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Question about BGP "remove-private-as"

In Cisco document about BGP "remove-private-as", it says "if the ASpath contains the AS of the peering router (through eBGP), then the AS's will not be stripped".

My question is: when a route is received from the peering router, its AS Path always has the peering router's AS# appended. So the assumption in the document is always true. Then what's the point to even have the assumption?

PLease let me know if I'm incorrect somewhere.

Thanks

Gary

1 REPLY
Purple

Re: Question about BGP "remove-private-as"

Gary,

Consider this: A -- B -- C

If A has a private AS, all routes it advertises to B will contain that private AS#. If you have configured "remove-private-as" on B, it will strip that private AS# when advertising those routes to C. Now, if B somehow decides to advertise those routes back to A, that's where that statement from the Cisco Document comes in. If B stripped that private AS# from these routes, A will not know that it should drop those routes because it contains its own AS#. That's the kind of situation it is protecting against.

Hope that helps - pls do rate the post if it does

Paresh

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