BGP Notes – Confederations
- RFC 3065
- BGP confederations reduce the size of full mesh iBGP ASes by dividing it up into different areas.
- Confederations also remove the need for BGP synchronization since all iBGP routers will have all routes.
- In effect, your iBGP AS gets chopped up into different sub-ASes.
- Each router is a member of a sub-AS and is a neighbor with every other router in that sub-AS (full mesh).
- Neighbors within a sub-AS are called confederation iBGP neighbors.
- Confederation iBGP neighbors act just like any other iBGP neighbor.
- At least one member of each sub-AS is neighbored with members of different sub-ASes.
- Neighbors in different sub-ASes are called confederation eBGP neighbors.
- Confederation eBGP neighbors have a default TTL of 1 just like true eBGP neighbors.
- The NEXT_HOP PA is not changed when passing routes between sub-ASes.
- LOCAL_PREF is also preserved.
- Confederations use the AS_CONFED_SEQ and AS_CONFED_SET fields in the AS_PATH PA.
- These fields act like AS_PATHs to prevent loops.
- These fields are cleared out when the route is passed to an eBGP neighbor.
- If components of a summary route (an aggregate-address) have different AS_CONFED_SEQ values, the AS_CONFED_SET is used.
- Confederations ASes are not included when the router decides which route is best.
- BGP confederation routers are configured to be in a private ASN.
- The confederations should be private to avoid AS conflicts.
- The confederation identifier defines the AS at it appears to the world.
router bgp 65001 no synchronization bgp confederation identifier 123 bgp confederation peers 65002 65003 neighbor 126.96.36.199 remote-as 65002 neighbor 188.8.131.52 remote-as 65003
Comment with corrections, please.
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