BGP regexp

[stephen.stack]

What does this as-path list do, if appliead to a routemap outbound?

ip as-path access-list 70 permit ^$

ip as-path access-list 70 permit ^1234$

Thanks

Stephen

[Jon Marshall · Accepted solution]

Stephen

Permits any routes with no AS ie. they originated in the local AS or an AS of 1234.

Jon

[stephen.stack]

ah yes... makes perfect sense, and has the desired effect.

Thanks Jon,

Stephen

[Harold Ritter]

Stephen,

It allows paths with an empty AS PATH (locally originated prefixes) or paths that have been originated by and received from AS 1234.

Regards

[marikakis]

Hello,

The entry that references ^1234$ allows all routes originated in neighboring AS 1234 only if the neighboring AS 1234 does not make use of prepend. If neighboring AS 1234 prepends its own AS one or more times, updates will not pass. ^1234$ means "only a single 1234 in AS path and nothing else". You need something like ^(1234_)+$ to allow all updates from neighboring AS 1234 under any circumstances.

Kind Regards,

M.