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V

vapor corrosion inhibitor — See VCI.

variable bit rate — See VBR.

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.

VC — 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, SVC.

VCI — VCI can be either of the following:

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

Video on demand — See VOD.

Video services router — See VSR.

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 switch — A routing instance that can contain one or more bridge domains.

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 — See VLAN.

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 — See VRRP.

virtual loopback tunnel interface — See VT.

VLAN — 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.

VLANs span one or more ports on multiple devices. By default, each VLAN maintains its own Layer 2 forwarding database containing MAC addresses learned from packets received on ports belonging to the VLAN. See also bridge domain.

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

VOD — Video on demand. A unicast streaming video offering by service providers that enables the reception of an isolated video session per user with rewind, pause, and similar VCR-like capabilities.

VPI — 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.

VPLS — 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.

VPN — 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 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.

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

VSR — Video services router. A router used in a video services network to rout video streams between an access network and a metro or core network. The VSR is any M-series or MX-series router that supports the video routing package provided with JUNOS software Release 8.3 or later.

VT — Virtual loopback tunnel interface. VT interface that loops packets back to the Packet Forwarding Engine for further processing, such as looking up a route in a VRF routing table or looking up an Ethernet MAC address. A virtual loopback tunnel interface can be associated with a variety of MPLS and VPN-related applications, including VRF routing instances, VPLS routing instances, and point-to-multipoint LSPs.

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