Consider a common problem [An Ink Drawing] Tier1-B sets local-preference for its customer to 120 and for its peer to 100.
How does Customer cause Tier1-B to prefer the path: Content -> Tier1-B -> Tier1-A -> Regular-Provider -> Customer instead of its default path: Content -> Tier1-B -> Backup-Provider -> Customer ? Solution 1 -------------- Customer advertises split prefixes to Regular-Provider. Eg., 10.0.2.0/24 and 10.0.3/24 rather than 10.0.2/23. This works, but causes bigger FIBs for everybody. Solution 2 -------------- Customer advertises its routes with communities published by Tier1-B to lower its local-preference to Backup-Provider. This requires Backup-Provider to pass communities through and for Customer to know what Backup-Provider's upstreams are. It is operationally cumbersome. Solution 3 -------------- Tier1-B implements a route-policy like: if as-path length ge 15 then set local-preference 80 endif Then Customer can add lots of AS prepends that will actually work!! Regards, Jakob.
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