[c-nsp] Inbound traffic

Jon Lewis jlewis at lewis.org
Wed Feb 10 00:53:19 EST 2010

On Wed, 10 Feb 2010, Sherwin Torres wrote:

> Anyway, I agree but you might confuse on my inquiry. In the internet 
> cloud, there are lots of interconnected AS and if I'm going to prepend 
> the announcement to AS200 and AS300 - all inbound traffic will pass to 
> AS20 alone.

No necessarily.  Based on the info you provided, prepending once to 200 
and 300 will give you equal path lengths on the 3 paths, and something 
other than as-path will be used for best path selection.

x> Actually, what I want is - to isolate specific AS (AS1) to pass via 
> AS400-AS20-AS30 as the primary returned path while other AS from the 
> internet cloud would be still the best path going to AS30.

It sounds like what you want is providers who support BGP communities
that would let you tune things like prepending or propagation of routes to 
certain of their peers.  The further away from your network you're trying 
to influence things, the harder its going to be to do.

i.e. if as200 and as300 supported it, you could announce your routes to 
them with tags that say to prepend a few times when advertising to as1, 
making the AS1 - AS400 - AS20 - AS30 path more favorable.

  Jon Lewis                   |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                |
_________ http://www.lewis.org/~jlewis/pgp for PGP public key_________

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