North American Network Operators Group

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Regular Expressions ......

  • From: Ally Gudgeon
  • Date: Fri May 26 05:18:36 2000

Hi All,

I am having a few problems getting my BGP filtering to work - and am
experiencing some strange results..

I have two routers connected to a peering point, we have decided that we
want to set local preferences of

110 to 1-deep AS-paths (as-path ACL 1)
100 to 2-deep AS-paths (as-path ACL 2)
and 90 to 3-deep AS-paths (as-path ACL 3)
and to not accept 4-deep AS-paths (as-path ACL 4)

I have the following as-path ACLs to try to set that and am using route

ip as-path access-list 1 permit ^[0-9]*$
ip as-path access-list 2 permit ^[0-9]*_[0-9]*$
ip as-path access-list 3 permit ^[0-9]*_[0-9]*_[0-9]*$
ip as-path access-list 4 permit .*

This appears to have failed miserably....It is not setting local prefs
correctly if they are 3-deep and have a repetition of an AS number it sees
it as 4-deep
If they are 4 AS's deep it doesn't apply a local preference but if it knows
it from our other core router it sets a local pref of 100 but prefers the
direct route?

(ALSO: If I do a sh ip bgp reg ^[0-9]*_[0-9]*$ it lists both 1-deep and
2-deep AS's....surely it should just list 2-deep?)

Any help would be greatly appreciated!......

Thanks in advance..


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