The Border Gateway Protocol (BGP), defined in RFC 1771, provides loop-free interdomain routing between autonomous systems. (An autonomous system [AS] is a set of routers that operate under the same administration.) BGP is often run among the networks of Internet service providers (ISPs).
Enter the global configuration mode and issue the following commands to enable BGP routing and establish a BGP routing process:
||Enables the BGP routing process, which places the router in router configuration mode|
||Flags a network as local to this autonomous system and enters it to the BGP table|
BGP supports two kinds of neighbors: internal and external. Internal neighbors are in the same autonomous system; external neighbors are in different autonomous systems. Normally, external neighbors are adjacent to each other and share a subnet, while internal neighbors may be anywhere in the same autonomous system.
To configure BGP neighbors, issue the following command in router configuration mode:
||Specifies a BGP neighbor|
The following example shows how BGP neighbors on an autonomous system are configured to share information.
router bgp 109
neighbor 126.96.36.199 remote-as 167
neighbor 188.8.131.52 remote-as 109
neighbor 184.108.40.206 remote-as 99
In the example, a BGP router is assigned to autonomous system 109, and
two networks are listed as originating in the autonomous system. Then
the addresses of three remote routers (and their autonomous systems) are
listed. The router being configured will share information about networks
220.127.116.11 and 18.104.22.168 with the neighboring routers. The first router
listed is in a different autonomous system; the second neighbor's
router configuration command specifies an internal neighbor (with the
same autonomous system number) at address 22.214.171.124 and the
third neighbor's r
emote-as router configuration command specifies
a neighbor on a different autonomous system.
If you have configured BGP on your network, and want Netflow to report on autonomous systems (AS info), issue the following command on the router in global configuration mode:
||Exports the Netflow cache entries to the specified IP address. Use the IP address of the NetFlow Analyzer server and the configured Netflow listener port. The default port is 9996.|
||Exports NetFlow cache entries in the specified version format (5 or 7). If your router uses BGP, you can specify that either the origin or peer ASs are included in exports – it is not possible to include both.|