[c-nsp] as-path access lists

[Justin M. Streiner]

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