[nsp] regexp help!!

[Nick Kraal]

I am having slight trouble with some regular expresions to filter as_path
announcements to a transit customer.

AS1++++AS2-----AS3++++AS5
                   +           |
                   +           |
                 AS4 -----

+++ Transit link
----  Peering link

AS2 is providing transit services to AS1. AS4 is providing transit services
to AS2. The link between AS2 and AS3 is a peering link. How does AS2
announce/filter annoucements to AS1 to only allow entries to AS3 (and to
customers like AS5) via AS4 and none via the peering link. AS4 announces all
AS3 and their customers (eg. AS5) prefixes to AS2.

We have made the following route-map at AS2:
---------------------------
route-map AS1-FILTER-OUT deny 10
 match as-path 1
!
route-map AS1-FILTER-OUT permit 20
!
ip as-path access-list 1 permit ^1$
----------------------------
and from:
    sh ip bgp neighbors <AS1 BGP peer IP address> advertised-routes |
include 3

This shows the following
AS3_AS5
AS4_AS3_AS5

What I am trying to achieve on BGP announcements from AS2 to AS1 is AS3
annoucement reachability:
AS4_AS3
AS4_AS3_AS5

------------------------
Many thanks in advance.

-nick/