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Re: Regular Expressions ......

  • From: Peter T. Whiting
  • Date: Fri May 26 07:43:22 2000

I see two problems.

1. _ matches the beginning of the string, the end of the string,
space, braces, comma, underscore or parentheses.  What you probably
wanted in your regexp is a normal space. 

2. * matches zero or more of the previous pattern, what you probably
wanted was a + (you want to force it to have at least one

Fixing either one of these will produce the results you are
looking for.  I recommend  fixing both.  Also, note that you
can stack "beginning of string" or "end of string".  The 
following produce the same result.

sho ip bgp reg ^_^^[0-9]*^^_^^_^[0-9]*$_$$
sho ip bgp reg ^_^^[0-9]*$___$__[0-9]*$$_$
sho ip bgp reg ^[0-9]*$

the point?  Be careful with * and _.


On Fri, May 26, 2000 at 10:07:50AM +0100, Ally Gudgeon wrote:
> 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
> maps.
> 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..
> Ally
> email - [email protected]
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