Cisco Cisco IOS Software Release 12.0(22)S

BGP—Border Gateway Protocol. An interdomain routing protocol that replaces Exterior Border 
Gateway Protocol (EGP). BGP exchanges reachability information with other BGP systems. It is 
defined by RFC 1163.

Border Gateway Protocol—See BGP.

BGP/MPLS/VPN—A VPN solution that uses MPLS and BGP protocol to allow multiple remote 
customer sites to be connected over an IP backbone. Refer to RFC 2547 for details.

CE router—A customer edge router. A router that is part of a customer network and interfaces to a PE 
router.

customer network—A network that is under the control of an end customer. A customer network can 
use private addresses as defined in RFC 1918. Customer networks are logically isolated from each other 
and from the provider network. A customer network is also known as a C network.

egress PE—The provider edge router through which traffic moves from the backbone to the destination 
VPN site.

flow—A set of packets with the same source IP address, destination IP address, source/destination 
ports, and type-of-service, and the same interface on which flow is monitored. Ingress flows are 
associated with the input interface, and egress flows are associated with the output interface.

ingress PE—The provider edge router through which traffic enters the backbone (provider network) 
from a VPN site.

label—A short, fixed length identifier that tells switching nodes how the data (packets or cells) should 
be forwarded.

MPLS—Multiprotocol label switching. An emerging industry standard on which label switching is 
based.

multiprotocol label switching—See MPLS.

open shortest path first—See OSPF.

OSPF—Open Shortest Path First. A link-state, hierarchical Interior Gateway Protocol (IGP) routing 
algorithm proposed as a successor to RIP in the Internet community. OSPF features include least-cost 
routing, multipath routing, and load balancing.

PE router—A provider edge router. A router at the edge of a provider network that interfaces to CE 
routers.

provider network—A backbone network that is under the control of a service provider and provides 
transport among customer sites. A provider network is also known as the P network.

virtual private network—See VPN.

VPN—Virtual private network. A network that enables IP traffic to use tunneling to travel securely over 
a public TCP/IP network.

VRF—VPN routing and forwarding instance. The VRF is a key element in the MPLS VPN technology. 
VRFs exist on PEs only. A VRF is populated with VPN routes and allows multiple routing tables in a 
PE. One VRF is required per VPN on each PE in the VPN.