bgp as-path info

Tue Sep 2 18:16:48 UTC 2003

If you look closely, they are probably not just stripping your AS. They 
are probably aggregating your network. One provider that I am aware of 
that does this is AT&T. Since your advertisements out the other network 
will be more specific, traffic will only come through them. If the 
networks are the same size, then traffic will most likely come through 
your first provider due to AS path counts.

Usually, you have to request that your more specific routes be allowed 
out due to multi-homing. In the case of AT&T, they have a community that 
you must send with the route to have it sent beyond their local network. 
It's really just a matter of default preference on the part of your 
provider. Some default to advertise more specific while others default 
to advertising their aggregates. The latter is used most commonly when a 
provider does a lot of BGP peering that is not multi-homed. It's not a 
bad policy when it comes to looking at the BGP tables.

-Jack

Austad, Jay wrote:

> I just brought up a BGP session with one of my providers, they are stripping
> our AS as it leaves their network, so it looks like the route is originating
> from their network.  I have another provider that I will be bringing up BGP
> with later this week.  Once I bring up the other provider, I will be
> advertising several networks out both of them.
> 
> Is this as-path stripping going to cause issues?  Does it matter either way?
> 
> -jay