3.7.e [ii] Confederations
The implementation of BGP confederation reduces the iBGP mesh inside an AS. The key is to divide an AS into multiple ASs and assign the whole group to a single confederation. Each AS alone has iBGP fully meshed and has connections to other ASs inside the confederation. Even though these ASs have eBGP peers to ASs within the confederation , the ASs exchange routing as if they used iBGP. In this way, the confederation preserves next hop, metric, and local preference information. To the outside world, the confederation appears to be a single AS. In order to configure a BGP confederation, issue this command:
bgp confederation identifier autonomous-system
The confederation identifier is the AS number of the confederation group. The issue of this command performs peering between multiple ASs within the confederation:
bgp confederation peers autonomous-system [autonomous-system]
Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 4032-4034). . Kindle Edition.