Information Technology Reference
In-Depth Information
BGP Neighbors
Figure 9-1
Service Provider 1
AS 100
Service Provider 3
AS 300
Service Provider 2
AS 400
Router A
1.1.1.1
1.1.1.2
Router B
Enterprise
Autonomous System
AS 200
Before routing updates can be exchanged between two BGP routers, the routers must become
established neighbors. After BGP routers establish a TCP connection, exchange information,
and accept the information, they become established neighbors and start exchanging routing
updates. If the neighbors do not reach an established state, BGP updates are not exchanged. The
information exchanged before the neighbors are established includes the following: BGP
version number, AS number, and the BGP router ID (RID).
The configuration to establish BGP neighbors between Router A and Router B in Figure 9-1 is
as follows:
The Router A configuration that establishes BGP neighbors between Router A and
Router B is
router bgp 100
neighbor 1.1.1.2 remote-as 200
The Router B configuration that establishes BGP neighbors between Router A and
Router B is
router bgp 200
neighbor 1.1.1.1 remote-as 100
To verify BGP neighbors, use the
command, as shown in Example 9-1.
The external BGP neighbor is 1.1.1.2 with a remote AS of 200. The BGP state is established.
The router ID of the neighbor is 10.10.10.10. The external port is 179, the TCP port for BGP.
The keepalive is 60 seconds and the holdtime is 180 seconds.
show ip bgp neighbors
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