vapor corrosion inhibitor

See VCI.

variable bit rate

See VBR.


Variable bit rate. For ATM1 and ATM2 intelligent queuing (IQ) interfaces, data that is serviced at a varied rate within defined limits. VBR traffic adds the ability to statistically oversubscribe user traffic.


Virtual circuit. A software-defined logical connection between two network devices that is not a dedicated connection but acts as though it is. It can be either permanent (PVC) or switched (SVC). VCs are used in ATM, Frame Relay, and X.25. See also VPI, VCI, PVC, and SVC.


  1. Vapor corrosion inhibitor. Small cylinder packed with the router that prevents corrosion of the chassis and components during shipment.


  1. Virtual circuit identifier. A 16-bit field in the header of an ATM cell that indicates the particular virtual circuit the cell takes through a virtual path. Also called a logical interface. See also VPI.


virtual channel

Enables queuing, packet scheduling, and accounting rules to be applied to one or more logical interfaces. See also virtual channel group.

virtual channel group

Combines virtual channels into a group and then applies the group to one or more logical interfaces. See also virtual channel.

virtual circuit

Represents a logical connection between two Layer 2 devices in a network.

virtual circuit identifier

See VCI.

virtual connection

See VC.

virtual LAN (VLAN)-tagged frame

Tagged frame whose tag header carries both VLAN identification and priority information.

virtual link

In OSPF, a link created between two routers that are part of the backbone but are not physically contiguous.

virtual local area network


virtual path

Combination of multiple virtual circuits between two devices in an ATM network.

virtual path identifier

See VPI.

virtual private network

See VPN.

Virtual Router Redundancy Protocol



Virtual local area network. A logical group of network devices that appear to be on the same LAN, regardless of their physical location. VLANs are configured with management software, and are extremely flexible because they are based on logical, rather than physical, connections.


Virtual path identifier. An 8-bit field in the header of an ATM cell that indicates the virtual path the cell takes. See also VCI.


Virtual private LAN service. An Ethernet-based multipoint-to-multipoint Layer 2 VPN service used for interconnecting multiple Ethernet LANs across an MPLS backbone. VPLS is specified in the IETF draft, Virtual Private LAN Service.


Virtual private network. A private data network that uses a public TCP/IP network, typically the Internet, while maintaining privacy with a tunneling protocol, encryption, and security procedures. See also tunneling protocol.

VRF instance

VPN routing and forwarding instance. A VRF instance for a Layer 3 VPN implementation that consists of one or more routing tables, a derived forwarding table, a set of interfaces that use the forwarding table, and a set of policies and routing protocols that determine what goes into the forwarding table.

VRF table

Routing instance table that stores VRF routing information. See also VRF instance.


Virtual Router Redundancy Protocol. On Fast Ethernet and Gigabit Ethernet interfaces, allows you to configure virtual default routers.