system—A collection of networks that share the same routing protocol and that are under the same system administration.
ASBR—autonomous system border router. A device that connects and exchanges information between two or more autonomous systems.
BGP—Border Gateway Protocol. The exterior border gateway protocol used to exchange routing information between devices in separate autonomous systems. BGP uses Transmission Control Protocol (TCP). Because TCP is a reliable protocol, BGP does not experience problems with dropped or fragmented data packets.
device—customer edge device. The customer device that connects to the provider edge (PE) device.
EBGP—External Border Gateway Protocol. A BGP session between devices in different autonomous systems. When a pair of devices in different autonomous systems are more than one IP hop away from each other, an EBGP session between those two devices is called multihop EBGP.
IBGP—Internal Border Gateway Protocol. A BGP session between devices within the same autonomous system.
IGP—Interior Gateway Protocol. Internet protocol used to exchange routing information within an autonomous system. Examples of common Internet IGPs include Internal Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF), and Routing Information Protocol (RIP).
LDP—Label Distribution Protocol. A standard protocol between MPLS-enabled devices to negotiate the labels (addresses) used to forward packets. The Cisco proprietary version of this protocol is the Tag Distribution Protocol (TDP).
LER—label edge router. The edge device that performs label imposition and disposition.
LSR—label switch router. The role of an LSR is to forward packets in an MPLS network by looking only at the fixed-length label.
MPLS—Multiprotocol Label Switching. A switching method that forwards IP traffic using a label. This label instructs the devices and the switches in the network where to forward the packets based on preestablished IP routing information.
NLRI—Network Layer Reachability Information. BGP sends routing update messages containing NLRI, which describes the route. In this context, an NLRI is a prefix. A BGP update message carries one or more NLRI prefixes and the attributes of a route for the NLRI prefixes. The route attributes include a BGP next-hop gateway address, community values, and other information.
device—provider device. The core device in the service provider network that connects to provider edge (PE) devices. In a packet-switched star topology, a device that is part of the backbone and that serves as the single pipe through which all traffic from peripheral networks must pass on its way to other peripheral networks.
device—provider edge device. The label edge router (LER) in the service provider network that connects to the customer edge (CE) device.
RD—route distinguisher. An 8-byte value that is concatenated with an IPv4 prefix to create a unique VPN IPv4 (VPNv4) prefix.
RR—route reflector. A device that advertises, or reflects, IBGP learned routes to other IBGP peers without requiring a full network mesh.
RT—route target. Extended community attribute used to identify the VRF routing table into which a prefix is to be imported.
VPN—Virtual Private Network. A group of sites that, as a result of a set of administrative policies, can communicate with each other over a shared backbone.
prefix—IPv4 prefix preceded by an 8-byte route distinguisher. The VPN addresses are made unique by adding a route distinguisher to the front of the address.
VRF—VPN 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 provider edge (PE) device.