BGP Confederations: An Alternative to Full Mesh Internal BGP (IBGP)
iBGP requires a full mesh between all BGP-speaking routers; route reflectors modify iBGP split-horizon rules, and BGP confederations modify iBGP AS-path processing
The full-mesh requirement is relaxed thourgh introduction of member autonomous systems into which the original autonomous system is split.
The addition autonomous system numbers are hidden from the outside world by modified AS-path update procedures.
The intraconfederation segment is removed from the AS path by the egress confederation router prior to prepending the official AS number when sending a BGP update to an external AS.
Intraconfederation eBGP sessions act like eBGP sessions from a session.establishment perspective, and they act like iBGP sessions from the BGP attribute-propagation perspective.
Output after BGP is configured:
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