Glossary
GL-11
Cisco 10000 Series Router Software Configuration Guide
OL-2226-23
VC
Virtual Circuit. Also referred to as Virtual Channel. Used in ATM applications. A link that seems and
behaves like a dedicated point-to-point line or a system that delivers packets in sequence, as happens
on an actual point-to-point network. In reality, the data is delivered across a network via the most
appropriate route. The sending and receiving devices do not have to be aware of the options and the
route is chosen only when a message is sent. There is no pre-arrangement, so each virtual circuit exists
only for the duration of that one transmission.
VCI
Virtual channel identifier. A 16-bit field in the header of an ATM cell. The VCI, together with the VPI,
is used to identify the next destination of a cell as it passes through a series of ATM switches on its way
to its destination. ATM switches use the VPI/VCI fields to identify the next network VCL that a cell
needs to transmit on its way to its final destination. The function of the VCI is similar to that of the
DLCI in Frame Relay.
VLAN
Virtual LAN. Group of devices on one or more LANs that are configured (using management software)
so that they can communicate as if they were attached to the same wire, when in fact they are located
on a number of different LAN segments. Because VLANs are based on logical instead of physical
connections, they are extremely flexible.
VPDN
Virtual Private Dialup Network. A system that permits dial-in networks to exist remotely to home
networks, while giving the appearance of being directly connected. VPDNs use L2TP and L2F to
terminate the Layer 2 and higher parts of the network connection at the home gateway.
VPI
Virtual path identifier. An 8-bit field in the header of an ATM cell. The VPI, together with the VCI, is
used to identify the next destination of a cell as it passes through a series of ATM switches on its way
to its destination. ATM switches use the VPI/VCI fields to identify the next VCL that a cell needs to
transmit on its way to its final destination. The function of the VPI is similar to that of the DLCI in
Frame Relay.
VPN
Virtual private network. A secure IP-based network that shares resources on one or more physical
networks. A VPN contains geographically dispersed sites that can communicate securely over a shared
backbone. VPNs enable IP traffic to travel securely over a public TCP/IP network by encrypting all
traffic from one network to another. A VPN uses “tunneling” to encrypt all information at the IP level.
vpnv4
Used as a keyword in commands to indicate VPN-IPv4 prefixes. These prefixes are customer VPN
addresses, each of which has been made unique by the addition of an 8-byte route distinguisher.
VRF
Virtual routing and forwarding instance. A VRF consists of an IP routing table, a derived forwarding
table, a set of interfaces that use the forwarding table, and a set of rules and routing protocols that
determine what goes into the forwarding table. In general, a VRF includes the routing information that
defines a customer VPN site that is attached to a PE router.
VSA
Vendor-Specific Attribute. An attribute that has been implemented by a particular vendor. It uses the
attribute Vendor-Specific to encapsulate the resulting AV pair: essentially, Vendor-Specific =
protocol:attribute = value.
W
WAN
Wide area network. A data communications network that spans any distance and is usually provided by
a public carrier (such as a telephone company or service provider).
