross Domain SolutionAssured gateway for moving data between networks of different classification.
- CDU
- Coolant Distribution UnitHeat exchanger and pumps between facility water and the rack coolant loop.On this site: Data centre facilities
- CE
- Customer EdgeThe customer router that peers with the provider's PE. Also Cyber Essentials.On this site: Home lab
- CEF
- Cisco Express ForwardingCisco's forwarding method using the FIB and adjacency tables.On this site: Routing protocols, Troubleshooting
- CFD
- Computational Fluid DynamicsAirflow modelling of a data hall before build or change.
- CFM
- Cubic Feet per MinuteAirflow unit used to size server and room cooling.On this site: Data centre facilities
- CFS
- Cisco Fabric ServicesSynchronises state between vPC peers over the peer link.On this site: Data centre networks
- CGNAT
- Carrier Grade NATProvider NAT that shares one public IPv4 address across many customers, using 100.64.0.0/10 inside.On this site: WAN, MPLS and VPN
- CHAP
- Challenge Handshake Authentication ProtocolAuthentication used by iSCSI.On this site: Private cloud and storage
- CHW
- Chilled WaterWater from chillers that feeds CRAHs, rear doors and CDUs.
- CI
- Configuration ItemAnything recorded in the CMDB: a switch, firewall, link, VM or service.
- CI/CD
- Continuous Integration / Continuous DeliveryPipelines that test and deploy code, including network as code.
- CIDR
- Classless Inter Domain RoutingPrefix length notation such as /24, replacing the old address classes.On this site: IP addressing and subnetting, Home lab
- CIS
- Center for Internet SecurityPublishes CIS Benchmarks: hardening baselines for Cisco, Palo Alto, Fortinet and others.On this site: Design authority, Government and defence, Security fundamentals
- CISA
- Cybersecurity and Infrastructure Security AgencyUS agency; publishes the KEV catalogue and Emergency Directives such as ED 25 03.On this site: Support and service management
- CISO
- Chief Information Security OfficerSecurity lead.On this site: Security
- CIST
- Common and Internal Spanning TreeThe MST instance 0 tree that joins MST regions to each other and to older spanning tree versions.On this site: Switching and campus LAN, Troubleshooting
- CLI
- Command Line InterfaceWhere 3rd line proves things: show commands, debugs and captures.On this site: Network automation, Troubleshooting, VMware NSX
- CLI / GUI
- Command Line Interface / Graphical User InterfaceManual interfaces that automation should replace for routine change.
- CMDB
- Configuration Management DatabaseRecord of CIs and how they depend on each other; used for impact assessment.On this site: Network automation, Cloud architecture, Data centre networks
- CNA
- Converged Network AdapterServer card carrying Ethernet and FCoE on one port.
- CNAME
- Canonical NameDNS record that makes one name an alias of another.On this site: Networking fundamentals
- CNI
- Container Network InterfacePlugin standard that gives Kubernetes pods networking and network policy.
- CNI
- Critical National InfrastructureAssets the UK depends on.On this site: Government and defence
- CoA
- Change of AuthorisationRADIUS message that lets ISE change or end a session already in place, for example to quarantine a device.On this site: SD-Access campus fabric, IoT and edge, Troubleshooting
- CoAP
- Constrained Application ProtocolLightweight web style protocol over UDP for small IoT devices.On this site: IoT and edge, Networking fundamentals
- COOP
- Council of Oracle ProtocolACI protocol that keeps the spine endpoint database.On this site: VXLAN EVPN and ACI, VMware NSX
- CoPP
- Control Plane PolicingRate limits traffic to the device CPU to protect routing and management.On this site: Routing protocols, Security fundamentals, Security
- CoS
- Class of Service3 bit priority field in the 802.1Q tag.
- CP
- Control PlaneThe part of a system that decides forwarding, such as BGP EVPN.On this site: Troubleshooting
- CPE
- Customer Premises EquipmentProvider owned kit at the site, such as a managed router or network terminating equipment.
- CPNI
- Centre for the Protection of National InfrastructureUK security advice body for critical national infrastructure, renamed NPSA in 2023.On this site: Government and defence
- CPU
- Central Processing UnitGeneral purpose processor; core count drives VMware licence cost.On this site: Load balancing, Troubleshooting
- CR
- Change RequestRaised, approved and recorded in SD+.On this site: Troubleshooting
- CRAC
- Computer Room Air ConditionersRoom cooling units with their own compressors.On this site: Data centre facilities
- CRAC / CRAH
- Computer Room Air Conditioner / Computer Room Air HandlerRoom cooling with its own compressor / with chilled water.
- CRAH
- Computer Room Air HandlersRoom cooling units with fans and coils, fed by chilled water from a central plant.On this site: Data centre facilities
- CRC
- Cyclic Redundancy CheckFrame error check; rising CRC errors point to cabling, optics or duplex faults.On this site: Switching and campus LAN, Troubleshooting
- CRL
- Certificate Revocation ListList of withdrawn certificates that devices check.On this site: Government and defence, Security fundamentals
- CS
- Class SelectorDSCP values CS0 to CS7, kept for compatibility with IP precedence; CS6 for network control.
- CS3
- Class Selector 3DSCP 24, often signalling.On this site: Switching and campus LAN
- CS6
- Class Selector 6DSCP 48, network control.On this site: Switching and campus LAN, WAN, MPLS and VPN
- CSI
- Container Storage InterfacePlugin standard that gives Kubernetes pods persistent storage.On this site: Private cloud and storage
- CSI
- Continual Service ImprovementOngoing improvement of the service.
- CSM
- Cisco Security ManagerCisco tool for managing firewall and VPN policy across many devices.On this site: Firewall platforms
- CSR
- Certificate Signing RequestRequest sent to a CA to issue a certificate.On this site: Security fundamentals
- CSTP
- Co Stop (%CSTP)ESXi esxtop metric: time a multi vCPU VM waits for its vCPUs to be scheduled together.On this site: Servers and virtualisation, Troubleshooting
- CTP
- Critical Third PartyUK regime for direct oversight of key suppliers; first designations July 2026.
- CUCM
- Cisco Unified Communications ManagerCisco call control platform for IP phones and video endpoints.On this site: Home lab
- CUDA
- Compute Unified Device ArchitectureNVIDIA's GPU programming platform; a strong software lock in factor.
- CUE / WUE
- Carbon Usage Effectiveness / Water Usage EffectivenessSustainability metrics alongside PUE.
- CVE
- Common Vulnerabilities and ExposuresUnique ID for each public vulnerability, such as CVE-2025-20333.On this site: Firewall platforms, Support and service management
- CVI
- Cluster Virtual IPThe shared address a Forcepoint firewall cluster answers on, whichever node handles the traffic.On this site: Firewall platforms
- CVSS
- Common Vulnerability Scoring System0 to 10 severity score from FIRST; versions 3.1 and 4.0.On this site: Load balancing, SD-Access campus fabric, SD-WAN and SDN
- CVT
- Cable Validation ToolNVIDIA tool that checks fabric cabling against the planned topology.On this site: AI infrastructure, Private cloud and storage
- CWDM
- Coarse Wavelength Division MultiplexingFew, widely spaced wavelengths; cheaper and shorter reach than DWDM.
D
- DA
- Design AuthorityThe governance forum that reviews and signs off designs against agreed principles.On this site: Troubleshooting
- DAC
- Direct Attach CopperCopper cable with fixed transceiver ends, typically up to about 3 m at 100G and above.On this site: Data centre facilities, Networking fundamentals
- dACL
- Downloadable ACLACL pushed by ISE to a switch port after 802.1X or MAB.On this site: SD-Access campus fabric, Troubleshooting, Wireless and mobile
- DAD
- Duplicate Address DetectionIPv6 check that an address is not already in use before a host takes it.
- DAI
- Dynamic ARP InspectionDrops spoofed ARP using the DHCP snooping binding table.On this site: Networking fundamentals, Security fundamentals
- DAS
- Direct Attached StorageDrives inside or cabled directly to one server.On this site: Servers and virtualisation
- DAVG
- Device Average LatencyESXi esxtop latency at the array and fabric.On this site: Servers and virtualisation
- DB
- DatabaseData platforms such as SQL databases, often a bare metal or VM pod workload.
- dB
- DecibelLog ratio unit for optical and electrical loss; 3 dB is half the power.On this site: Wireless and mobile
- DBD
- Database DescriptionOSPF packet that lists the link state headers each neighbour holds while an adjacency forms.On this site: Routing protocols, Troubleshooting
- dBm
- Decibel MilliwattsAbsolute optical power level; 0 dBm is 1 mW.On this site: Troubleshooting, Wireless and mobile
- DC
- Data CentreThe building or hall that hosts pods.On this site: Troubleshooting
- DCB
- Data Center BridgingIEEE features (PFC, ETS and the DCBX exchange protocol) that make Ethernet lossless for FCoE.
- DCB / DCBX
- Data Center Bridging / DCB ExchangeEthernet extensions (PFC, ETS) for lossless traffic, and their negotiation.
- DCC
- Defence Cyber CertificationUK MOD scheme that certifies suppliers' cyber controls at levels matched to contract risk.On this site: Government and defence
- DCGM
- Data Center GPU ManagerNVIDIA tool for GPU health and telemetry.On this site: AI infrastructure, Troubleshooting
- DCI
- Data Centre InterconnectLinks between data centres; OTV, VXLAN EVPN or DWDM.On this site: Data centre networks, Design authority, Troubleshooting
- DCiE
- Data Centre Infrastructure EfficiencyIT power divided by facility power; the inverse of PUE.On this site: Data centre facilities
- DCIM
- Data Centre Infrastructure ManagementTracks racks, power, space and environment for capacity planning.On this site: AI infrastructure, Network automation, Data centre facilities
- DCNM
- Data Center Network ManagerOlder Cisco Nexus management tool, now Nexus Dashboard Fabric Controller.On this site: VXLAN EVPN and ACI
- DCOM
- Distributed Component Object ModelMicrosoft remote procedure protocol used by older OPC Classic on industrial sites; hard to firewall.On this site: Operational technology, Troubleshooting
- DCP
- Discovery and Basic Configuration ProtocolPROFINET protocol that finds devices and sets their names and IP addresses.On this site: Troubleshooting
- DCQCN
- Data Center Quantized Congestion NotificationECN based congestion control for RoCE.On this site: AI infrastructure, Troubleshooting
- DCS
- Distributed Control SystemProcess plant control with controllers spread across the site and a central operator view.On this site: Operational technology
- DD
- Data Domain (Dell PowerProtect DD)Dell deduplicating backup appliance family.On this site: Networking fundamentals
- DDI
- DNS, DHCP and IPAMThe combined address and name services platform.On this site: Network automation
- DDoS
- Distributed Denial of ServiceFlood from many sources meant to take a service down.On this site: AWS, Azure and Google Cloud, Security fundamentals, Security
- DDR5
- Double Data Rate 5Current server memory generation.On this site: Servers and virtualisation
- DEFCON
- Defence ConditionStandard clauses in MOD contracts; DEFCON 658 covers cyber security.On this site: Government and defence
- DEI
- Drop Eligible IndicatorOne bit in the 802.1Q tag marking frames that can be dropped first under congestion.On this site: Networking fundamentals, Switching and campus LAN
- DES
- Data Encryption StandardOld 56 bit cipher, broken by brute force and replaced by AES.On this site: Security fundamentals, WAN, MPLS and VPN
- DF
- Designated ForwarderThe one leaf elected per Ethernet segment to forward BUM traffic (EVPN type 4).On this site: Troubleshooting
- DF
- Don’t FragmentIPv4 header bit; set it in pings to test the real path MTU.On this site: Networking fundamentals, Troubleshooting
- DFS
- Distributed File SystemWindows feature that presents shares from many servers under one namespace and replicates them.On this site: Servers and virtualisation
- DFS
- Dynamic Frequency Selection5 GHz Wi-Fi rule that makes access points leave a channel when they detect radar.On this site: Troubleshooting, Wireless and mobile
- DFW
- Distributed FirewallStateful firewall at every VM vNIC; categories Ethernet to Application then default.On this site: Private cloud and storage, Troubleshooting
- DGX / HGX
- NVIDIA Integrated AI Systems / NVIDIA GPU Baseboard PlatformDGX is NVIDIA's own system; HGX boards sit inside Dell and other OEM servers.
- DH
- Diffie-HellmanKey agreement method; IKE proposals must use the same DH group at both ends.
- DHCP
- Dynamic Host Configuration ProtocolAutomatic addressing; relayed across subnets with ip helper address.On this site: Network automation, SD-Access campus fabric, VXLAN EVPN and ACI
- DHCPv6
- DHCP for IPv6Address assignment and options for IPv6.On this site: IP addressing and subnetting, Networking fundamentals, Troubleshooting
- DIA
- Dedicated Internet AccessUncontended business internet circuit.On this site: WAN, MPLS and VPN
- DIMM / DPC
- Dual Inline Memory Module / DIMMs Per ChannelMemory modules; two per channel can lower memory speed.
- DLC
- Direct Liquid CoolingCold plates on chips; required for current GPU racks.
- DLR
- Distributed Logical RouterNSX-V's in kernel router.
- DMTF
- Distributed Management Task ForceOwns the Redfish server management API standard.On this site: Troubleshooting
- DMVPN
- Dynamic Multipoint VPNCisco hub and spoke VPN with on demand spoke to spoke tunnels.On this site: Networking fundamentals, Routing protocols, SD-WAN and SDN
- DMZ
- Demilitarised ZoneZone between trusted and untrusted networks for exposed services.On this site: Cloud architecture, Data centre networks, Design authority
- DNAC
- DNA Centre (Digital Network Architecture Centre), Now Catalyst CenterCisco campus controller for SD-Access.
- DNAT
- Destination NATRewrites the destination to publish an inside server.On this site: VMware NSX
- DNP3
- Distributed Network Protocol 3SCADA protocol used by water and power utilities between control centres and outstations.On this site: Operational technology
- DNS
- Domain Name SystemName to address lookups on UDP and TCP 53; often the hidden cause of an outage.On this site: Network automation, SD-Access campus fabric, AWS, Azure and Google Cloud
- DNS64
- DNS Extensions for IPv6 to IPv4 TranslationMakes up AAAA records for IPv4 only names, so IPv6 only clients can reach them through NAT64.On this site: IP addressing and subnetting
- DNSSEC
- DNS Security ExtensionsSigns DNS records so answers can be verified.
- DOM
- Digital Optical MonitoringOptic readings of light levels, temperature and voltage.On this site: Networking fundamentals, Troubleshooting
- DORA
- Digital Operational Resilience ActEU Regulation 2022/2554, applying since 17 January 2025; shapes pod resilience evidence.On this site: Design authority, Resilience, risk and cost
- DORA
- Discover, Offer, Request, AcknowledgeThe four DHCP messages; a capture shows which step fails.On this site: Servers and virtualisation
- DoS
- Denial of ServiceAn attack that floods or exhausts a service so real users cannot reach it.On this site: Firewall platforms
- DP
- Data PlaneThe part of a device that forwards packets, as opposed to the control plane that decides where they go.On this site: Troubleshooting
- DP
- Data ProtectionBackup, replication and cyber recovery.
- DPD
- Dead Peer DetectionIKE keepalive that clears tunnels to a peer that has gone.On this site: Troubleshooting, WAN, MPLS and VPN
- DPDK
- Data Plane Development KitFast packet processing library used by the NSX Edge data plane.On this site: Troubleshooting, VMware NSX
- DPI
- Deep Packet InspectionLooking inside the payload, not just headers.On this site: Troubleshooting
- DPM
- Distributed Power ManagementvSphere feature that powers hosts down when a cluster is quiet and back up when load returns.On this site: Servers and virtualisation
- DPS
- Device Provisioning ServiceAzure IoT service that registers each device with the right IoT hub on first boot.On this site: IoT and edge
- DPU
- Data Processing UnitNetwork card with its own processors that takes networking, storage and security work off the host CPU.On this site: AI infrastructure
- DPU / SmartNIC
- Data Processing Unit / Smart Network Interface CardNIC with its own processors that offloads networking, storage and security.
- DR
- Designated RouterOSPF router that manages flooding on a broadcast segment. Also NSX Distributed Router.On this site: Routing protocols, Troubleshooting
- DR
- Disaster RecoveryRestoring service at another site after a major failure.On this site: Private cloud and storage
- DR
- Distributed RouterPart of each NSX gateway in every host's kernel. Also OSPF Designated Router.On this site: VMware NSX
- DR / DR4
- 500 m Singlemode Reach (4 lanes)400GBASE-DR4 uses 8 fibres of an MPO-12, 500 m.
- DRS
- Distributed Resource SchedulervSphere feature that balances VMs across hosts with vMotion.On this site: Private cloud and storage, Servers and virtualisation
- DS
- Distribution SystemThe wired network that joins access points together, in 802.11 terms.On this site: Wireless and mobile
- DSCP
- Differentiated Services Code Point6 bit QoS marking in the IP header; EF 46 for voice.On this site: AI infrastructure, Routing protocols, SD-WAN and SDN
- DSS
- Data Security StandardAs in PCI DSS, the card data security standard (v4.0.1 current).On this site: Data centre facilities, Data centre networks, Design authority
- DTLS
- Datagram Transport Layer SecurityTLS for UDP, used by CAPWAP, some VPNs and CoAP.On this site: SD-WAN and SDN, WAN, MPLS and VPN, Wireless and mobile
- DTP
- Dynamic Trunking ProtocolCisco trunk negotiation; turn it off with switchport nonegotiate.On this site: Security fundamentals, Switching and campus LAN, Troubleshooting
- DUAL
- Diffusing Update AlgorithmEIGRP's loop free path calculation with feasible successors.On this site: Troubleshooting
- DV
- Developed VettingThe highest level of UK national security vetting, for frequent access to TOP SECRET material.On this site: Government and defence
- DWDM
- Dense Wavelength Division MultiplexingMany wavelengths on one fibre pair.On this site: VXLAN EVPN and ACI, Data centre networks, WAN, MPLS and VPN
- DX
- Direct ExpansionRefrigerant based cooling inside a CRAC unit.
E
- EAP
- Extensible Authentication ProtocolAuthentication framework inside 802.1X and IKEv2, such as EAP-TLS.On this site: SD-Access campus fabric, Security fundamentals, WAN, MPLS and VPN
- EAPoL
- EAP over LANHow EAP is carried between the device and the switch in 802.1X.
- EAPOL
- EAP over LANCarries 802.1X authentication between a device and the switch or access point before the port opens.On this site: IoT and edge, Wireless and mobile
- eBGP
- External BGPBGP between different autonomous systems; AD 20.On this site: VXLAN EVPN and ACI, Data centre networks, Design authority
- eBGP / iBGP
- External BGP / Internal BGPBetween ASNs / within one ASN; eBGP underlay and iBGP EVPN is a common fabric pattern.
- EBS
- Elastic Block StoreAWS block storage volumes attached to EC2 instances.On this site: AWS, Azure and Google Cloud
- ECAB
- Emergency CABSmall group that authorises urgent changes quickly; the change is still reviewed afterwards.On this site: Support and service management, Troubleshooting
- ECC
- Error Correcting CodeMemory that detects and fixes bit errors.On this site: AI infrastructure
- ECDHE
- Elliptic Curve Diffie-Hellman with Temporary KeysKey exchange that makes fresh keys for each session, which gives TLS forward secrecy.On this site: Security fundamentals
- ECDSA
- Elliptic Curve Digital Signature AlgorithmSignature algorithm on elliptic curves, with smaller keys than RSA for the same strength.On this site: Security fundamentals
- ECH
- Encrypted Client HelloEncrypts the TLS Client Hello, including the server name, so the network cannot read it.On this site: Security
- ECIES
- Elliptic Curve Integrated Encryption SchemePublic key encryption built on elliptic curve key agreement.On this site: Security fundamentals
- ECMP
- Equal Cost Multi PathSeveral equal routes used at once, hashed per flow.On this site: AI infrastructure, VXLAN EVPN and ACI, Data centre networks
- ECN
- Explicit Congestion NotificationMarks packets instead of dropping them; with DCQCN it slows RoCE senders.On this site: AI infrastructure, Data centre networks, Networking fundamentals
- ECS
- Elastic Cloud StorageDell object storage, now ObjectScale.
- EDA
- Equipment Distribution AreaTIA-942 space where the server and storage racks sit.On this site: Data centre facilities
- EDA / HDA / MDA / ZDA / IDA
- Equipment / Horizontal / Main / Zone / Intermediate Distribution AreaTIA-942 cabling spaces from the main cross connect down to the racks.
- EdDSA
- Edwards Curve Digital Signature AlgorithmFast signature scheme on Edwards curves, such as Ed25519, common for SSH keys.On this site: Security fundamentals
- EDL
- External Dynamic ListPalo Alto list of addresses, URLs or domains pulled from a source and used in policy.
- EDR
- Endpoint Detection and ResponseAgent on servers and PCs that detects and contains attacks.On this site: Security fundamentals
- EEM
- Embedded Event ManagerCisco on box scripting triggered by events, useful for capturing evidence.On this site: WAN, MPLS and VPN
- EF
- Expedited ForwardingDSCP 46, the low latency class for voice.On this site: Routing protocols, Switching and campus LAN, Troubleshooting
- EFS
- Elastic File SystemAWS managed NFS storage shared across instances.On this site: AWS, Azure and Google Cloud
- EGP
- Exterior Gateway ProtocolThe first routing protocol between autonomous systems, replaced by BGP.On this site: Routing protocols
- EIA
- Electronic Industries AllianceOrigin of the EIA-310 standard for 19 inch racks.On this site: Data centre facilities
- EIA-310
- EIA-310 rack StandardDefines 19 inch racks and the 44.45 mm rack unit.On this site: Data centre facilities
- EID
- Endpoint IdentifierIn LISP and SD-Access, the endpoint's own address, mapped to the RLOC of the switch it sits behind.On this site: SD-Access campus fabric, Troubleshooting
- EIGRP
- Enhanced Interior Gateway Routing ProtocolCisco advanced distance vector protocol; AD 90 internal, 170 external.On this site: Networking fundamentals, Routing protocols, SD-WAN and SDN
- EIRP
- Effective Isotropic Radiated PowerTransmit power plus antenna gain minus cable loss; the figure regulators cap.On this site: Wireless and mobile
- EKS
- Elastic Kubernetes ServiceAWS managed Kubernetes.On this site: AWS, Azure and Google Cloud
- EMEA
- Europe, Middle East and AfricaThe sales and support region that covers those areas.On this site: Firewall platforms, Security fundamentals, Troubleshooting
- EMLSR
- Enhanced Multi Link Single RadioWi-Fi 7 mode where a single radio client listens on two links and switches to whichever is free.On this site: Wireless and mobile
- EoL
- End of LifeGeneral term for a product leaving sale and support.
- EoL / EoS
- End of Life / End of SupportVendor dates that drive evergreen refresh planning for each pod.
- EoS
- End of SaleLast date to order a product.
- EOS
- Extensible Operating SystemArista's network operating system.On this site: Data centre networks
- EoSWM
- End of Software MaintenanceNo more bug fix releases after this date.
- EoVSS
- End of Vulnerability and Security SupportNo more security fixes after this date.
- ePBR
- Enhanced Policy Based RedirectNX-OS service insertion that steers traffic through firewalls and load balancers.
- EPC
- Embedded Packet CaptureIOS XE on box capture with monitor capture.On this site: Troubleshooting, Wireless and mobile
- EPG
- Endpoint GroupACI group of workloads that share policy; contracts control traffic between them.On this site: Troubleshooting
- EPL
- Ethernet Private LineMEF point to point service with a dedicated port.On this site: WAN, MPLS and VPN
- EPMS
- Electrical Power Monitoring SystemDetailed metering and alarms across the power chain.On this site: Data centre facilities
- EPO
- Emergency Power OffSwitch that cuts power to a room in an emergency; guard against accidental use.
- ER
- Entrance RoomTIA-942 space where carrier circuits enter the building and meet the data centre cabling.On this site: Data centre facilities
- ER
- Extended ReachOptic class for longer singlemode links.On this site: VXLAN EVPN and ACI
- ERP
- Enterprise Resource PlanningBusiness system for finance, stock, orders and HR, such as SAP.On this site: Data centre facilities, IoT and edge, Operational technology
- ERSPAN
- Encapsulated Remote SPANMirrors traffic over IP in GRE to a remote analyser.On this site: Switching and campus LAN, Troubleshooting
- ES
- Ethernet SegmentThe set of links attaching one device to several leaves in EVPN multihoming.
- ESA / OSA
- Express Storage Architecture / Original Storage ArchitecturevSAN designs; ESA is NVMe only.
- ESG
- Edge Services GatewayNSX-V's edge router and services VM; replaced by Tier-0 and Tier-1.
- ESG
- Endpoint Security GroupACI security group that can span bridge domains within a VRF.
- ESI
- Ethernet Segment Identifier10 byte ID for EVPN multihoming; a standards based alternative to vPC.On this site: VXLAN EVPN and ACI, Data centre networks, Troubleshooting
- ESP
- Encapsulating Security PayloadIPsec encryption and integrity (IP protocol 50).On this site: Firewall platforms, Networking fundamentals, Security fundamentals
- EST
- Enrollment over Secure TransportLets devices request and renew certificates over HTTPS; the successor to SCEP.On this site: SD-Access campus fabric, IoT and edge, Troubleshooting
- EST / SCEP
- Enrollment over Secure Transport / Simple Certificate Enrollment ProtocolProtocols for devices to request certificates automatically.
- ESXi
- ESX Integrated (ESX was Elastic Sky X)VMware's bare metal hypervisor; NSX host transport nodes.On this site: Servers and virtualisation, SD-Access campus fabric, IP addressing and subnetting
- EtherChannel
- Cisco Name for a Port ChannelBundled links acting as one logical interface.On this site: Data centre networks, Support and service management, Switching and campus LAN
- EtherType
- Ethernet Frame Type FieldIdentifies the payload, for example 0x0800 IPv4 or 0x8100 802.1Q.On this site: Networking fundamentals, VMware NSX
- ETS
- Enhanced Transmission SelectionDCB bandwidth sharing between traffic classes (802.1Qaz).On this site: Private cloud and storage
- ETSI
- European Telecommunications Standards InstituteEuropean standards body for telecoms, including 5G, NFV and the EN 303 645 IoT security baseline.On this site: IoT and edge
- EU
- European UnionUnion of 27 European countries; the source of DORA, NIS2 and GDPR.On this site: Resilience, risk and cost
- EUI-64
- Extended Unique Identifier, 64 bitBuilds an IPv6 interface ID from a 48 bit MAC address by inserting FFFE in the middle and flipping one bit.On this site: IP addressing and subnetting
- EVC
- Enhanced vMotion CompatibilityvSphere CPU masking so VMs can move between CPU generations.On this site: Private cloud and storage, Servers and virtualisation
- EVI
- EVPN InstanceAn EVPN service, usually one per VLAN or VNI.
- EVPL
- Ethernet Virtual Private LineMEF point to point service sharing a port, split by VLAN.On this site: WAN, MPLS and VPN
- EVPL / EPL
- Ethernet Virtual Private Line / Ethernet Private LineCarrier Ethernet services sometimes used for DCI.
- EVPN
- Ethernet VPNBGP control plane for VXLAN; advertises MACs and IPs.On this site: Design authority, IP addressing and subnetting, SD-WAN and SDN
F to L
Terms from F to L
F
- FAST
- Flexible Authentication via Secure TunnellingCisco EAP method that builds a TLS tunnel from a protected access credential.On this site: Security
- FAT
- Factory Acceptance TestTests run at the factory before kit ships.On this site: Data centre facilities
- FC
- Fibre ChannelDedicated storage network protocol, run as fabric A and fabric B.On this site: Private cloud and storage
- FC / FCP
- Fibre Channel / Fibre Channel ProtocolLossless dedicated SAN transport; 32G and 64G today.
- FCA
- Financial Conduct AuthorityUK conduct regulator; operational resilience rules in PS21/3.On this site: Design authority, Resilience, risk and cost
- FCoE
- Fibre Channel over EthernetFC frames in Ethernet; uses the storage VDC on Nexus 7000.On this site: Data centre networks
- FCS
- Frame Check Sequence4 byte checksum at the end of every Ethernet frame.On this site: Networking fundamentals, Switching and campus LAN, Troubleshooting
- FDM
- Firepower Device ManagerOn box manager for a single FTD firewall.On this site: Firewall platforms
- FE
- Front End (network)The GPU or compute server network for users, services and storage access.
- FEC
- Forward Error CorrectionCorrects bit errors on high speed links; both ends must match.On this site: VXLAN EVPN and ACI, Troubleshooting
- FEX
- Fabric ExtenderNexus 2000 remote line card with no local switching.On this site: Data centre networks, Troubleshooting
- FGCP
- FortiGate Clustering ProtocolFortiGate HA heartbeat and sync; enable session pickup for state sync.On this site: Firewall platforms
- FHRP
- First Hop Redundancy ProtocolFamily name for HSRP, VRRP and GLBP.On this site: Troubleshooting
- FIB
- Forwarding Information BaseThe table the data plane actually forwards from.On this site: Routing protocols
- FIB / RIB
- Forwarding Information Base / Routing Information BaseThe hardware forwarding table / the routing table it is built from.
- FIDO2
- Fast IDentity Online 2Phishing resistant authentication with hardware keys.On this site: Security fundamentals
- FIP
- FCoE Initialization ProtocolDiscovers and logs in FCoE devices (EtherType 0x8914).
- FIPS
- Federal Information Processing StandardsFIPS 140 3 certifies HSMs.On this site: Security
- FLOGI
- Fabric LoginHow a Fibre Channel port logs in to the switch.On this site: Private cloud and storage
- FMC
- Firewall Management CenterCentral manager for Cisco FTD.On this site: Firewall platforms, Security
- FQDN
- Fully Qualified Domain NameComplete host name including the domain, as used in certificates.On this site: VMware NSX
- FR / FR4
- 2 km Singlemode Reach (4 wavelengths)400GBASE-FR4 runs 2 km over a duplex LC pair.
- FRR
- FRRoutingOpen source routing suite used by SONiC and Linux hosts (also Fast Reroute).
- FRU
- Field Replaceable UnitPart that can be swapped on site: PSU, fan, line card, optic.On this site: Support and service management
- FS
- Feasible SuccessorEIGRP's pre checked backup path.
- FSMO
- Flexible Single Master OperationActive Directory roles that only one domain controller holds at a time, such as the PDC emulator.On this site: Servers and virtualisation
- FT
- Fast Transition802.11r roaming that agrees keys with the next access point in advance, so voice calls do not drop.On this site: Wireless and mobile
- FTD
- Firepower Threat DefenseCisco NGFW: ASA data plane plus Snort.On this site: Troubleshooting
- FTP
- File Transfer ProtocolOld file transfer protocol with separate control and data channels.On this site: Firewall platforms, Networking fundamentals, Troubleshooting
- FTT
- Failures To ToleratevSAN policy: how many host or disk failures data survives.On this site: Private cloud and storage
- FTTP
- Fibre to the PremisesFibre all the way to the building, with no copper on the last stretch.On this site: WAN, MPLS and VPN
- FW
- FirewallPolicy enforcement point between zones.
- FWS
- Facility Water SystemThe building chilled water loop that feeds coolant distribution units for liquid cooled racks.On this site: Data centre facilities
- FWS / TCS
- Facility Water System / Technology Cooling SystemBuilding water loop / rack coolant loop, separated by the CDU.
- FXOS
- Firepower eXtensible Operating SystemChassis operating system on Firepower hardware.
G
- G0 / G1 / G2 / G3 / G4
- Pod Lifecycle Gates 0 to 4Gates a pod passes, from pod type agreed (G0) through signed designs and tests to handover (see Diagram P).
- GA
- General AvailabilityWhen a product release is fully supported, for example VCF 9.0 GA in June 2025.
- GARP
- Gratuitous ARPA device announcing its own address, used after gateway or firewall failover.On this site: Troubleshooting
- Gb/s vs GB/s
- Gigabits per Second Vs Gigabytes per SecondNetworks are quoted in bits, GPU and memory bandwidth often in bytes; 8 bits per byte.
- GCM
- Galois/Counter ModeAuthenticated encryption mode for AES, used in modern IPsec and TLS.On this site: Security fundamentals, WAN, MPLS and VPN
- GDPR
- General Data Protection RegulationData protection law (UK GDPR and EU GDPR); affects data placement and logging.On this site: Security fundamentals
- GDS
- GPUDirect StorageMoves data from storage straight into GPU memory.
- Gen4 / Gen5 / Gen6
- PCIe Generations16, 32 and 64 GT/s per lane; Gen5 x16 is about 63 GB/s each way.
- Geneve
- Generic Network Virtualisation EncapsulationNSX overlay on UDP 6081 (RFC 8926); needs 1600 MTU minimum.On this site: VXLAN EVPN and ACI, Networking fundamentals, Private cloud and storage
- GETVPN
- Group Encrypted Transport VPNCisco VPN with no tunnels that encrypts traffic across a private MPLS WAN, using keys shared by a group.On this site: WAN, MPLS and VPN
- GIPo
- Group IP OuterACI underlay multicast address used to flood traffic for a bridge domain.
- GIR
- Graceful Insertion and RemovalNX-OS maintenance mode that drains traffic before work.On this site: Data centre networks
- GKE
- Google Kubernetes EngineGoogle Cloud managed Kubernetes.On this site: AWS, Azure and Google Cloud
- GLBP
- Gateway Load Balancing ProtocolCisco first hop protocol that shares load across gateways.On this site: Switching and campus LAN
- GM
- Global ManagerNSX Federation manager for policy across sites.
- gNMI / gRPC
- gRPC Network Management Interface / gRPC Remote Procedure CallsStreaming telemetry and configuration over gRPC.
- GNSS
- Global Navigation Satellite SystemGPS and similar; the usual source for PTP grandmasters, with holdover if lost.On this site: Networking fundamentals, Troubleshooting
- GOOSE
- Generic Object Oriented Substation EventIEC 61850 multicast message for fast trip signals between protection relays.On this site: Operational technology
- GPFS
- General Parallel File SystemIBM Storage Scale; parallel file system used in HPC and AI.
- GPO
- Group Policy OptionVXLAN header extension carrying a group tag for policy; Nexus Dashboard 4.1 supports it.On this site: Security
- GPS
- Global Positioning SystemTime source for PTP grandmasters and stratum 1 NTP servers.
- GPU
- Graphics Processing UnitParallel processor for AI; drives power, cooling and back end network design.On this site: Data centre networks, Design authority, Private cloud and storage
- GPUDirect RDMA
- NVIDIA Feature NameLets the NIC read and write GPU memory directly.
- GRE
- Generic Routing EncapsulationPlain tunnel (IP protocol 47), 24 bytes overhead, no encryption.On this site: VXLAN EVPN and ACI, Networking fundamentals, SD-WAN and SDN
- GSC
- Government Security ClassificationsUK scheme since 2014: OFFICIAL, SECRET and TOP SECRET.
- GSLB
- Global Server Load BalancingDNS based load balancing and failover across sites.On this site: Load balancing, Troubleshooting
- GTM
- Global Traffic ManagerF5 GSLB product (now BIG-IP DNS).On this site: Load balancing
- GTSM
- Generalized TTL Security MechanismDrops BGP packets that arrive with a TTL below 255, so only a directly connected peer can reach the session.On this site: Security fundamentals
- GUI
- Graphical User InterfaceScreens and menus, as opposed to the command line or an API.On this site: Troubleshooting
- GWLB
- Gateway Load BalancerAWS service that sends traffic through a fleet of third party firewalls using GENEVE.On this site: Load balancing
H
- H1 / H2
- First Half / Second Half of the YearThe Prepare phase runs in H2 2026, ahead of UK delivery in 2027.
- HA
- High AvailabilityFirewall pairs or clusters with config and session sync.On this site: Load balancing, AWS, Azure and Google Cloud, Data centre networks
- HA1 / HA2
- Palo Alto HA Control Link / HA Data LinkHA1 carries heartbeats and config sync; HA2 syncs sessions.
- HBA
- Host Bus AdapterServer adapter for Fibre Channel.On this site: Private cloud and storage, Servers and virtualisation
- HBM
- High Bandwidth MemoryStacked memory on GPUs that feeds AI workloads.
- HCA
- Host Channel AdapterInfiniBand network adapter.
- HCI
- Hyperconverged InfrastructureCompute and storage in the same servers, such as vSAN or Nutanix.On this site: Servers and virtualisation
- HCL
- HashiCorp Configuration LanguageThe language Terraform files are written in.On this site: Network automation
- HCX
- VMware HCX (Hybrid Cloud Extension)Bulk VM migration between vSphere environments.On this site: Private cloud and storage
- HDA
- Horizontal Distribution AreaTIA-942 space where the horizontal cabling to the equipment rows starts.On this site: Data centre facilities
- HDFS
- Hadoop Distributed File SystemBig data storage layer, often on bare metal pods.On this site: AI infrastructure
- HDR / NDR / XDR
- InfiniBand Speed Generations200, 400 and 800 Gb/s per port.
- HLD
- High Level DesignArchitecture view of scope, topology and principles.On this site: Load balancing, SD-Access campus fabric, Design authority
- HMAC
- Hash Based Message Authentication CodeA hash keyed with a shared secret that proves a message was not changed.On this site: Security fundamentals, Security
- HMI
- Human Machine InterfaceThe operator screen that shows and controls an industrial process.On this site: IoT and edge, Operational technology
- HP
- Hewlett PackardNow split into HPE, which sells servers, storage and Aruba networking, and HP Inc for PCs and printers.On this site: Troubleshooting
- HPC
- High Performance ComputingLarge parallel compute jobs; shares design patterns with AI.On this site: AI infrastructure
- HPE
- Hewlett Packard EnterpriseCompleted its purchase of Juniper Networks on 2 July 2025.On this site: Resilience, risk and cost, Servers and virtualisation
- HRW
- Highest Random WeightA designated forwarder election method that spreads load across leaves.
- HSM
- Hardware Security ModuleTamper resistant device that stores keys and does cryptography without exposing them.On this site: IoT and edge, Resilience, risk and cost, Security fundamentals
- HSRP
- Hot Standby Router ProtocolCisco virtual gateway with active and standby routers.On this site: VXLAN EVPN and ACI, Data centre networks, Firewall platforms
- HTTP
- Hypertext Transfer ProtocolThe web's request and response protocol, on TCP 80.On this site: Load balancing, Networking fundamentals
- HTTP / HTTPS
- Hypertext Transfer Protocol (Secure)Web protocol used by REST APIs; HTTPS adds TLS.
- HTTPS
- HTTP SecureHTTP over TLS on TCP 443; device GUIs and APIs such as NSX Manager.On this site: Networking fundamentals, Load balancing, AWS, Azure and Google Cloud
- HV / LV
- High Voltage / Low VoltageIncoming supply and switchgear stages of the power chain.
- HVAC
- Heating, Ventilation and Air ConditioningThe building's mechanical cooling and air systems.On this site: IoT and edge, Operational technology
- HVO
- Hydrotreated Vegetable OilRenewable diesel alternative for standby generators.On this site: Data centre facilities
- HX
- Heat ExchangerTransfers heat between loops, for example a rear door HX or the CDU.
I
- I/O
- Input/OutputReads and writes between hosts and storage.On this site: Servers and virtualisation
- IA
- Inter AreaOSPF route learned from another area through an area border router, shown as O IA.On this site: Routing protocols
- IaaS
- Infrastructure as a ServiceCloud servers, storage and networks rented by the hour; you run everything above the hypervisor.On this site: Cloud architecture
- IaaS / PaaS / SaaS
- Infrastructure / Platform / Software as a ServiceCloud service layers.
- IaC
- Infrastructure as CodeInfrastructure defined in version controlled files and built by pipelines.
- IAM
- Identity and Access ManagementManaging user identities and what they can reach.On this site: AWS, Azure and Google Cloud
- IANA
- Internet Assigned Numbers AuthorityAssigns port numbers, protocol numbers and top level address blocks.On this site: Network automation
- IAW
- In Accordance WithShorthand in specifications and contracts: the work must follow the named document.
- IB
- InfiniBandLossless, low latency fabric for AI training; mainly NVIDIA.
- iBGP
- Internal BGPBGP inside one AS; AD 200; needs a full mesh or route reflectors.On this site: VXLAN EVPN and ACI, Data centre networks, Routing protocols
- IBNS
- Identity Based Networking ServicesCisco framework for 802.1X, MAB and policy on switch ports.On this site: SD-Access campus fabric
- IBS
- Important Business ServiceA service whose disruption would harm customers or markets; impact tolerances apply to it.On this site: Design authority
- ICMP
- Internet Control Message ProtocolPing, traceroute and error messages; never block all of it at a boundary.On this site: Load balancing, VXLAN EVPN and ACI, Firewall platforms
- ICMP / ICMPv6
- Internet Control Message Protocol (for IPv6)Ping, traceroute and path MTU discovery depend on it; ICMPv6 also carries NDP.
- ICMPv6
- Internet Control Message Protocol for IPv6Carries IPv6 errors, ping, neighbour discovery and packet too big messages.On this site: IP addressing and subnetting, Networking fundamentals
- ICO
- Information Commissioner's OfficeThe UK data protection regulator; serious personal data breaches go to it within 72 hours.On this site: Security fundamentals
- ICT
- Information and Communication TechnologyDORA's term for technology risk, incidents and third parties.On this site: Design authority, Resilience, risk and cost
- ICV
- Integrity Check ValueMACsec trailer that proves the frame was not altered.On this site: Security fundamentals, WAN, MPLS and VPN
- ID
- IdentifierFor example VLAN ID, VNI or router ID.On this site: SD-Access campus fabric, VXLAN EVPN and ACI, Data centre networks
- IDA
- Intermediate Distribution AreaTIA-942 space between the main and horizontal distribution areas in a large data hall.On this site: Data centre facilities
- IDevID
- Initial Device IdentifierCertificate a maker installs in a device at the factory, under IEEE 802.1AR.On this site: IoT and edge, Troubleshooting, Security
- IdP
- Identity ProviderCentral login service for single sign on.
- iDRAC
- Integrated Dell Remote Access ControllerDell's BMC; managed through Redfish.On this site: Servers and virtualisation
- IDS
- Intrusion Detection SystemDetects and alerts on attacks without blocking.On this site: SD-Access campus fabric, SD-WAN and SDN, Security fundamentals
- IDS / IPS
- Intrusion Detection System / Intrusion Prevention SystemDetects or blocks attacks in traffic; built into NGFWs.
- IE
- Industrial EthernetHardened switches and protocols for factories and plants.On this site: SD-Access campus fabric
- IEC
- International Electrotechnical CommissionCo publisher of ISO/IEC standards such as 20000 and 27001.On this site: IoT and edge
- IEEE
- Institute of Electrical and Electronics EngineersPublishes Ethernet (802.3), VLAN (802.1Q) and 802.1X standards.On this site: IoT and edge, Security fundamentals, Wireless and mobile
- IETF
- Internet Engineering Task ForcePublishes RFCs: BGP, OSPF, VXLAN, Geneve and more.On this site: Network automation, Security
- IFRS
- International Financial Reporting StandardsIFRS 16 decides whether a dedicated hall or as a service deal is treated as a lease.
- IG-541 / IG-55
- Inert Gas Fire Suppression AgentsGaseous suppression for data halls.
- IGMP
- Internet Group Management ProtocolHow hosts join multicast groups; switches snoop it.On this site: VXLAN EVPN and ACI, Networking fundamentals, Operational technology
- IGP
- Interior Gateway ProtocolRouting inside one network: OSPF, EIGRP, IS-IS.On this site: VXLAN EVPN and ACI, Routing protocols, Troubleshooting
- IKE
- Internet Key ExchangeSets up IPsec keys on UDP 500 (4500 with NAT); v1 and v2.On this site: Networking fundamentals, Security fundamentals, Troubleshooting
- IKEv1
- Internet Key Exchange Version 1The first IPsec key exchange; older and chattier, with main and aggressive modes.On this site: Troubleshooting, WAN, MPLS and VPN
- IKEv2
- Internet Key Exchange Version 2The current IPsec key exchange, with fewer messages and built in NAT traversal and dead peer detection.On this site: Security, Troubleshooting, WAN, MPLS and VPN
- iLO
- Integrated Lights OutHPE's BMC.On this site: Servers and virtualisation, Home lab
- IMAP
- Internet Message Access ProtocolLets a mail client read mail that stays on the server, on TCP 143, or 993 with TLS.On this site: Networking fundamentals
- IMET
- Inclusive Multicast Ethernet TagEVPN route type 3, which builds BUM flood lists.
- IO
- Input and OutputData moving to and from storage, the network or a device; storage IO is often counted in IOPS.On this site: Operational technology, Troubleshooting
- IOPS
- Input/Output Operations Per SecondStorage performance measure alongside latency and throughput.On this site: Design authority, Servers and virtualisation
- IOS
- Internetwork Operating SystemCisco software on Catalyst and ISR; IOS XE is the newer version on 3850, Catalyst 9000 and ISR 4000.On this site: Network automation, SD-Access campus fabric, IP addressing and subnetting
- IOS XE
- Cisco Internetwork Operating System XECisco campus and router operating system.On this site: Network automation, SD-Access campus fabric, Routing protocols
- IoT
- Internet of ThingsSensors, cameras and controllers connected to a network.On this site: SD-Access campus fabric, IoT and edge, IP addressing and subnetting
- IoT / MQTT
- Internet of Things / Message Queuing Telemetry TransportSensor devices and their lightweight messaging protocol.
- IP
- Internet ProtocolLayer 3 addressing and routing; IPv4 is 32 bit, IPv6 is 128 bit.On this site: AWS, Azure and Google Cloud, Firewall platforms, IoT and edge
- IP SLA
- Internet Protocol Service Level AgreementCisco probes that measure a path and trigger tracked failover.On this site: Network automation, Routing protocols, Support and service management
- IPAM
- IP Address ManagementTool and records for address plans.On this site: Network automation, Data centre facilities, Data centre networks
- IPFIX
- IP Flow Information ExportIETF flow export standard (RFC 7011); NSX supports it.On this site: Network automation, SD-WAN and SDN, Support and service management
- IPFIX / NetFlow
- IP Flow Information Export / Cisco Flow ExportFlow records for traffic analysis and security.
- IPMI
- Intelligent Platform Management InterfaceOlder BMC protocol, replaced by Redfish.On this site: Servers and virtualisation
- IPN
- Inter Pod NetworkRouted network joining ACI Multi-Pod pods; needs PIM Bidir, DHCP relay and larger MTU; 50 ms RTT limit.On this site: VXLAN EVPN and ACI, Troubleshooting
- IPS
- Intrusion Prevention SystemInline engine that blocks attacks; in NGFWs and NSX vDefend.On this site: SD-WAN and SDN, Security fundamentals, Troubleshooting
- IPsec
- Internet Protocol SecurityEncrypts and authenticates IP traffic between peers.On this site: Cloud architecture, VXLAN EVPN and ACI, Firewall platforms
- IPSG
- IP Source GuardSwitch feature that drops traffic from an IP and MAC pair the DHCP snooping table does not know.On this site: Security fundamentals, Troubleshooting
- IPv4
- Internet Protocol Version 432 bit addressing, written as four numbers.On this site: Troubleshooting, WAN, MPLS and VPN
- IPv4 / IPv6
- Internet Protocol Version 4 / Version 632 bit versus 128 bit addressing.
- IPv6
- Internet Protocol Version 6128 bit addressing; needs its own ACLs and ICMPv6 rules.On this site: SD-Access campus fabric, AWS, Azure and Google Cloud, IoT and edge
- iPXE
- Open Source Network Boot Firmware (PXE extended)Adds HTTP boot and scripting to PXE for automated builds.On this site: Private cloud and storage, Troubleshooting
- IQN
- iSCSI Qualified NameNames iSCSI initiators and targets.On this site: Private cloud and storage
- IRB
- Integrated Routing and BridgingLeaves both route and bridge in the overlay; symmetric IRB uses an L3 VNI (RFC 9135).On this site: VXLAN EVPN and ACI
- IRE
- Isolated Recovery EnvironmentThe cyber vault and clean room for recovery after ransomware.
- IS-IS
- Intermediate System to Intermediate SystemLink state protocol over layer 2; under FabricPath, OTV and ACI.On this site: SD-Access campus fabric, VXLAN EVPN and ACI, Data centre networks
- ISAKMP
- Internet Security Association and Key Management ProtocolThe framework IKEv1 phase 1 builds on; shows in ASA and IOS output.
- iSCSI
- Internet Small Computer Systems InterfaceBlock storage over TCP 3260.On this site: VXLAN EVPN and ACI, Private cloud and storage, Servers and virtualisation
- ISE
- Identity Services EngineCisco RADIUS and TACACS+ policy server.On this site: SD-Access campus fabric, IoT and edge, Private cloud and storage
- iSER
- iSCSI Extensions for RDMAiSCSI over RDMA transports.On this site: Private cloud and storage
- ISMS
- Information Security Management SystemThe managed set of security policies and controls that ISO 27001 certifies.On this site: Government and defence, Security fundamentals
- ISN
- Inter Site NetworkRouted network joining ACI Multi-Site fabrics; no multicast needed.On this site: VXLAN EVPN and ACI
- ISO
- International Organization for StandardizationPublishes ISO/IEC 20000 and 27001 with the IEC.On this site: Data centre facilities, Design authority, Government and defence
- ISO 20000
- ISO/IEC 20000 1, service Management System StandardInternational standard for IT service management.
- ISO 27001
- ISO/IEC 27001, information Security Management StandardCertifiable standard for an ISMS; drives audits, access control and change evidence.On this site: Government and defence, Security
- ISP
- Internet Service ProviderUpstream internet connectivity at the border.On this site: WAN, MPLS and VPN
- ISR
- Integrated Services RouterISR 4000 last date of support 30 Nov 2028.On this site: Support and service management, Switching and campus LAN, Troubleshooting
- ISSU
- In Service Software UpgradeUpgrade while forwarding, usually with dual supervisors.On this site: Data centre networks, Support and service management, Troubleshooting
- IST
- Integrated Systems TestFinal commissioning test of power, cooling and controls working together.On this site: Data centre facilities
- IST
- Internal Spanning TreeMST instance 0, which talks to switches outside the region.
- IT
- Information TechnologyOffice and business computing, as opposed to OT on the plant floor.On this site: IoT and edge, IP addressing and subnetting, Operational technology
- IT / OT
- Information Technology / Operational TechnologyBusiness IT versus building and industrial control systems; keep OT segmented.
- ITAD
- IT Asset DispositionSecure, certified retirement of old kit at the end of each pod's life.
- ITAM
- IT Asset ManagementTracks hardware and software through their life; feeds lifecycle and refresh planning.
- ITIC
- Information Technology Industry CouncilPublishes the ITIC curve of power quality IT kit should survive.On this site: Data centre facilities
- ITIL
- Information Technology Infrastructure LibraryITIL 4 and ITIL (Version 5) from 2026.On this site: Design authority, Government and defence, Resilience, risk and cost
- ITSM
- IT Service ManagementRunning IT as services with defined processes; what ITIL and SD+ support.
- ITU
- International Telecommunication UnionSets the DWDM wavelength grid and telecoms standards.On this site: WAN, MPLS and VPN
- IV
- Initialisation VectorA unique value that makes the same plaintext encrypt differently each time.On this site: WAN, MPLS and VPN
- iVXLAN
- ACI Internal VXLANACI's VXLAN variant that also carries the policy group of the source.
J
- JCT
- Job Completion TimeTraining job duration; set by the slowest flow, so network quality matters.
- JIT
- Just In Time (access)Privileges granted only for the task and time needed.
- JSON
- JavaScript Object NotationData format used by REST APIs such as NSX's.On this site: Network automation, AWS, Azure and Google Cloud, Troubleshooting
- JSON / YAML
- JavaScript Object Notation / YAML Ain't Markup LanguageData formats for APIs and automation files.
- JTAG
- Joint Test Action GroupHardware debug port on a circuit board; a way in for an attacker if left open on a device.On this site: Troubleshooting
K
- K8s
- KubernetesContainer orchestration platform (8 letters between K and s).
- KAVG
- Kernel Average LatencyESXi esxtop latency inside the hypervisor.On this site: Servers and virtualisation
- KDC
- Key Distribution CentreThe Kerberos service on each domain controller that issues tickets.On this site: Servers and virtualisation
- KEDB
- Known Error DatabaseStore of known errors and workarounds so 1st and 2nd line can fix repeats fast.
- KEV
- Known Exploited Vulnerabilities (catalogue)CISA list of flaws exploited in the wild; patch these first.On this site: Support and service management
- KMIP
- Key Management Interoperability ProtocolStandard interface between storage or apps and the key manager.On this site: Private cloud and storage, Troubleshooting
- KMS
- Key Management ServiceManages the lifecycle of encryption keys; a tier zero shared service.On this site: Resilience, risk and cost, Troubleshooting
- KPI
- Key Performance IndicatorMeasure of service performance, such as resolution within SLA.On this site: Troubleshooting
- kVA / kW
- Kilovolt Ampere / KilowattApparent versus real power; kW = kVA × PF.
- KVM
- Kernel Based Virtual MachineLinux hypervisor used by OpenShift Virtualisation and OpenStack.On this site: Servers and virtualisation
- kWh
- Kilowatt HourEnergy used: one kW for one hour; the unit behind power bills and PUE.On this site: AI infrastructure, Data centre facilities, Resilience, risk and cost
L
- L1 / L2 / L3 / L4 / L7
- Layer 1 / 2 / 3 / 4 / 7 of the OSI ModelPhysical, data link, network, transport and application layers.
- L2
- Layer 2Data link layer: MAC addresses, switching and VLANs.On this site: Troubleshooting
- L2VNI
- Layer 2 VNIVXLAN network identifier for one bridged segment, mapped to a VLAN.On this site: VXLAN EVPN and ACI, Troubleshooting
- L2VNI / L3VNI
- Layer 2 / Layer 3 VXLAN Network IdentifierL2VNI maps to a VLAN for bridging; L3VNI maps to a VRF for routing.
- L2VPN
- Layer 2 Virtual Private NetworkCarrier service carrying Ethernet frames, such as VPLS or EVPN.
- L3
- Layer 3Network layer: IP addressing and routing.On this site: Troubleshooting, Home lab
- L3Out
- Layer 3 OutsideACI object that peers a VRF with external routers through border leaves.On this site: VXLAN EVPN and ACI, Troubleshooting, VMware NSX
- L3VNI
- Layer 3 VNIVXLAN network identifier for a tenant VRF, used for routed traffic between leaves.On this site: VXLAN EVPN and ACI, Troubleshooting
- L3VPN
- Layer 3 VPNCarrier IP VPN using VRFs and MP-BGP (RFC 4364).On this site: VXLAN EVPN and ACI, WAN, MPLS and VPN
- L3VPN / L2VPN
- Layer 3 / Layer 2 Virtual Private NetworkMPLS or EVPN based VPN services, often at the WAN handoff.
- LACP
- Link Aggregation Control ProtocolNegotiates EtherChannel bundles; at least one end in active mode.On this site: Networking fundamentals, Servers and virtualisation, Switching and campus LAN
- LAG
- Link Aggregation GroupSeveral links acting as one; also called port channel, bond or EtherChannel.On this site: Switching and campus LAN, Troubleshooting
- LAN
- Local Area NetworkThe network inside a building or campus.On this site: Load balancing, SD-Access campus fabric, VXLAN EVPN and ACI
- LAN / WAN
- Local Area Network / Wide Area NetworkIn site versus between site networks.
- LB
- Load BalancerSpreads client connections across a pool of servers and takes failed ones out.On this site: Troubleshooting
- LB / ADC
- Load Balancer / Application Delivery ControllerSpreads traffic across servers with health checks.
- LC
- Lucent ConnectorSmall form factor duplex fibre connector.On this site: Data centre facilities
- LCP
- Local Control PlaneNSX agent on each transport node that receives state from the CCP.
- LCST
- Logistic Commodities and Services TransformationUK MOD programme under which an industry partner runs the storage and distribution of defence supplies.
- LDAP
- Lightweight Directory Access ProtocolHow ISE and AAA servers query directories such as Active Directory.On this site: Network automation, Data centre networks, Networking fundamentals
- LDAPS
- LDAP SecureLDAP over TLS, on TCP 636.On this site: Networking fundamentals
- LDevID
- Locally Significant Device IdentifierCertificate an organisation issues to a device after onboarding, alongside its factory IDevID.On this site: IoT and edge, Security
- LDoS
- Last Date of SupportAfter this date no TAC, fixes or replacements.On this site: Troubleshooting
- LDP
- Label Distribution ProtocolShares MPLS labels between routers on TCP and UDP 646.On this site: WAN, MPLS and VPN
- LID
- Local IdentifierInfiniBand address assigned by the subnet manager.
- LISP
- Locator/ID Separation ProtocolControl plane of Cisco SD-Access fabrics.On this site: SD-Access campus fabric, VXLAN EVPN and ACI, SD-WAN and SDN
- LLD
- Low Level DesignDetailed build: ports, addressing, VLANs and configs; used to check what was actually built.On this site: Load balancing, SD-Access campus fabric, Design authority
- LLDP
- Link Layer Discovery ProtocolIEEE 802.1AB neighbour discovery across vendors.On this site: Network automation, SD-Access campus fabric, VXLAN EVPN and ACI
- LLM
- Large Language ModelThe AI models driving GPU demand.
- LLQ
- Low Latency QueuingStrict priority queue for voice, policed so it cannot starve others.On this site: Routing protocols, Troubleshooting, WAN, MPLS and VPN
- LM
- Local ManagerNSX Manager cluster at one site under Federation.
- LoRaWAN
- Long Range Wide Area NetworkLow power radio network for sensors that send small readings over kilometres.On this site: IoT and edge
- LPDDR5X
- Low Power Double Data Rate 5XMemory used with NVIDIA Grace CPUs.
- LR
- Long ReachOptics that reach 10 km over single mode fibre.On this site: VXLAN EVPN and ACI
- LR / LR4
- Long Reach, 10 km on single mode fibre (LR4 uses 4 wavelengths)Common for campus and short DCI links.
- LSA
- Link State AdvertisementOSPF's unit of routing information; types 1 to 7.On this site: Routing protocols
- LSDB
- Link State DatabaseEach OSPF router's copy of the whole area map, from which it works out its routes.On this site: Troubleshooting
- LSP
- Label Switched PathThe path an MPLS packet follows through the core.
- LSR
- Label Switch RouterAn MPLS router that forwards on labels.On this site: Routing protocols
- LSR
- Link State RequestOSPF packet that asks a neighbour for link state advertisements it is missing.On this site: Routing protocols
- LSU
- Link State UpdateOSPF packet that carries link state advertisements.On this site: Routing protocols
- LSZH
- Low Smoke Zero HalogenCable sheath that limits toxic smoke in a fire.
- LTM
- Local Traffic ManagerThe F5 BIG-IP module that load balances application traffic.On this site: Load balancing
- LUN
- Logical Unit NumberA storage volume presented to a host.On this site: Private cloud and storage, Servers and virtualisation
- LWT
- Last Will and TestamentMQTT message the broker publishes for a client that drops off without warning.On this site: Troubleshooting
M to R
Terms from M to R
M
- M&E
- Mechanical and ElectricalBuilding services.
- MAB
- MAC Authentication Bypass802.1X fallback using the MAC as identity; weaker, so restrict it.On this site: SD-Access campus fabric, IoT and edge, Security fundamentals
- MAC
- Mandatory Access ControlType enforcement in Sidewinder's hardened OS. Also Media Access Control address.
- MAC
- Media Access Control48 bit layer 2 address that switches learn and forward on.On this site: Networking fundamentals, Switching and campus LAN, Network automation
- MACsec
- MAC Security (IEEE 802.1AE)Hop by hop encryption on Ethernet links.On this site: VXLAN EVPN and ACI, Government and defence, Security fundamentals
- MACsec / MKA
- Media Access Control Security / MACsec Key AgreementIEEE 802.1AE line rate layer 2 encryption; protects DCI links.
- MC-LAG
- Multi Chassis Link Aggregation GroupGeneric name for bundles across two switches, such as vPC.On this site: Switching and campus LAN
- MCITP
- Microsoft Certified IT ProfessionalTraining completed, not certified; say trained.On this site: Servers and virtualisation
- MCLAG / MLAG
- Multi Chassis Link Aggregation (Group)Two switches act as one for a port channel; Cisco's version is vPC.
- MCSE
- Microsoft Certified Systems EngineerTraining completed, not certified; say trained.On this site: Servers and virtualisation
- MD5
- Message Digest 5Old hash still used to check image files; prefer SHA 512 where offered.On this site: Routing protocols, Security fundamentals, Troubleshooting
- MDA
- Main Distribution AreaTIA-942 core cabling space, home to the core routers and switches.On this site: Data centre facilities
- MDC / SN
- Very Small Form Factor Fibre ConnectorsDenser than LC; appearing for 800G breakouts.
- MDS
- Cisco MDS 9000 (Fibre Channel switch family)Cisco's SAN switches.On this site: Private cloud and storage
- MEC
- Multichassis EtherChannelA bundle from one device to both chassis of a VSS pair.On this site: Support and service management
- MED
- Multi Exit DiscriminatorBGP attribute that suggests an entry point to a neighbour AS; lower wins.On this site: Routing protocols
- MEF
- MEF (formerly the Metro Ethernet Forum)Defines carrier Ethernet services: E-Line, E-LAN, E-Tree.On this site: WAN, MPLS and VPN
- MES
- Manufacturing Execution SystemsSoftware that runs production on the shop floor, between ERP and the control systems.On this site: AI infrastructure, Cloud architecture, IoT and edge
- MF
- More FragmentsIPv4 header flag that says more fragments of this packet follow.On this site: Networking fundamentals
- MFA
- Multi Factor AuthenticationTwo or more proofs of identity for admin and remote access.On this site: AWS, Azure and Google Cloud, Cloud architecture, Data centre networks
- mGRE
- Multipoint GREOne tunnel interface reaching many peers; the base of DMVPN.
- MHz
- MegahertzMillion cycles a second.On this site: IoT and edge, Wireless and mobile
- MIB
- Management Information BaseThe structure of values an SNMP agent exposes.
- MIC
- Message Integrity CodeCheck value that shows whether a message was tampered with, such as in the WPA handshake.On this site: Wireless and mobile
- MID
- Management, Instrumentation and Discovery (MID Server)ServiceNow agent that runs discovery inside the network.On this site: Network automation
- MiFID
- Markets in Financial Instruments DirectiveEU and UK financial markets regulation; version II applies.On this site: VXLAN EVPN and ACI, Data centre networks, Design authority
- MiFID II
- Markets in Financial Instruments Directive IIDrives trade timestamp accuracy (RTS 25)On this site: VXLAN EVPN and ACI, Data centre networks, Design authority
- MIG
- Multi Instance GPUSplits one NVIDIA GPU into up to seven isolated instances.On this site: AI infrastructure
- MIM
- Major Incident ManagementThe process for the highest priority incidents, with a named manager, a bridge call and regular updates.
- MKA
- MACsec Key AgreementFinds MACsec peers and agrees keys between them, under IEEE 802.1X.On this site: VXLAN EVPN and ACI, Security fundamentals
- MLD
- Multicast Listener DiscoveryIPv6 equivalent of IGMP.
- MLO
- Multi Link OperationWi-Fi 7 feature that lets a client use links on more than one band at once.On this site: Wireless and mobile
- MM
- MultimodeFibre type for short runs (OM3, OM4, OM5).On this site: Troubleshooting
- MMF / SMF
- Multimode Fibre / Singlemode FibreShort reach (OM grades) versus long reach (OS2).
- MMR
- Meet Me RoomWhere carriers and customers cross connect in a colocation building.
- MMS
- Manufacturing Message SpecificationIEC 61850 client and server protocol for reading and controlling substation devices.On this site: Operational technology
- MnT
- Monitoring and TroubleshootingThe Cisco ISE persona that collects logs and runs reports.On this site: SD-Access campus fabric, Security
- MOD
- Ministry of DefenceThe UK government department for defence.On this site: Government and defence
- MOM
- Manufacturing Operations ManagementThe layer between business systems and plant control that plans and tracks production.On this site: IoT and edge, Operational technology
- MOP
- Method of ProcedureStep by step change plan with checks and rollback.
- MP
- Management PlaneNSX Manager GUI, API and desired state.On this site: Troubleshooting
- MP-BGP
- Multiprotocol BGPBGP extensions that carry VPNv4, IPv6 and EVPN routes.On this site: VXLAN EVPN and ACI, Routing protocols, VMware NSX
- MPI
- Message Passing InterfaceStandard for communication between HPC processes.On this site: AI infrastructure
- MPIO
- Multipath I/OHost software that uses several paths to storage for resilience.
- MPLS
- Multiprotocol Label SwitchingLabel forwarding under carrier VPNs.On this site: VXLAN EVPN and ACI, Data centre networks, Firewall platforms
- MPO
- Multi Fibre Push onConnector with 12 or more fibres in one ferrule, used for 40G and faster links.On this site: Data centre facilities
- MPO / MTP
- Multi Fibre Push On / MTP Is a Branded MPO8 to 24 fibre connectors for parallel optics and trunks.
- MPO-12
- MPO, 12 fibresCommon trunk connector for 40G and 100G SR4.On this site: Data centre facilities
- MPO-16
- MPO, 16 fibresConnector for 400G SR8 and 800G optics.On this site: Data centre facilities
- MPO-24
- MPO, 24 fibresHigh count trunk connector.On this site: Data centre facilities
- MQC
- Modular QoS CLICisco QoS config model: class maps, policy maps, service policies.On this site: Switching and campus LAN
- MQTT
- Message Queuing Telemetry TransportLightweight publish and subscribe protocol for IoT, through a broker on TCP 1883 or 8883.On this site: IoT and edge, Networking fundamentals, Operational technology
- MRDIMM
- Multiplexed Rank DIMMHigher bandwidth server memory module.
- MSCHAPv2
- Microsoft Challenge Handshake Authentication Protocol Version 2Password challenge method used inside PEAP; weak on its own, so the TLS tunnel around it matters.On this site: Security
- MSD
- Multi-Site DomainNexus Dashboard fabric type that groups member fabrics joined by border gateways.
- MSDP
- Multicast Source Discovery ProtocolShares multicast source information between rendezvous points, for anycast RP or between domains.On this site: Routing protocols
- MSEE
- Microsoft Enterprise EdgeThe Microsoft routers an ExpressRoute circuit lands on.On this site: AWS, Azure and Google Cloud
- MSO
- Multi-Site OrchestratorFormer name of Nexus Dashboard Orchestrator.
- MSS
- Maximum Segment SizeTCP payload size; clamp it on tunnels to avoid MTU faults.On this site: VXLAN EVPN and ACI, Data centre networks, Firewall platforms
- MST
- Multiple Spanning TreeIEEE 802.1s; many VLANs mapped to a few instances.On this site: Data centre networks, Troubleshooting
- MSTP / MST
- Multiple Spanning Tree ProtocolIEEE 802.1s spanning tree with several instances.
- MT/s
- Megatransfers per SecondMemory transfer rate, for example DDR5 6400 MT/s.On this site: Servers and virtualisation
- MT/s / GT/s
- Megatransfers / Gigatransfers per SecondMemory and PCIe signalling rates.
- MTBF
- Mean Time Between FailuresAverage running time between failures; higher is better.On this site: Resilience, risk and cost
- MTEP / O MTEP
- Multicast TEP / Overlay Multicast TEPACI Multi-Site addresses used for head end replication toward remote sites.
- mTLS
- Mutual Transport Layer SecurityBoth client and server present certificates, so each proves who it is.
- MTTD
- Mean Time to DetectAverage time from a fault or attack starting to someone knowing about it.On this site: Resilience, risk and cost
- MTTR
- Mean Time To Repair (or Restore)Average time to restore service; good observability lowers it.On this site: Resilience, risk and cost
- MTU
- Maximum Transmission UnitLargest packet a link carries; NSX Geneve needs at least 1600 on the underlay.On this site: SD-Access campus fabric, AWS, Azure and Google Cloud, VXLAN EVPN and ACI
- MTV
- Migration Toolkit for VirtualisationRed Hat tool to move VMs from VMware to OpenShift Virtualisation.On this site: Troubleshooting
- MVPN
- Multicast VPNMulticast inside an MPLS VPN.On this site: VXLAN EVPN and ACI
- MW
- MegawattData hall and site capacity is quoted in MW of IT load.
- mW
- MilliwattThousandth of a watt; optical power levels.On this site: Wireless and mobile
- MX
- Mail ExchangeDNS record that names the mail servers for a domain.On this site: Networking fundamentals
N
- N-VDS
- NSX Virtual Distributed SwitchNSX's own host switch; removed on ESXi in NSX 4.0, still used on Edges.On this site: VMware NSX
- NA
- Neighbour AdvertisementIPv6 neighbour discovery reply that gives a node's MAC address, like an ARP reply.On this site: IP addressing and subnetting
- NAC
- Network Access ControlControls which devices may join the network, for example with ISE.On this site: Security, Troubleshooting, Wireless and mobile
- NACL
- Network ACLStateless AWS subnet filter, checked in both directions.On this site: AWS, Azure and Google Cloud
- NAD
- Network Access DeviceThe switch, access point or VPN gateway that asks ISE or RADIUS whether to let a device in.On this site: Troubleshooting
- NAPALM
- Network Automation and Programmability Abstraction Layer with Multivendor SupportPython library that gives one set of functions to read and push configuration on many vendors' devices.On this site: Network automation
- NAS
- Network Attached StorageFile storage over the network, using NFS (Network File System) or SMB (Server Message Block).On this site: Private cloud and storage, Servers and virtualisation
- NAT
- Network Address TranslationRewrites addresses at a boundary; check if rules use pre or post NAT addresses.On this site: Load balancing, AWS, Azure and Google Cloud, VXLAN EVPN and ACI
- NAT / PAT
- Network Address Translation / Port Address TranslationRewrites addresses (and ports) at a boundary; avoid inside the DC.
- NAT-T
- NAT TraversalPuts ESP inside UDP 4500 so IPsec works through NAT.On this site: Troubleshooting, WAN, MPLS and VPN
- NAT64
- NAT from IPv6 to IPv4Lets IPv6 only hosts reach IPv4 services.On this site: IP addressing and subnetting
- NBMA
- Non Broadcast Multiple AccessNetworks such as DMVPN with many peers but no broadcast; OSPF needs care on them.On this site: WAN, MPLS and VPN
- NCC
- Network Connectivity CenterGoogle Cloud hub for joining VPCs, sites and partner networks.On this site: Cloud architecture
- NCC
- Network Coordination CentreAs in RIPE NCC, the European regional internet registry.On this site: VXLAN EVPN and ACI, Data centre networks, IP addressing and subnetting
- NCCL
- NVIDIA Collective Communications LibraryRuns GPU collective operations (all reduce) over NVLink and the network.On this site: Private cloud and storage, Troubleshooting
- NCGI
- National Centre for Geospatial IntelligencePublic MOD organisation within Defence Intelligence.
- NCM
- Network Configuration ManagerSolarWinds config backup, change detection and compliance tool.
- NCSC
- National Cyber Security CentreUK technical authority; patch timings, cross domain and device security guidance.On this site: Data centre facilities, Government and defence, Security fundamentals
- ND
- Neighbour DiscoveryIPv6 protocol, carried in ICMPv6, that replaces ARP and finds routers and neighbours.On this site: Troubleshooting
- ND
- Nexus DashboardCisco's operations platform; 4.1 unifies Fabric Controller, Insights and Orchestrator.On this site: Troubleshooting
- ND / NDP
- Neighbor Discovery (Protocol)IPv6 replacement for ARP and router discovery.
- NDA
- Non Disclosure AgreementGoverns what vendor roadmap and pricing detail can be shared in evaluations.
- NDFC
- Nexus Dashboard Fabric ControllerCisco's current fabric management tool for NX-OS fabrics.On this site: VXLAN EVPN and ACI
- NDI
- Nexus Dashboard InsightsAnalytics, assurance and telemetry for ACI and NX-OS fabrics.
- NDI
- Node Dedicated IPEach Forcepoint firewall cluster node's own address, used for management and routing protocols.On this site: Firewall platforms
- NDO
- Nexus Dashboard OrchestratorOrchestrates policy across ACI Multi-Site fabrics; up to 500 ms RTT to APICs.
- NDP
- Neighbor Discovery ProtocolIPv6 replacement for ARP, built on ICMPv6.On this site: IP addressing and subnetting, Routing protocols
- NDR
- Network Detection and ResponseTools that watch network traffic for signs of attack and help the team respond.On this site: Security fundamentals
- NDR
- Next Data RateThe InfiniBand generation that runs at 400 Gb/s per port.On this site: AI infrastructure
- NET
- Network Entity TitleAn IS-IS router's address.
- NETCONF
- Network Configuration ProtocolModel driven configuration over SSH (RFC 6241).On this site: Switching and campus LAN
- NETCONF / RESTCONF
- Network Configuration Protocol / Its REST EquivalentModel driven device configuration over SSH (830) or HTTPS.
- NFR
- Non Functional RequirementAvailability, performance, security, recoverability and operability targets designs are judged against.
- NFS
- Network File SystemFile storage protocol, often used for VMware datastores.On this site: VXLAN EVPN and ACI, Private cloud and storage, Servers and virtualisation
- NGFW
- Next Generation FirewallStateful firewall plus application, user and threat inspection.On this site: Firewall platforms, Security fundamentals, Support and service management
- NH
- Next HopThe address a route points to; in EVPN it is the remote VTEP (or a border gateway VIP).
- NHRP
- Next Hop Resolution ProtocolDMVPN's address resolution: spokes register with the hub.On this site: Troubleshooting, WAN, MPLS and VPN
- NHS
- Next Hop ServerThe DMVPN hub that maps each spoke's tunnel address to its public address with NHRP.On this site: WAN, MPLS and VPN
- NIC
- Network Interface CardPhysical or virtual network adapter; vmnics on ESXi hosts.On this site: AI infrastructure, AWS, Azure and Google Cloud, Security
- NIOC
- Network I/O ControlVDS feature that shares uplink bandwidth by traffic type.
- NIS
- Network and Information SystemsUK regulations that set security duties for essential services and key digital services.On this site: Government and defence
- NIST
- National Institute of Standards and TechnologyUS standards body; runs the NVD.On this site: IoT and edge, Private cloud and storage, Servers and virtualisation
- NLB
- Network Load BalancerAWS layer 4 load balancer for TCP and UDP, with static IP addresses.On this site: Load balancing
- NLS
- NVIDIA License SystemServes licences for NVIDIA AI Enterprise and virtual GPU software.On this site: AI infrastructure, Home lab
- NMS
- Network Management SystemMonitoring platform such as SolarWinds.On this site: Support and service management
- NOC
- Network Operations CentreTeam that watches the network around the clock.On this site: SD-WAN and SDN, WAN, MPLS and VPN
- NON
- Non ConfirmableCoAP message type sent without asking for an acknowledgement.On this site: IoT and edge
- NOS
- Network Operating SystemThe switch software: NX-OS, EOS, SONiC, OS10.
- NPIV
- N_Port ID VirtualisationLets one FC port hold several fabric logins, for VMs or blades.On this site: Private cloud and storage
- NPL
- National Physical LaboratoryUK national time standard; a terrestrial UTC source for NTP and PTP.On this site: Government and defence
- NPM
- Network Performance MonitorSolarWinds tool for availability, utilisation and alerts.
- NPSA
- National Protective Security AuthorityUK authority for physical and personnel security of critical sites.On this site: Government and defence
- NQN
- NVMe Qualified NameUnique name of an NVMe host or subsystem, like an iSCSI IQN.On this site: Private cloud and storage
- NRZ / PAM4
- Non Return to Zero / 4 level Pulse Amplitude ModulationSignal encodings; PAM4 doubles bits per symbol for 100G lanes and above.
- NS
- Name Server RecordDNS record naming the servers for a zone.On this site: Networking fundamentals
- NS
- Neighbour SolicitationIPv6 neighbour discovery request for a neighbour's MAC address, also used to detect duplicate addresses.On this site: IP addressing and subnetting
- NSC
- Network Security ControlPCI DSS v4 term for firewalls and equivalent controls (Requirement 1).
- NSF
- Non Stop ForwardingKeeps forwarding during a supervisor switchover.
- NSG
- Network Security GroupAzure stateful filter on subnets and network interfaces.On this site: AWS, Azure and Google Cloud, Troubleshooting
- NSM
- Network Security ManagerSonicWall's central management platform.
- NSSA
- Not So Stubby AreaOSPF area that blocks external LSAs but allows local redistribution (type 7).On this site: Troubleshooting
- NSX
- VMware NSX (product name)VMware network virtualisation and distributed firewall.On this site: VXLAN EVPN and ACI, IP addressing and subnetting, Networking fundamentals
- NSX-T
- NSX-T Data CenterFormer name of today's VMware NSX; renamed from 4.0.0.1.On this site: Support and service management, VMware NSX
- NSX-V
- NSX Data Center for vSphereLegacy NSX tied to one vCenter, using VXLAN; end of general support 16 Jan 2022.On this site: VMware NSX
- NTA
- Network Traffic AnalysisvDefend security feature that spots suspicious traffic patterns.
- NTE
- Network Terminating EquipmentThe carrier's box at the customer site where its circuit ends.On this site: Troubleshooting
- NTP
- Network Time ProtocolTime sync on UDP 123; makes logs line up during incidents.On this site: Network automation, SD-Access campus fabric, VXLAN EVPN and ACI
- NTP / NTS
- Network Time Protocol / Network Time SecurityMillisecond clock sync over UDP 123; NTS authenticates it.
- NTS
- Network Time SecurityAdds authentication to NTP, so clients know the time came from the real server.On this site: Networking fundamentals, Troubleshooting
- NUMA
- Non Uniform Memory AccessMemory and PCIe devices are local to a socket; align workloads to it.On this site: Servers and virtualisation
- NVA
- Network Virtual ApplianceA firewall or router running as a virtual machine in a cloud network.On this site: AWS, Azure and Google Cloud
- NVE
- Network Virtualisation EdgeThe NX-OS interface (nve1) that acts as the VTEP.On this site: VXLAN EVPN and ACI, Troubleshooting
- NVGRE
- Network Virtualisation Using Generic Routing EncapsulationOlder Microsoft overlay, now rare.On this site: VXLAN EVPN and ACI
- NVL72 / NVL
- NVLink 72 GPU Domain (NVL means NVLink)GB200 NVL72: 72 GPUs in one NVLink domain, about 120 kW per rack.
- NVLink / NVSwitch
- NVIDIA GPU Interconnect / SwitchScale up GPU to GPU links inside a server or rack.
- NVMe
- Non Volatile Memory ExpressFlash native storage protocol with massive parallel queues.On this site: AI infrastructure, Design authority, Private cloud and storage
- NVMe-oF
- NVMe over FabricsNVMe extended across a network: TCP, RoCE or Fibre Channel.
- NVMe/RoCE / NVMe/FC
- NVMe over RoCE / over Fibre ChannelLowest latency Ethernet option / NVMe on an existing FC SAN.
- NVMe/TCP
- NVMe over TCPNVMe over standard Ethernet.On this site: Private cloud and storage, Troubleshooting
- NVO
- Network Virtualisation OverlayIETF term for overlays such as VXLAN EVPN (NVO3 working group).
- NVR
- Network Video RecorderRecords and stores IP camera streams.On this site: IoT and edge
- NX-API
- NX-OS Application Programming InterfaceREST and JSON RPC API on Nexus switches.On this site: Network automation, Troubleshooting
- NX-OS
- Nexus Operating SystemSoftware on Cisco Nexus and MDS switches.On this site: VXLAN EVPN and ACI, Data centre networks, Design authority
O
- OAM
- Operations, Administration and MaintenanceTools to test and monitor paths, such as BFD and link OAM.On this site: Troubleshooting, WAN, MPLS and VPN
- OASIS
- Organisation for the Advancement of Structured Information StandardsOwns the KMIP key management standard.On this site: Security
- OCI
- Open Container InitiativeStandard for container images and runtimes.
- OCP
- Open Compute ProjectOpen hardware designs for racks, power and liquid cooling (also OpenShift Container Platform).On this site: Data centre facilities
- OCSP
- Online Certificate Status ProtocolLive check of whether a certificate has been revoked.On this site: Security fundamentals, Security
- ODA
- Open Digital ArchitectureTM Forum blueprint for modular, cloud native telecoms IT.On this site: Network automation
- ODF
- Optical Distribution FrameRack panel where incoming fibres are terminated and patched.
- OEE
- Overall Equipment EffectivenessAvailability times performance times quality for a production line.On this site: Operational technology
- OEM
- Original Equipment ManufacturerThe vendor, for example Cisco, Fortinet, Palo Alto or Broadcom.
- OFDM
- Orthogonal Frequency Division MultiplexingSplits a channel into many narrow subcarriers sent in parallel; the basis of modern Wi-Fi and 4G.On this site: Wireless and mobile
- OFDMA
- Orthogonal Frequency Division Multiple AccessOFDM shared between users, so several clients send in one transmission; added in Wi-Fi 6.On this site: Wireless and mobile
- OID
- Object IdentifierThe address of one value in an SNMP MIB.
- OIDC
- OpenID ConnectSign in layer on OAuth 2.0 that tells an app who the user is.On this site: Network automation, Troubleshooting
- OIDC / SAML
- OpenID Connect / Security Assertion Markup LanguageFederated login standards for SSO.
- OKC
- Opportunistic Key CachingLets a client reuse its key when roaming between access points on the same controller.On this site: Wireless and mobile
- OLA
- Operational Level AgreementInternal agreement between teams that underpins the SLA to the customer.On this site: Support and service management
- OLTS
- Optical Loss Test SetLight source and power meter pair that measures the end to end loss of a fibre link.On this site: Data centre facilities
- OLTS / OTDR
- Optical Loss Test Set / Optical Time Domain ReflectometerFibre test tools for loss certification and fault finding.
- OM3 / OM4 / OM5
- Optical Multimode Grades 3, 4 and 5Multimode fibre; SR optics reach about 70 m on OM3 and 100 m on OM4.
- OMP
- Overlay Management ProtocolCatalyst SD-WAN control protocol between controllers and edges.On this site: SD-WAN and SDN, Troubleshooting
- OOB
- Out of BandSeparate management path with console servers, used when production is down.On this site: Data centre networks, Resilience, risk and cost, Troubleshooting
- OPA
- Open Policy AgentPolicy as code engine (Rego language) to check changes in pipelines.On this site: Troubleshooting
- OpEx
- Operating ExpenditureOngoing cost: licences, support, power, space and people.
- OS
- Operating SystemHost or guest software such as RHEL or Windows Server.On this site: Firewall platforms, Security, Troubleshooting
- OS10
- Dell SmartFabric OS10Dell PowerSwitch network operating system.On this site: Data centre networks
- OS2
- Optical Singlemode Grade 2Standard singlemode fibre for DR, FR, LR and DWDM optics.On this site: Data centre facilities, Networking fundamentals
- OSFP
- Octal Small Form Factor Pluggable8 lane pluggable for 400G and 800G.
- OSI
- Open Systems InterconnectionThe seven layer reference model used to locate faults.On this site: Networking fundamentals, Security fundamentals
- OSPF
- Open Shortest Path FirstOpen standard link state protocol; AD 110; one of the Tier-0 peering options.On this site: SD-Access campus fabric, VXLAN EVPN and ACI, Data centre networks
- OSPFv3
- OSPF Version 3OSPF for IPv6 (and IPv4 with address families).On this site: Routing protocols
- OSS
- Operations Support SystemsTelecoms systems for inventory, provisioning, faults and performance.On this site: Network automation
- OSS / BSS
- Operations Support Systems / Business Support SystemsTelco management stacks.
- OT
- Operational TechnologySystems that monitor and control physical processes, such as PLCs and SCADA.On this site: AI infrastructure, SD-Access campus fabric, Cloud architecture
- OTA
- Over the AirFirmware or settings pushed to devices over their wireless link.On this site: Troubleshooting
- OTDR
- Optical Time Domain ReflectometerSends pulses down a fibre and plots the reflections to find breaks, splices and bad connectors.On this site: Data centre facilities
- OTV
- Overlay Transport VirtualisationNexus 7000 layer 2 extension between data centres.On this site: VXLAN EVPN and ACI, Data centre networks, Support and service management
- OU
- Organisational UnitActive Directory container for users and computers, used to apply group policy and delegate admin rights.On this site: Servers and virtualisation
- OUI
- Organisationally Unique IdentifierFirst 24 bits of a MAC address; identifies the maker.On this site: Networking fundamentals, Troubleshooting
- OVF/OVA
- Open Virtualisation Format / Open Virtual AppliancePackage formats used to deploy NSX Manager and Edge VMs.
- OVN
- Open Virtual NetworkVirtual networking for Open vSwitch, used by OpenStack and OpenShift.On this site: Private cloud and storage
- OVN / OVS
- Open Virtual Network / Open vSwitchSoftware switching and overlay behind OVN Kubernetes.
- OWASP
- Open Worldwide Application Security ProjectOpen community that publishes web security guidance, including the OWASP Top 10.On this site: Load balancing
P
- P2P
- Point to PointA routed link between two devices, addressed with a /31 in the fabric.
- PaaS
- Platform as a ServiceCloud platform that runs your code or database while the provider manages the servers and operating system.On this site: Cloud architecture
- PAgP
- Port Aggregation ProtocolOlder Cisco bundle negotiation; also used for VSS dual active detection.On this site: Switching and campus LAN, Troubleshooting
- PAM
- Privileged Access ManagementControls, records and time limits admin access.On this site: Data centre networks, Resilience, risk and cost, Security
- PAN
- Policy Administration NodeThe Cisco ISE persona where admins set policy, with one primary and one secondary.On this site: SD-Access campus fabric, Security
- PAN
- Primary Account NumberThe card number; where PAN is stored or processed defines the PCI DSS CDE.On this site: SD-Access campus fabric, Firewall platforms, Security
- PAN-OS
- Palo Alto Networks Operating SystemSoftware on Palo Alto firewalls; 12.1 released August 2025.On this site: Firewall platforms, Security, Troubleshooting
- PAT
- Port Address TranslationMany hosts share one address, told apart by source port.On this site: Firewall platforms, Networking fundamentals
- PAW
- Privileged Access WorkstationHardened workstation for admin access.On this site: Security
- PBF
- Policy Based ForwardingPalo Alto's version of policy based routing.
- PBKDF2
- Password Based Key Derivation Function 2Slows password guessing by hashing many thousands of times with a salt.On this site: Security fundamentals, Security
- PBR
- Policy Based Redirect (ACI)Steers selected traffic through firewalls or load balancers in a Cisco ACI fabric, without changing the routing table.On this site: VXLAN EVPN and ACI
- PBR
- Policy Based RoutingForwards chosen traffic by policy; invisible in show ip route.
- PC
- Personal ComputerA desktop or laptop.On this site: IP addressing and subnetting, Networking fundamentals, Troubleshooting
- PCAP
- Packet Capture (file format)The file Wireshark reads; handle it as sensitive data.
- PCI
- Payment Card IndustryCard schemes' security body.On this site: Troubleshooting, VMware NSX
- PCI DSS
- Payment Card Industry Data Security StandardV4.0.1 is current; CDE segmentation is the main design lever.On this site: Data centre facilities, Data centre networks, Design authority
- PCI SSC
- PCI Security Standards CouncilThe body that owns PCI DSS.
- PCIe
- Peripheral Component Interconnect ExpressServer expansion bus for NICs, GPUs and NVMe drives (Gen5 and Gen6).On this site: AI infrastructure, Servers and virtualisation
- PCP
- Priority Code PointThe 3 bit priority field in the 802.1Q tag (802.1p).On this site: Networking fundamentals
- PDC
- Primary Domain ControllerToday the PDC emulator FSMO role, which also leads time for the domain.On this site: Servers and virtualisation
- PDL
- Permanent Device LossvSphere state where the array reports that a storage device is gone for good.On this site: Servers and virtualisation
- PDU
- Power Distribution UnitRack power strip; dual feeds for dual PSUs. Also Protocol Data Unit.On this site: AI infrastructure
- PDU
- Protocol Data UnitThe unit of data at a layer: frame, packet or segment. Also Power Distribution Unit.On this site: Switching and campus LAN
- PDU / rPDU
- Power Distribution Unit / Rack PDUDistributes power to devices in the rack on A and B feeds.
- PE
- Provider EdgeProvider router holding customer VRFs in an MPLS VPN.On this site: Troubleshooting, WAN, MPLS and VPN, Home lab
- PEAP
- Protected EAPBuilds a TLS tunnel from the server certificate, then runs a password method such as MSCHAPv2 inside it.On this site: SD-Access campus fabric, Security, Wireless and mobile
- PF
- Power FactorRatio of real power (kW) to apparent power (kVA).
- PFAS
- Per and polyfluoroalkyl substancesChemicals facing restrictions that affect some fire suppression and immersion fluids.On this site: Data centre facilities
- PFC
- Priority Flow ControlPer class pause that makes a traffic class lossless (802.1Qbb).On this site: AI infrastructure, Private cloud and storage, Troubleshooting
- PFS
- Perfect Forward SecrecyFresh Diffie-Hellman keys for each IPsec SA; must match both ends.On this site: Security fundamentals, Troubleshooting
- PHP
- Penultimate Hop PoppingThe second last MPLS router removes the label, so the last router does only an IP lookup.On this site: WAN, MPLS and VPN
- PIM
- Protocol Independent MulticastBuilds multicast trees between routers, usually sparse mode with a rendezvous point.On this site: VXLAN EVPN and ACI, Networking fundamentals, Routing protocols
- PIN
- Personal Identification NumberSecond factor with an access card at data hall doors.
- PIR
- Post Implementation ReviewReview after a change or major incident to confirm results and capture lessons.On this site: Troubleshooting
- PIR
- Post Incident ReviewLearning review after an incident; feeds design changes.On this site: Troubleshooting
- PKI
- Public Key InfrastructureCertificates, CAs and keys that prove identity for VPNs, ISE and HTTPS.On this site: IoT and edge, Security fundamentals, Security
- PLC
- Programmable Logic ControllerRugged computer that runs the control logic for machines on a plant floor.On this site: IoT and edge, Operational technology
- PM
- Project Manager or Programme ManagerThe person who owns delivery, plan and budget.On this site: Troubleshooting
- PMF
- Protected Management Frames802.11w; signs management frames such as deauthentication so they cannot be spoofed. Required in WPA3.On this site: Wireless and mobile
- PMK
- Pairwise Master KeyThe key from 802.1X or a passphrase that the four way handshake turns into session keys.On this site: Wireless and mobile
- PMSI
- Provider Multicast Service InterfaceEVPN attribute saying whether BUM uses ingress replication or multicast.
- PMTUD
- Path MTU DiscoveryFinds the smallest MTU on a path using ICMP; broken if ICMP is blocked.On this site: Troubleshooting, WAN, MPLS and VPN
- pNFS
- Parallel NFSNFS 4.1 extension where clients read and write to the data servers directly, in parallel.
- POAP
- PowerOn Auto ProvisioningCisco NX-OS zero touch provisioning.On this site: Network automation
- PoC
- Proof of ConceptA small build that tests whether an idea works before committing to it.
- PoE
- Power over EthernetPowers phones, access points and cameras from the switch port.On this site: SD-Access campus fabric, Networking fundamentals, Operational technology
- PoE+
- Power over Ethernet PlusIEEE 802.3at, up to 30 W at the switch port; enough for most phones and access points.On this site: IoT and edge, Wireless and mobile
- POP3
- Post Office Protocol Version 3Downloads mail from the server to one client, on TCP 110, or 995 with TLS.On this site: Networking fundamentals
- PPM
- Planned Preventive MaintenanceScheduled, recorded maintenance of all systems.On this site: Support and service management, Troubleshooting
- PPN
- Procurement Policy NoteCabinet Office guidance for public buyers, such as PPN 014 on Cyber Essentials.On this site: Government and defence
- PPPoE
- Point to Point Protocol over EthernetCarries a PPP login session over Ethernet, as on many broadband lines.On this site: Networking fundamentals, WAN, MPLS and VPN
- PR
- Pull RequestA proposed change in Git, reviewed and tested before merge.On this site: Troubleshooting
- PRA
- Prudential Regulation AuthorityPart of the Bank of England; operational resilience SS1/21 and outsourcing SS2/21.On this site: Design authority, Resilience, risk and cost
- PRF
- Pseudo Random FunctionStretches a key into more key material; used in TLS and IKE.On this site: Security fundamentals, WAN, MPLS and VPN
- PRINCE2
- PRojects IN Controlled EnvironmentsProject management method.On this site: Design authority, Government and defence, Resilience, risk and cost
- PROD / NONPROD / MGMT
- Production / Non Production / ManagementZone labels used in segmentation designs.
- PS21/3
- FCA Policy Statement 21/3Building operational resilience: important business services, impact tolerances, mapping and testing.On this site: Design authority
- PS24/16
- FCA Policy Statement 24/16Rules for the UK critical third parties regime, in force from 1 January 2025.
- PS26/2
- FCA Policy Statement 26/2Operational incident and third party reporting; published 18 March 2026, in force 18 March 2027.
- PS7/26
- PRA Policy Statement 7/26The PRA's matching rules for incident and third party reporting alongside FCA PS26/2.
- PSIRT
- Product Security Incident Response TeamEach vendor's security advisory team; Cisco bundles on fixed Wednesdays.On this site: SD-Access campus fabric, VXLAN EVPN and ACI, SD-WAN and SDN
- PSK
- Pre Shared KeyShared secret for IKE authentication; certificates are stronger.On this site: Troubleshooting
- PSN
- Policy Service NodeISE node that answers RADIUS and TACACS+ requests.On this site: SD-Access campus fabric, Security
- PSU
- Power Supply UnitCheck PSU status during PPM; dual PSUs on separate feeds.On this site: Troubleshooting
- PTP
- Precision Time ProtocolIEEE 1588 sub microsecond time sync; MiFID II timestamping.On this site: Data centre networks, Design authority, Networking fundamentals
- PUE
- Power Usage EffectivenessFacility power divided by IT power; industry average about 1.54 (Uptime 2025).On this site: AI infrastructure, Data centre facilities, Resilience, risk and cost
- PVID
- Port VLAN IDThe VLAN that untagged frames join on a port.On this site: Troubleshooting
- PVLAN
- Private VLANIsolates hosts within one subnet; promiscuous port to the gateway.
- PVST
- Per VLAN Spanning TreeCisco spanning tree with one instance per VLAN.On this site: Switching and campus LAN
- PVST+
- Per VLAN Spanning Tree PlusCisco's per VLAN version of classic 802.1D spanning tree.On this site: Switching and campus LAN
- PXE
- Preboot Execution EnvironmentNetwork boot for automated server builds.On this site: Data centre networks, Private cloud and storage, Troubleshooting
- PXN
- PCIe X NVLinkNCCL feature that routes traffic through NVLink to the best NIC rail.
- pyATS
- Python Automated Test SystemsCisco's network testing framework for pre and post change checks.On this site: Network automation, VXLAN EVPN and ACI, Design authority
Q
- QAM
- Quadrature Amplitude ModulationEncodes bits in a signal's amplitude and phase; 4096 QAM in Wi-Fi 7 carries 12 bits per symbol.On this site: Wireless and mobile
- QEMU
- Quick EmulatorOpen source machine emulator that, with KVM, runs virtual machines on Linux.On this site: Servers and virtualisation
- QinQ
- 802.1Q in 802.1Q (IEEE 802.1ad)Double tagging used by carriers to carry customer VLANs.On this site: WAN, MPLS and VPN
- QLC / TLC
- Quad Level Cell / Triple Level CellFlash types; QLC is denser and cheaper per TB.
- QoS
- Quality of ServiceClassifies, marks and queues traffic so critical flows go first.On this site: SD-Access campus fabric, Data centre networks, IoT and edge
- QSA
- Qualified Security AssessorAssesses PCI DSS compliance and must accept the segmentation evidence.
- QSFP / QSFP28 / QSFP56 / QSFP112 / QSFP-DD
- Quad Small Form Factor Pluggable (and its speed variants; DD means double density)40G, 100G, 200G, 400G per lane group; QSFP-DD reaches 400G and 800G.
R
- R&S
- Routing and SwitchingCisco certification track name (CCNP R&S, CCIE R&S written).On this site: Home lab
- RA
- Router AdvertisementIPv6 message announcing gateways and prefixes; RA guard blocks rogue ones.On this site: IP addressing and subnetting, Troubleshooting
- RACI
- Responsible, Accountable, Consulted, InformedMatrix that makes ownership clear between resolver groups and suppliers.On this site: Data centre networks, Firewall platforms, Operational technology
- RADIUS
- Remote Authentication Dial In User ServiceNetwork access AAA on UDP 1812 and 1813: 802.1X, MAB and VPN.On this site: SD-Access campus fabric, IoT and edge, Networking fundamentals
- RadSec
- RADIUS over TLSEncrypts RADIUS traffic between devices and servers.On this site: Security fundamentals
- RAG
- Retrieval Augmented GenerationAI pattern combining an LLM with search over company data.
- RAID
- Redundant Array of Independent DisksSpreads data over several disks with mirroring or parity, so one failed disk loses nothing.On this site: Private cloud and storage, IoT and edge, Servers and virtualisation
- RAID
- Risks, Assumptions, Issues and DependenciesLog kept on CR and refresh projects to track what could go wrong.
- RAID (storage)
- Redundant Array of Independent DisksDrive level protection by mirroring or parity; not a backup.
- RAM
- Random Access MemoryServer memory; sized per VM and container density.On this site: Home lab
- RAN
- Radio Access NetworkMobile network edge.On this site: Network automation, Design authority
- Rapid PVST+
- Rapid Per VLAN Spanning Tree PlusCisco's per VLAN RSTP; the default mode on Nexus.On this site: Switching and campus LAN
- RARP
- Reverse Address Resolution ProtocolOld protocol mapping MAC to IP; vMotion uses RARP frames to update switches.On this site: Servers and virtualisation
- RBAC
- Role Based Access ControlRights go to roles and people get roles, rather than rights set person by person.
- RCA
- Root Cause AnalysisEvidence based investigation into why an incident happened.On this site: Troubleshooting
- RD
- Route Distinguisher64 bit value that makes customer routes unique in MP-BGP.On this site: VXLAN EVPN and ACI, Troubleshooting, WAN, MPLS and VPN
- RDHx
- Rear Door Heat ExchangerChilled water coil on the rack door for higher density air cooled racks.
- RDMA
- Remote Direct Memory AccessMoves data between memories without involving the CPUs.On this site: AI infrastructure, Networking fundamentals
- RDNSS
- Recursive DNS Server OptionRouter advertisement option that tells IPv6 hosts which DNS servers to use, with no DHCPv6 server needed.On this site: IP addressing and subnetting
- RDP
- Remote Desktop ProtocolWindows remote access protocol.On this site: Networking fundamentals, Troubleshooting
- RDS
- Relational Database ServiceAWS managed databases such as PostgreSQL, MySQL and SQL Server.On this site: AWS, Azure and Google Cloud
- RDY
- Ready (%RDY)ESXi esxtop metric: time a vCPU is ready to run but waiting for a physical CPU.On this site: Servers and virtualisation, Troubleshooting
- RE
- Routing EngineThe Juniper control plane card that runs routing protocols and management.On this site: Troubleshooting
- REP
- Resilient Ethernet ProtocolCisco ring protocol that blocks one port and reconverges faster than spanning tree when a link fails.On this site: SD-Access campus fabric, Troubleshooting
- REST
- Representational State TransferAPI style over HTTPS used by NSX and firewall managers.On this site: Network automation, VXLAN EVPN and ACI, Servers and virtualisation
- RF
- Radio FrequencyThe radio side of wireless: channels, power, interference and coverage.On this site: Wireless and mobile
- RFC
- Request for ChangeITIL's formal change proposal. Same letters as the IETF Request for Comments.On this site: Support and service management
- RFC
- Request for CommentsIETF standards documents, such as RFC 1918 private addressing.On this site: IP addressing and subnetting
- RFI / RFP / RFQ
- Request for Information / Proposal / QuotationFormal stages of vendor and technology evaluation.
- RHEL / RHCOS
- Red Hat Enterprise Linux / Red Hat Enterprise Linux CoreOSRed Hat's server OS and OpenShift's immutable node OS.
- RIB
- Routing Information BaseThe routing table built from all sources.On this site: Routing protocols, Troubleshooting
- RID
- Relative IdentifierThe last part of a Windows security identifier, unique to one user or group in a domain.On this site: Servers and virtualisation
- RID
- Router IDUnique ID for OSPF or BGP; duplicates cause flapping.On this site: Servers and virtualisation
- RIP
- Routing Information ProtocolOld distance vector protocol; AD 120.On this site: IP addressing and subnetting, Routing protocols
- RIPE
- Réseaux IP EuropéensEuropean IP networks community; RIPE NCC runs the regional internet registry.On this site: VXLAN EVPN and ACI, Data centre networks, IP addressing and subnetting
- RIPE NCC
- Réseaux IP Européens Network Coordination CentreEurope's regional internet registry; you managed IP space and ROAs with it at Manx Telecom.On this site: VXLAN EVPN and ACI, Data centre networks, IP addressing and subnetting
- RIR
- Regional Internet RegistryAllocates IP addresses and AS numbers by region.On this site: Routing protocols, Security
- RLOC
- Routing LocatorIn LISP and SD-Access, the address of the fabric switch an endpoint sits behind.On this site: SD-Access campus fabric
- RMA
- Return Material AuthorisationVendor process to replace failed hardware.On this site: Troubleshooting
- RMA
- Return Merchandise AuthorisationVendor process to replace failed hardware.On this site: Troubleshooting
- RMAC
- Router MACThe MAC of a leaf used as the inner destination MAC for routed (symmetric IRB) VXLAN traffic.
- RNR
- Reduced Neighbour ReportLets an access point list its other radios, so 6 GHz clients find them without probing.On this site: Wireless and mobile
- ROA
- Route Origin AuthorisationSigned record of which AS may originate a prefix; used with RPKI.On this site: Routing protocols
- ROADM
- Reconfigurable Optical Add Drop MultiplexerAdds or drops DWDM wavelengths at a node without manual patching.On this site: WAN, MPLS and VPN
- RoCE
- RDMA over Converged EthernetRemote direct memory access over Ethernet, which needs lossless queues with PFC and ECN.On this site: Private cloud and storage, Troubleshooting
- RoCE / RoCEv2
- RDMA over Converged Ethernet (version 2)RDMA over routed Ethernet on UDP 4791.
- RoCEv2
- RDMA over Converged Ethernet Version 2Routable RoCE over UDP and IP; the usual choice for GPU back end networks.On this site: Networking fundamentals
- RODC
- Read Only Domain ControllerDomain controller with a read only copy of the directory, for branch sites with weak physical security.On this site: Servers and virtualisation
- RoI
- Register of InformationDORA register of all ICT third party arrangements.
- ROMMON
- ROM MonitorCisco boot loader used for recovery; tampering was part of the ArcaneDoor attacks.
- RP
- Rendezvous PointMeeting point for PIM sparse mode multicast trees.On this site: Routing protocols, Troubleshooting
- RP
- Root PortThe port on each switch with the best path to the root bridge. Also PIM Rendezvous Point.On this site: VXLAN EVPN and ACI, Routing protocols, Switching and campus LAN
- RPC
- Remote Procedure CallOne program calling a function in another over the network.On this site: Troubleshooting
- RPF
- Reverse Path ForwardingCheck that traffic arrived on the interface towards its source; used by multicast and uRPF.On this site: Routing protocols, Troubleshooting
- RPKI
- Resource Public Key InfrastructureValidates BGP route origins.On this site: IP addressing and subnetting, Routing protocols, Security
- RPO
- Recovery Point ObjectiveThe most data, measured in time, the business can afford to lose.On this site: Private cloud and storage, Resilience, risk and cost
- RPO / RTO
- Recovery Point Objective / Recovery Time ObjectiveHow much data can be lost / how long a service can be down.
- RPP
- Remote Power PanelPower distribution cabinet near the racks, fed from the main PDU.
- RPR
- Route Processor RedundancyCisco standby supervisor mode that is only partly booted, so failover is slower than SSO.On this site: Troubleshooting
- RR
- Route ReflectoriBGP router that reflects routes so a full mesh is not needed. Also Round Robin.On this site: Troubleshooting
- RRM
- Radio Resource ManagementController function that sets access point channels and transmit power automatically.On this site: Wireless and mobile
- RS
- Reed SolomonErasure coding scheme, for example RS(6,3).On this site: Private cloud and storage
- RS
- Router SolicitationIPv6 message a host sends to ask routers for an advertisement straight away.On this site: IP addressing and subnetting
- RSA
- Rivest, Shamir and AdlemanPublic key algorithm; SSH keys of at least 2048 bits.On this site: Security fundamentals
- RSPAN
- Remote SPANMirrors traffic across switches over a dedicated VLAN.On this site: Switching and campus LAN, Troubleshooting
- RSSI
- Received Signal Strength IndicatorHow strong a radio signal is at the receiver, in dBm.On this site: IoT and edge, Troubleshooting, Wireless and mobile
- RSTP
- Rapid Spanning Tree ProtocolIEEE 802.1w; converges in about a second with a handshake.On this site: Operational technology, Switching and campus LAN
- RT
- Route TargetBGP extended community that controls VRF route import and export.On this site: VXLAN EVPN and ACI, WAN, MPLS and VPN
- RT 1 to RT 5
- EVPN Route Types 1 to 5Shorthand for EVPN route types: RT 2 MAC/IP, RT 3 IMET, RT 5 IP prefix.
- RTEP
- Remote Tunnel EndpointEdge endpoint that carries traffic between Federation sites.
- RTO
- Recovery Time ObjectiveHow long a service can be down before recovery must be complete.On this site: Private cloud and storage, Resilience, risk and cost
- RTS
- Regulatory Technical StandardsDetailed EU rules under DORA and MiFID II, for example RTS 25 on clock accuracy.On this site: Resilience, risk and cost
- RTSP
- Real Time Streaming ProtocolControls video streams from IP cameras, on TCP 554.On this site: IoT and edge
- RTT
- Round Trip TimeLatency there and back; sets limits such as 50 ms for ACI Multi-Pod.On this site: Troubleshooting
- RU / U
- Rack Unit1.75 inches (44.45 mm) of rack height.
S to Z
Terms from S to Z
S
- S3
- Simple Storage Service (API)De facto object storage API; Object Lock gives immutability.On this site: AWS, Azure and Google Cloud, Private cloud and storage
- SA
- Security AssociationOne direction of an agreed IPsec or IKE tunnel. Also Solutions Architect.On this site: Firewall platforms, Security fundamentals, Troubleshooting
- SaaS
- Software as a ServiceFinished applications delivered over the internet, such as Microsoft 365.On this site: Cloud architecture, Troubleshooting, WAN, MPLS and VPN
- SACM
- Service Asset and Configuration ManagementITIL practice that maintains the CMDB; a SACM team is advertised at the same site.
- SAE
- Simultaneous Authentication of EqualsWPA3 Personal handshake that resists offline password guessing.On this site: Wireless and mobile
- SAML
- Security Assertion Markup LanguageXML standard for single sign on between an identity provider and an application.On this site: Security, WAN, MPLS and VPN
- SAN
- Storage Area NetworkDedicated block storage network with two fabrics and zoning.On this site: Servers and virtualisation
- SAS
- Serial Attached SCSIDrive interface used in older servers and arrays.On this site: Data centre networks
- SASE
- Secure Access Service EdgeCloud delivered network security and access.On this site: SD-WAN and SDN, Security fundamentals, Security
- SAT
- Site Acceptance TestTests run on site after installation.On this site: Data centre facilities
- SBOM
- Software Bill of MaterialsList of software components in a product; helps vulnerability management.
- SC
- Security CheckUK national security vetting for regular access to SECRET material.On this site: Government and defence
- SCADA
- Supervisory Control and Data AcquisitionCentral monitoring and control of remote plant such as pumps and substations.On this site: IoT and edge, Operational technology
- SCEP
- Simple Certificate Enrollment ProtocolOlder protocol for devices to request certificates, still common in device management and network kit.On this site: SD-Access campus fabric, Security, Troubleshooting
- SCP
- Secure Copy ProtocolFile copy over SSH; a safe way to move images and backups.On this site: Troubleshooting
- SCSI
- Small Computer System InterfaceOlder block command set carried by FC and iSCSI.On this site: Private cloud and storage
- SD-WAN
- Software Defined Wide Area NetworkController driven WAN overlay.On this site: Load balancing, Network automation, SD-Access campus fabric
- SDA
- Software Defined AccessCisco campus fabric with Catalyst Centre.
- SDDC
- Software Defined Data CenterVMware term for compute, storage and network in software (VCF).
- SDN
- Software Defined NetworkingCentral software control of the network; NSX, ACI and SD-WAN are examples.On this site: Load balancing, Cloud architecture, Design authority
- SET
- Switch Embedded TeamingHyper-V network card teaming built into the virtual switch.On this site: Servers and virtualisation
- sFlow
- Sampled FlowPacket sampling telemetry standard.On this site: Network automation, VXLAN EVPN and ACI, Data centre networks
- SFP
- Small Form Factor PluggableOptical or copper transceiver module; check light levels when links flap.On this site: Networking fundamentals
- SFP / SFP28
- Small Form Factor Pluggable (25G variant)Single lane optics for 10G and 25G server links.
- SFTP
- SSH File Transfer ProtocolFile transfer over SSH; NSX Manager backups go to an SFTP server.On this site: Networking fundamentals, VMware NSX
- SGACL
- Scalable Group ACLTrustSec rule that permits or denies traffic between two security group tags.On this site: SD-Access campus fabric
- SGT
- Security Group TagCisco TrustSec group label used for group based policy.On this site: SD-Access campus fabric, SD-WAN and SDN, IoT and edge
- SHA
- Secure Hash AlgorithmHash family for integrity; SHA 2 for IPsec and image checks.On this site: Security fundamentals, Security
- SHARP
- Scalable Hierarchical Aggregation and Reduction ProtocolIn network computing for InfiniBand collectives.On this site: AI infrastructure
- SIAM
- Service Integration and ManagementModel where one integrator manages several suppliers as one service.On this site: Support and service management
- SIEM
- Security Information and Event ManagementCollects and correlates logs; network devices feed it.On this site: SD-Access campus fabric, VXLAN EVPN and ACI, Data centre networks
- SIG
- Secure Internet GatewayCloud service that filters users' web and DNS traffic.On this site: Troubleshooting
- SIM
- Subscriber Identity ModuleCard or embedded chip that identifies a device to a mobile network.On this site: Wireless and mobile
- SIP
- Session Initiation ProtocolVoice and video call signalling.On this site: Firewall platforms, Networking fundamentals, Troubleshooting
- SIS
- Safety Instrumented SystemIndependent control system that takes a process to a safe state when limits are breached.On this site: Operational technology
- SISF
- Switch Integrated Security FeaturesCisco device tracking framework behind IPv6 first hop security.On this site: SD-Access campus fabric
- SKU
- Stock Keeping UnitA specific orderable part number; pod BOMs are built from SKUs.
- SL
- Security LevelIEC 62443 target from 1 to 4 for how strong a zone's defences must be.On this site: Operational technology
- SLA
- Service Level AgreementTargets agreed with the customer; resolve issues within SLA, escalate before a breach.On this site: Network automation, Resilience, risk and cost, Routing protocols
- SLAAC
- Stateless Address AutoconfigurationIPv6 hosts build their own address from the router's prefix.On this site: IP addressing and subnetting
- SLO
- Service Level ObjectiveThe internal target that sits behind an SLA.On this site: Resilience, risk and cost
- SM
- Subnet ManagerInfiniBand control plane that assigns LIDs and computes forwarding.
- SMA
- Secure Mobile AccessSonicWall remote access appliances; the SMA 100 had a 2025 rootkit campaign.
- SMB
- Server Message BlockWindows file sharing protocol.On this site: Networking fundamentals, Private cloud and storage, Servers and virtualisation
- SMC
- Security Management CentreForcepoint NGFW console where policies are built and uploaded.On this site: Firewall platforms, Support and service management
- SME
- Subject Matter ExpertThe person with deep knowledge of one area.
- SMET
- Selective Multicast Ethernet TagEVPN route type 6, for optimised multicast.
- SMF
- Session Management Function5G core function that sets up data sessions and picks the UPF.On this site: Wireless and mobile
- SMS
- Short Message ServiceText message codes; a weak second factor.
- SMT
- Simultaneous MultithreadingTwo threads per CPU core; affects performance and licence counting.
- SMTP
- Simple Mail Transfer ProtocolMoves email between mail servers on TCP 25, with 587 for mail sent from clients.On this site: Networking fundamentals
- SMU
- Software Maintenance UpgradeCisco point patch for a specific bug or advisory.On this site: Support and service management
- SNAT
- Source NATRewrites the source address, for example to hide inside hosts.On this site: VMware NSX, Load balancing
- SNI
- Server Name IndicationThe host name a client sends in the TLS Client Hello, so one IP address can serve many certificates.On this site: Load balancing, Networking fundamentals, Troubleshooting
- SNMP
- Simple Network Management ProtocolMonitoring on UDP 161 and traps on 162; use version 3 in secure estates.On this site: Network automation, SD-Access campus fabric, Networking fundamentals
- SNMP / SNMPv3
- Simple Network Management Protocol (version 3)Poll and trap monitoring.
- SNMPv3
- SNMP Version 3Adds users, authentication and encryption; run it at authPriv.On this site: Network automation, Security fundamentals, Security
- SNR
- Signal to Noise RatioHow far a signal sits above the noise floor, in dB; Wi-Fi needs about 25 dB for high data rates.On this site: Troubleshooting, Wireless and mobile
- SOA
- Start of AuthorityDNS record holding zone serial and timers.On this site: Networking fundamentals
- SOAR
- Security Orchestration, Automation and ResponseRuns security playbooks automatically, such as isolating a host after an alert.On this site: Security fundamentals
- SOC
- Security Operations CentreTeam that monitors the SIEM and responds to security alerts.On this site: Security fundamentals, Security
- SOC 2
- System and Organisation Controls 2An assurance report on a supplier's controls, used in third party due diligence.On this site: Government and defence
- SONiC
- Software for Open Networking in the CloudOpen source network OS; one lever for lock in avoidance.On this site: AI infrastructure, Data centre networks, Home lab
- SOP
- Standard Operating ProcedureWritten step by step method for routine tasks and standard changes.
- SoT
- Source of TruthAuthoritative intended state that automation reads from, for example NetBox.
- SoW
- Statement of WorkDefines the scope and deliverables of an engagement.
- SP
- Special Publication (NIST)As in NIST SP 800 88 or SP 800 207: numbered NIST guidance documents.On this site: AI infrastructure, Private cloud and storage, Home lab
- SP 800 207
- NIST Special Publication 800 207The zero trust architecture reference.
- SP3
- Single Pass Parallel ProcessingPalo Alto design: each packet is classified once by all engines.
- SPAN
- Switched Port AnalyserMirrors ports or VLANs to a capture port.On this site: VXLAN EVPN and ACI, Switching and campus LAN, Troubleshooting
- SPF
- Sender Policy FrameworkDNS record that lists which servers may send mail for a domain.On this site: Networking fundamentals
- SPF
- Shortest Path FirstDijkstra calculation used by OSPF and IS-IS.On this site: Routing protocols, Troubleshooting
- SPI
- Security Parameters IndexNumber that identifies an IPsec SA in each ESP packet.On this site: Security fundamentals
- SPIFFE
- Secure Production Identity Framework For EveryoneStandard for workload identities in zero trust designs.
- SQL
- Structured Query LanguageDatabase query language; databases often run on bare metal pods.On this site: Load balancing, Firewall platforms, IoT and edge
- SR
- Segment RoutingSource routing using MPLS labels or IPv6. Also NSX Service Router.
- SR
- Service RouterPart of an NSX gateway on the Edge for uplinks and stateful services. Also Segment Routing.On this site: Troubleshooting, VMware NSX
- SR / SR4 / SR8
- Short Reach Multimode (4 or 8 lanes)Multimode optics, about 70 to 100 m.
- SR / SRv6
- Segment Routing / Segment Routing over IPv6Source routing for WAN and DCI traffic engineering (SR also means short reach optics).
- SR-IOV / IOV
- Single Root I/O VirtualisationSplits a NIC into virtual functions for near bare metal VM networking.
- SRLG
- Shared Risk Link GroupLinks that share a duct or fibre path and fail together; key to true DCI diversity.
- SRTT
- Smoothed Round Trip TimeA running average of round trip time that TCP uses to set its retransmit timer.On this site: Troubleshooting
- SRV
- Service LocatorDNS record that gives the host and port for a service, such as Active Directory LDAP.On this site: Servers and virtualisation
- SRX
- Juniper SRX Series (a product name, not an expansion)Juniper's zone based firewall line running Junos.On this site: Firewall platforms, Security, Support and service management
- SS1/21
- PRA Supervisory Statement 1/21Operational resilience: impact tolerances for important business services.On this site: Design authority
- SS2/21
- PRA Supervisory Statement 2/21Outsourcing and third party risk management expectations.On this site: Resilience, risk and cost
- SSD
- Solid State DriveFlash storage device, usually NVMe in new servers.On this site: Home lab
- SSDP
- Simple Service Discovery ProtocolUPnP discovery over multicast on UDP 1900; often abused for reflection attacks.On this site: IoT and edge, Troubleshooting
- SSE
- Security Service EdgeCloud web gateway, CASB and zero trust access together; SASE without the SD-WAN part.On this site: Troubleshooting
- SSH
- Secure ShellEncrypted CLI access on TCP 22; version 2 only.On this site: Network automation, Data centre networks, Firewall platforms
- SSID
- Service Set IdentifierThe wireless network name.On this site: SD-Access campus fabric, Troubleshooting
- SSL
- Secure Sockets LayerOld name for TLS; all SSL versions are deprecated.On this site: Load balancing, Firewall platforms, Security fundamentals
- SSL VPN
- Secure Sockets Layer VPNFortiOS 8.0 removed SSL VPN tunnel mode.On this site: Security fundamentals
- SSM
- Source Specific MulticastReceivers join a specific source and group; no RP needed.On this site: SD-Access campus fabric
- SSO
- Single Sign OnOne login across many tools, through an IdP.On this site: Cloud architecture
- SSO
- Stateful SwitchoverThe standby supervisor keeps state in sync and takes over without dropping links.On this site: Switching and campus LAN, Troubleshooting, Wireless and mobile
- STIG
- Security Technical Implementation GuideUS Defence Information Systems Agency hardening guides, used alongside CIS Benchmarks.
- STP
- Spanning Tree ProtocolIEEE 802.1D; blocks redundant links to stop layer 2 loops.On this site: Troubleshooting
- STR
- Simultaneous Transmit and ReceiveWi-Fi 7 multi link mode where a device sends on one band while it receives on another.On this site: Wireless and mobile
- STRAP
- Not Expanded in Public Sources: a UK Handling CaveatDo not speculate.
- STS
- Static Transfer SwitchSolid state switch between two live sources in milliseconds.On this site: Data centre facilities, Troubleshooting
- SU
- Scalable UnitNVIDIA reference architecture building block: a fixed set of GPU servers and network, repeated to scale.
- SuperNIC
- NVIDIA Product TermHigh speed NIC optimised for AI east west traffic.
- SVI
- Switched Virtual InterfaceA VLAN's routed interface on a layer 3 switch.On this site: VXLAN EVPN and ACI, Troubleshooting, VMware NSX
- SVL
- StackWise Virtual LinkLink joining two Catalyst 9000 switches in StackWise Virtual, the successor to VSS.
- SXP
- SGT Exchange ProtocolCarries IP to security group tag mappings to devices that cannot tag traffic inline.On this site: SD-Access campus fabric
- SYN
- SynchroniseThe first packet of a TCP connection; the server answers with SYN ACK.On this site: Load balancing
- SYN, ACK, FIN, RST
- Synchronise, Acknowledge, Finish, ResetTCP flags; a SYN with no SYN ACK back points at the path, a firewall or the server.
- SyOps
- Security Operating ProceduresThe security rules users and administrators must follow on a given system.
- SYSC
- Senior Management Arrangements, Systems and ControlsFCA Handbook sourcebook covering systems, controls and outsourcing.
T
- T0 / T1
- Tier-0 gateway / Tier-1 gatewayNSX north south router / tenant router; short names used in documents and diagrams.
- TAC
- Technical Assistance CentreCisco's support centre; open cases with full evidence attached.On this site: Data centre networks, Troubleshooting
- TACACS
- Terminal Access Controller Access Control SystemUsually TACACS+, the Cisco device AAA protocol on TCP 49.On this site: Networking fundamentals, Servers and virtualisation, Troubleshooting
- TACACS+
- Terminal Access Controller Access Control System PlusDevice admin AAA on TCP 49 with per command authorisation.On this site: Network automation, Networking fundamentals, Resilience, risk and cost
- TB / GB / MB
- Terabyte / Gigabyte / MegabyteCapacity units; unit cost is often quoted per usable TB.
- TC 9.9
- ASHRAE Technical Committee 9.9Publishes the thermal guidelines for data processing environments.
- TCAM
- Ternary Content Addressable MemoryHardware memory for ACLs, QoS and routes; it can run out.
- TCCF
- Tier Certification of Constructed FacilityUptime certification of the built facility.On this site: Data centre facilities
- TCDD
- Tier Certification of Design DocumentsUptime certification of the design.On this site: Data centre facilities
- TCN
- Topology Change NotificationSpanning tree message that makes switches flush MAC tables.On this site: Switching and campus LAN, Troubleshooting
- TCO
- Total Cost of OwnershipFull lifecycle cost including exit; the fair basis for comparing vendor options.On this site: Resilience, risk and cost
- TCOS
- Tier Certification of Operational SustainabilityUptime certification of how the site is run.On this site: Data centre facilities
- TCP
- Transmission Control ProtocolReliable transport with a three way handshake.On this site: Load balancing, Network automation, SD-Access campus fabric
- TCP/IP
- Transmission Control Protocol and Internet ProtocolThe internet protocol suite: IP for addressing and routing, TCP for reliable delivery.On this site: VMware NSX
- TCS
- Technology Cooling SystemThe liquid loop between the coolant distribution unit and the servers' cold plates.On this site: Data centre facilities
- TDA
- Technical Design AuthorityThe board that reviews and approves technical designs against agreed standards.
- TE
- Type EnforcementSidewinder's mandatory access control that compartments its OS.
- TEAP
- Tunnel EAPStandard EAP tunnel method that can check both machine and user in one session.On this site: Wireless and mobile, Security
- TEP
- Tunnel EndpointGeneve endpoint on hosts (vmk10, vmk11) and Edges; test with vmkping.On this site: VXLAN EVPN and ACI, Private cloud and storage, Troubleshooting
- TFTP
- Trivial File Transfer ProtocolSimple UDP 69 file transfer with no security; avoid on secure networks.On this site: Networking fundamentals
- TGT
- Ticket Granting TicketThe first Kerberos ticket, used to ask the KDC for tickets to services.On this site: Servers and virtualisation
- TIA
- Telecommunications Industry AssociationPublishes TIA-942, the data centre infrastructure standard.On this site: Data centre facilities
- TIA-568
- TIA-568 cabling StandardStructured cabling performance and wiring.On this site: Data centre facilities
- TIA-606
- TIA-606 labelling StandardAdministration and labelling of cabling and pathways.On this site: Data centre facilities
- TIA-942
- TIA-942 data Centre StandardTelecommunications infrastructure standard for data centres: spaces, cabling, ratings.On this site: Data centre facilities
- TIBER EU
- Threat Intelligence Based Ethical Red Teaming (EU)European red team framework aligned with DORA TLPT.
- TLOC
- Transport LocatorCatalyst SD-WAN identifier for an edge's WAN attachment.On this site: SD-WAN and SDN
- TLPT
- Threat Led Penetration TestingDORA advanced testing for significant firms, typically every three years.On this site: Resilience, risk and cost
- TLS
- Transport Layer SecurityEncrypts HTTPS, syslog over TLS and many management protocols.On this site: Network automation, SD-Access campus fabric, AWS, Azure and Google Cloud
- TLV
- Type, Length, ValueExtensible field format used by IS-IS and LLDP.
- TM Forum
- TeleManagement ForumTelco standards body (eTOM, SID, Open APIs)On this site: Network automation, Design authority, Wireless and mobile
- TN
- Transport NodeAn ESXi host or Edge prepared for NSX.
- TOGAF
- The Open Group Architecture FrameworkCommon enterprise architecture framework.On this site: Design authority
- ToR
- Top of RackLeaf switch in each rack; the usual spine and leaf position.On this site: Troubleshooting, VMware NSX
- ToR / EoR / MoR
- Top of Rack / End of Row / Middle of RowWhere access switches sit relative to servers.
- ToS
- Type of ServiceOriginal IPv4 header byte, now holding DSCP and ECN bits.
- TPID
- Tag Protocol Identifier0x8100 at the start of an 802.1Q tag.On this site: Networking fundamentals, Switching and campus LAN
- TPM
- Trusted Platform ModuleHardware root of trust for secure boot and attestation.On this site: IoT and edge
- TRM
- Tenant Routed MulticastMulticast routing inside EVPN VRFs.On this site: VXLAN EVPN and ACI
- TTL
- Time To LiveHop counter in the IP header.On this site: Load balancing, VXLAN EVPN and ACI, Data centre networks
- TZ
- Transport ZoneSets which nodes can see which segments: overlay or VLAN.
U
- UAT
- User Acceptance TestingFinal acceptance testing before a pod is handed over.
- UC
- Underpinning ContractContract with an external supplier that supports the SLA, such as vendor support.On this site: Support and service management
- UCS
- Unified Computing SystemCisco's server family.
- UCS
- User Configuration SetF5 BIG-IP archive of the full configuration, used for backup and restore.On this site: Load balancing
- UDLD
- Unidirectional Link DetectionFinds one way links; aggressive mode err disables the port.On this site: Switching and campus LAN, Troubleshooting
- UDP
- User Datagram ProtocolConnectionless transport for DNS, NTP, syslog, VXLAN and Geneve.On this site: Load balancing, Network automation, SD-Access campus fabric
- UEFI
- Unified Extensible Firmware InterfaceModern firmware that replaces BIOS, with Secure Boot and support for large disks.On this site: Servers and virtualisation
- UFM
- Unified Fabric ManagerNVIDIA management platform for InfiniBand fabrics.On this site: AI infrastructure
- UI
- User InterfaceThe screen or web console people use.On this site: Troubleshooting, VMware NSX
- UKSV
- United Kingdom Security VettingThe body that carries out national security vetting, including DV; target 95 days for DV.
- UNS
- Unified NamespaceOne structured MQTT topic tree where every system publishes its current state.On this site: IoT and edge, Operational technology
- UPF
- User Plane Function5G core function that forwards user data between the radio network and data networks.On this site: Wireless and mobile
- UPI
- Ultra Path InterconnectIntel's link between processor sockets in a server.On this site: Servers and virtualisation
- UPI
- User Provisioned InfrastructureOpenShift install on machines you prepare.On this site: Servers and virtualisation
- UPS
- Uninterruptible Power SupplyBattery backed power that bridges to generator start.On this site: AI infrastructure, Data centre facilities, Data centre networks
- URL
- Uniform Resource LocatorA web address, including API endpoints.On this site: Troubleshooting
- uRPF
- Unicast Reverse Path ForwardingAnti spoofing check on source addresses; strict or loose mode.On this site: Routing protocols, Security fundamentals, Troubleshooting
- USB
- Universal Serial BusStandard port for peripherals; often locked down on servers and OT kit to stop malware and data loss.On this site: Private cloud and storage, Troubleshooting
- USM
- User Based Security ModelSNMPv3 security with users, authentication and privacy.
- UTC
- Coordinated Universal TimeThe reference for NTP and PTP; MiFID II measures clock divergence from it.On this site: Cloud architecture, Design authority, Networking fundamentals
- UTD
- Unified Threat DefenseCisco Snort based intrusion prevention and URL filtering on routers.On this site: Troubleshooting
V
- VADP
- vSphere Storage APIs for Data ProtectionHow backup tools take VM level backups from vSphere.
- VCF
- VMware Cloud FoundationFull stack of vSphere, vSAN and NSX; VCF 9.0 released June 2025.On this site: Private cloud and storage, Servers and virtualisation, VMware NSX
- vCPU / pCPU
- Virtual CPU / Physical CPUThe vCPU to pCPU ratio is a key density and unit cost input.
- VCSA
- vCenter Server ApplianceThe vCenter VM that manages hosts and the VDS.
- VDC
- Virtual Device ContextSplits a Nexus 7000 into separate logical switches. Also Virtual Data Centre.On this site: Troubleshooting
- VDI
- Virtual Desktop InfrastructureDesktops hosted on central servers.
- VDOM
- Virtual DomainSplits one FortiGate into separate virtual firewalls.On this site: Troubleshooting
- VDS
- vSphere Distributed SwitchvCenter's distributed switch; the NSX host switch since NSX 4.0.On this site: Troubleshooting, VMware NSX
- VESDA
- Very Early Smoke Detection ApparatusAspirating smoke detection used in data halls.On this site: Data centre facilities
- vGPU
- Virtual GPUNVIDIA software that shares a GPU between VMs.
- VIB
- vSphere Installation BundleSoftware package on ESXi; NSX installs its kernel modules as VIBs.
- VIP
- Virtual IPShared address, such as the NSX Manager cluster VIP or a load balancer VIP.On this site: Load balancing, Firewall platforms, Troubleshooting
- VKS
- vSphere Kubernetes ServiceKubernetes clusters run on VCF.
- VLAN
- Virtual LANA separate broadcast domain on shared switches; IDs 1 to 4094.On this site: Government and defence, IoT and edge, IP addressing and subnetting
- VLSM
- Variable Length Subnet MaskingUsing different prefix lengths inside one address block.On this site: IP addressing and subnetting
- VM
- Virtual MachineA guest server on a hypervisor; attaches to NSX segments.On this site: AWS, Azure and Google Cloud, Design authority, Resilience, risk and cost
- VMFS
- Virtual Machine File SystemvSphere's clustered file system on block storage.On this site: Servers and virtualisation
- vmk
- VMkernel AdapterESXi host interface for management, vMotion, storage or NSX TEPs.On this site: Troubleshooting
- VMM
- Virtual Machine Manager (domain)ACI integration with vCenter or Kubernetes to learn endpoints and push networks.On this site: VXLAN EVPN and ACI, Troubleshooting
- vMotion
- VMware Live Migration (product feature)Moves running VMs between hosts; needs low latency layer 2 or routed vMotion networks.On this site: Private cloud and storage, Servers and virtualisation, Switching and campus LAN
- VMS
- Video Management SystemSoftware that manages cameras, recording and viewing.On this site: IoT and edge
- VMSA
- VMware Security AdvisoriesBroadcom's notices for VMware vulnerabilities and their fixes.On this site: VMware NSX
- vMSC
- vSphere Metro Storage ClusterStretched vSphere cluster over synchronous storage between two sites.
- VN
- Virtual NetworkIn SD-Access, a VRF that keeps groups of users and devices apart.On this site: SD-Access campus fabric, Troubleshooting
- VNI
- VXLAN Network Identifier24 bit segment ID; Geneve uses the same size VNI in NSX.On this site: VXLAN EVPN and ACI, Routing protocols, SD-WAN and SDN
- VNI / VNID
- VXLAN Network Identifier24 bit segment ID, about 16 million segments.
- vNIC
- Virtual Network Interface CardA VM's network card, where the DFW is enforced.On this site: Troubleshooting
- VoIP
- Voice over IPPhone calls carried as IP packets, which need low latency and jitter.On this site: Networking fundamentals, Servers and virtualisation, Switching and campus LAN
- vPC
- Virtual Port ChannelNexus feature: one bundle to two switches with separate control planes.On this site: Network automation, VXLAN EVPN and ACI, Data centre networks
- VPC
- Virtual Private CloudSelf service network construct in AWS and in recent NSX releases. Not the same as Nexus vPC.On this site: AWS, Azure and Google Cloud, Cloud architecture
- VPLS
- Virtual Private LAN ServiceMultipoint layer 2 VPN over MPLS.On this site: WAN, MPLS and VPN
- VPN
- Virtual Private NetworkPrivate connectivity over a shared or public network.On this site: SD-Access campus fabric, AWS, Azure and Google Cloud, Cloud architecture
- VPNv4
- VPN IPv4 address FamilyMP-BGP routes made of an RD plus an IPv4 prefix, carried between PEs.On this site: Troubleshooting
- VPNv4 / VPNv6
- VPN IPv4 / IPv6 address FamiliesMP-BGP families for L3VPN routes at the WAN edge.
- VRF
- Virtual Routing and ForwardingSeparate routing tables on one device; VRF Lite without MPLS.On this site: AI infrastructure, SD-Access campus fabric, Private cloud and storage
- VRLA
- Valve Regulated Lead AcidTraditional UPS battery type; lithium ion is the alternative.On this site: Data centre facilities
- VRRP
- Virtual Router Redundancy ProtocolOpen standard virtual gateway; preempts by default.On this site: Data centre networks, Networking fundamentals, Switching and campus LAN
- VSAN
- Virtual Storage Area NetworkCisco feature that splits FC fabrics into separate virtual SANs.On this site: Private cloud and storage
- vSAN
- VMware vSAN (virtual SAN)Software defined storage across ESXi hosts; part of VCF.On this site: VXLAN EVPN and ACI, Private cloud and storage, Servers and virtualisation
- VSC
- Virtualisation Service ClientHyper-V driver in a guest that talks to the host's VSP over VMBus.On this site: Servers and virtualisation
- VSID
- Virtual Subnet IdentifierThe 24 bit segment ID in NVGRE.
- VSL
- Virtual Switch LinkThe link joining two chassis in a VSS pair.On this site: Switching and campus LAN, Troubleshooting
- VSP
- Virtualisation Service ProviderHyper-V host component that serves synthetic devices to guests.On this site: Servers and virtualisation
- VSS
- Virtual Switching SystemTwo Catalyst 6500 or 6800 chassis acting as one. Also vSphere Standard Switch.On this site: Data centre networks, Support and service management, Switching and campus LAN
- VSS
- vSphere Standard SwitchPer host virtual switch. Not the same as Catalyst VSS.On this site: Data centre networks, Support and service management, Switching and campus LAN
- VTEP
- VXLAN Tunnel EndpointDevice or interface that adds and removes VXLAN headers.On this site: VXLAN EVPN and ACI, Data centre networks, IP addressing and subnetting
- VTI
- Virtual Tunnel InterfaceRoute based IPsec presented as an interface.On this site: WAN, MPLS and VPN
- VTP
- VLAN Trunking ProtocolShares VLANs between Cisco switches; transparent or version 3 is safer.On this site: Switching and campus LAN, Troubleshooting
- VTY
- Virtual TeletypeThe virtual terminal lines for SSH access; lock them down with an access class.
- VVF
- VMware vSphere FoundationSmaller Broadcom bundle; does not include NSX networking.
- vVols
- Virtual VolumesvSphere storage model with one array volume per VM disk.On this site: Private cloud and storage, Servers and virtualisation
- VXLAN
- Virtual Extensible LANLayer 2 over UDP 4789; 50 bytes overhead; used by NSX-V and Nexus fabrics.On this site: Network automation, SD-Access campus fabric, Design authority
W
- WAF
- Web Application FirewallProtects web applications from attacks such as injection.On this site: Load balancing, AWS, Azure and Google Cloud, Security fundamentals
- WAN
- Wide Area NetworkLinks that join sites over distance, such as MPLS, internet or SD-WAN.On this site: Load balancing, SD-Access campus fabric, AWS, Azure and Google Cloud
- WDM
- Wavelength Division MultiplexingCarrying several wavelengths on one fibre; CWDM and DWDM are types.
- WEEE
- Waste Electrical and Electronic Equipment (regulations)UK rules for disposing of retired IT equipment.On this site: Private cloud and storage
- WIPS
- Wireless Intrusion Prevention SystemDetects and contains rogue access points and wireless attacks.On this site: Wireless and mobile
- WLC
- Wireless LAN ControllerManages access points centrally: configuration, radio settings and roaming.On this site: Troubleshooting, Home lab
- WLD
- Workload DomainA VCF unit of compute, storage and network for tenant workloads.
- WMM
- Wi-Fi MultimediaWi-Fi quality of service with four queues: voice, video, best effort and background.On this site: Wireless and mobile, Troubleshooting
- WORM
- Write Once, Read ManyImmutable storage that cannot be changed until retention expires.
- WPA2
- Wi-Fi Protected Access 2Wi-Fi security with AES, in Personal (passphrase) and Enterprise (802.1X) modes.On this site: Wireless and mobile
- WPA3
- Wi-Fi Protected Access 3Current Wi-Fi security, with SAE for Personal and protected management frames as standard.On this site: IoT and edge, Wireless and mobile
- WRED
- Weighted Random Early DetectionDrops some packets early to avoid queue overflow, by class.On this site: Routing protocols, WAN, MPLS and VPN
- WSUS
- Windows Server Update ServicesMicrosoft server that downloads Windows updates and lets admins approve them for the network.On this site: Servers and virtualisation
- WUE
- Water Usage EffectivenessLitres of water per kWh of IT energy a data centre uses.On this site: Data centre facilities
- WWN
- World Wide NameUnique 64 bit identifier for a Fibre Channel device.
- WWN / WWPN
- World Wide Name / World Wide Port NameFibre Channel identities used in zoning.
- WWPN
- World Wide Port NameIdentifier for one FC port, used in zoning.On this site: Private cloud and storage
X
- X.509
- ITU Certificate StandardThe format of PKI certificates.On this site: IoT and edge
- XML
- Extensible Markup LanguageData format used by NETCONF.On this site: Network automation
Y
- YAML
- YAML Ain't Markup LanguageReadable data format used by Ansible playbooks.On this site: Network automation
- YANG
- Yet Another Next GenerationData modelling language for network configuration and telemetry.On this site: Support and service management
- YARN
- Yet Another Resource NegotiatorHadoop's resource scheduler for big data pods.
Z
- ZBFW
- Zone Based Policy FirewallCisco IOS router firewall built on zones and zone pairs.On this site: Troubleshooting
- ZDA
- Zone Distribution AreaOptional TIA-942 point between the horizontal and equipment areas that makes recabling easier.On this site: Data centre facilities
- ZR
- Coherent Long Reach Optic Class (80 km and beyond)Used for metro DCI over DWDM.
- ZTNA
- Zero Trust Network AccessAccess granted per application after checking user and device.On this site: Security, WAN, MPLS and VPN
- ZTP
- Zero Touch ProvisioningDevices fetch their configuration automatically on first boot.On this site: Network automation, Data centre facilities, Data centre networks
Same letters
Same letters, different meaning
Some acronyms mean different things to different teams. A network engineer and a service manager can use the same two letters and talk past each other. I check the context before I expand one, and I spell it out in writing the first time.
Swipe sideways to see the whole diagram.
DR: designated router. OSPF elects one router on a shared segment to collect and pass on link state updates. Or disaster recovery. Getting a service back at a second site after a major failure.
AD: administrative distance. How much a router trusts a route source. Lower wins: connected 0, static 1, OSPF 110. Or Active Directory. The Microsoft directory for users, computers, groups and logins.
CE: customer edge. The customer router that peers with the provider edge in an MPLS VPN. Or Cyber Essentials. The UK government backed baseline security certification.
RT: route target. A BGP tag that decides which VRFs import a route in MPLS VPN or EVPN. Or route type. The kind of EVPN message, such as type 2 for MAC and IP, type 5 for prefixes.
| Letters | One meaning | Another meaning |
|---|---|---|
| AD | Administrative Distance (Cisco route source trust) | Active Directory (Microsoft directory behind ISE and AAA) |
| AF | Assured Forwarding (DSCP QoS classes) | Address Family (BGP: IPv4 unicast, VPNv4, L2VPN EVPN) |
| CA | Certificate Authority (issues certificates in a PKI) | Change authority (ITIL 4: whoever authorises a change; the CAB advises it) |
| CE | Customer Edge router (MPLS VPN) | Cyber Essentials (UK baseline security scheme) |
| CI | Configuration Item (CMDB record) | Continuous Integration (software build pipelines) |
| CSI | Continual Service Improvement (ITIL) | Container Storage Interface (Kubernetes storage plug ins, seen with Tanzu) |
| DR | Designated Router (OSPF) | Distributed Router (NSX), and also Disaster Recovery |
| DV | Developed Vetting (UK clearance) | Distance Vector (routing protocol family, such as RIP) |
| ESG | Edge Services Gateway (NSX-V) | Environmental, Social and Governance (corporate reporting) |
| MAC | Media Access Control address | Mandatory Access Control (Sidewinder type enforcement), and Message Authentication Code in cryptography |
| PDU | Protocol Data Unit (frame, packet, segment) | Power Distribution Unit (rack power strip) |
| RFC | Request for Comments (IETF standard) | Request for Change (ITIL) |
| RP | Root Port (spanning tree) | Rendezvous Point (PIM multicast) |
| RR | Route Reflector (iBGP) | Round Robin (load sharing method) |
| SA | Security Association (IPsec) | Solutions Architect (as in AWS SAP) |
| SPF | Shortest Path First (OSPF and IS-IS) | Security Policy Framework (HMG), and Sender Policy Framework (email DNS record) |
| SR | Service Router (NSX, runs on the Edge) | Segment Routing (source routing with MPLS labels or IPv6) |
| TEP | Tunnel Endpoint (NSX Geneve, on hosts and Edges) | VTEP is the VXLAN version on Nexus and ACI; RTEP is the NSX Federation remote TEP |
| VDC | Virtual Device Context (Nexus 7000) | Virtual Data Centre (cloud and VMware Cloud Director tenancy) |
| vPC / VPC | virtual Port Channel (Cisco Nexus) | Virtual Private Cloud (AWS, and recent NSX releases) |
| VSS | Virtual Switching System (Catalyst 6500 and 6800) | vSphere Standard Switch (per host virtual switch) |
| DC | Data Centre | Direct Current (power) |
| DORA | Digital Operational Resilience Act (EU regulation) | Discover, Offer, Request, Acknowledge (DHCP exchange) |
| ESA | Express Storage Architecture (vSAN) | European Supervisory Authorities (EBA, EIOPA, ESMA under DORA) |
| KVM | Kernel based Virtual Machine (hypervisor) | Keyboard, Video, Mouse (console switch) |
| OCP | OpenShift Container Platform (Red Hat) | Open Compute Project (open hardware) |
| PBR | Policy Based Redirect (ACI service insertion) | Policy Based Routing (routing by policy) |
| RAID | Redundant Array of Independent Disks (storage) | Risks, Assumptions, Issues and Dependencies (programme log) |
| RT | Route Target (BGP import and export policy) | Route Type (EVPN, as in RT 2 or RT 5) |
| XDR | InfiniBand 800 Gb/s generation | Extended Detection and Response (security tooling) |
Coverage
Built from every page on this site
This glossary is not written once and left. It is rebuilt from the pages themselves: every time a page spells out an acronym, the term and a link to that page are picked up here, alongside a curated list of wider industry terms.
30 pages linked
862 entries link straight to the page and section where I explain them. The rest are wider industry terms that no page covers yet.
Spotted a term that is missing or unclear? The full explanations live on the topic pages, starting with networking fundamentals.
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More areas I design and deliver
Every page follows the same idea: how it works, the choices that matter, and where I have used it. The foundations pages explain the basics the others build on.