Purpose

For BGP to run on a router in your network, you must define the local autonomous system (AS) number, configure at least one group, and include information about at least one peer in the group. If the peer is an EBGP peer, include the peer’s AS number. For all peers, include either the peer’s interface IP address or loopback (lo0) IP address. When configuring BGP on an interface, you must also include the family inet statement at the [edit interfaces interface-name unit logical-unit-number] hierarchy level.

Figure 1 illustrates the example configurations used in this topic.

Figure 1: BGP Configuration Topology

The network in Figure 1 consists of two directly connected ASs. IP addresses included in the network diagram are as follows:

• 10.1.12.1—AS 650001external IP address on R1
• 10.1.45.2—AS 650001 external IP address on R5
• 10.0.0.1—Internal loopback (lo0) IP address for R1
• 10.0.0.5—Internal loopback (lo0) IP address for R5
• 10.1.12.2—AS 65002 external IP address on R2
• 10.1.45.1—AS 65002 external IP address on R5
• 10.0.0.2—Internal loopback (lo0) address for R2
• 10.0.0.3—Internal loopback (lo0) address for R3
• 10.0.0.4—Internal loopback (lo0) address for R4
• 10.0.0.6—Internal loopback (lo0) address for R6

All routers within each AS maintain an IBGP session between each router in that AS. R1 and R5 have an IBGP session through their loopback (lo0) interfaces: 10.0.0.1 and 10.0.05. R2, R3, R4, and R6 maintain IBGP sessions between each other through their loopback (lo0) interfaces: 10.0.0.2, 10.0.0.3, 10.0.0.4, and 10.0.0.6.

The two routers in AS 65001 each contain one EBGP link to AS 65002 (R2 and R4) over which they announce aggregated prefixes: 100.100/16. Routers at the edge of a network that communicate directly with routers in other networks are called border routers. Border routers use EBGP to exchange routing information between networks.

Adjacent BGP routers are referred to as neighbors or peers. Peers can be internal or external to the AS. Internal and external peers are configured slightly differently. In general, internal peers communicate using the loopback (lo0) interface, and external peers communicate through the shared interface. See Figure 1 for the loopback (lo0) and interface information.