[c-nsp] as-path access lists

[Michael Smith]

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> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-
> bounces at puck.nether.net] On Behalf Of Justin M. Streiner
> Sent: Wednesday, November 17, 2004 8:17 AM
> To: Alex Foster
> Cc: cisco-nsp at puck.nether.net
> Subject: RE: [c-nsp] as-path access lists
> 
> On Wed, 17 Nov 2004, Alex Foster wrote:
> 
> > Essentially, I want to receive more routes than I am at the
> > moment - unfortunately the 3550 I am using to connect to Level3
> > will only support 16000 prefixes - and I cant therefore receive
> > all routes - hence the as-path
> > Filter - but this is restricting it too much.  Is there any way
> > to receive partial routes - and then to be selective about them -
> > ie: I really don't want to receive more than +7000 this should be
> > enough for me to perform the Load Balancing I am looking for.
> 
> Probably the best way would be to check if Level3 will tag customer
> routes with a community, as another poster mentioned.  Then you can
> filter on that community as well.  Otherwise, you're likely going
> to have to go through the process of picking other AS path regex
> combinations to match against to get the additional routes you're
> looking for.
> 
> If you had to do it, some possible examples would be:
> ^(_3356)+$
> Matches all prefixes that have only 3356 in the AS path, regardless
> of how many times it's prepended, up to the maximum size of the AS
> path.
> 
> ^(_3356)+(_some other large backbone AS)+$
> Same thing, but with some other large AS as the origin; both
> elements may be prepended as many times as will fit in the AS_PATH
> data space itself.  
> 
> jms

You could also do a loose "add one more AS to the path" and see what
that gets you.

ip as-path access-list 10 permit ^(_3356_)+([0-9]+_)$

Mike

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