[j-nsp] as-path-prepend-nerf

[Richard A Steenbergen]

On Sat, Mar 20, 2004 at 06:36:36PM -0500, John Payne wrote:
> 
> --On Friday, March 19, 2004 2:51 AM -0500 Jeff Wheeler <jeff at reflected.net> 
> wrote:
> 
> >                      AS path: 4436 8001 27257 27257 27257 27257 I
> >
> >I'd like to set as-path-prepend-nerf 1 and allow unique ASNs to appear
> >only once consecutively in a learnt path.  The action performed would be
> >to convert the above path to "4436 8001 27257 I."  Is this crazy?  I do
> >not see how this action could introduce loops.
> 
> Wouldn't that defeat the object of the person prepending?

I believe that would be the point. Every network already has final control
of their outbound in the end, so there is nothing new here.

> I'm assuming that if you're doing BGP you're multihomed, so what if you
> see a "natural" 3 or 4 hop path via your other connection?

Using localpref to control outbound traffic between transits (particularly
different "tiers", i.e. multihoming with a tier 1 and other tier 2's who
buy from tier 1's) can be like pounding a nail with a sledgehammer.  
Prepending incoming routes and/or using metric w/always compare med can
help a bit, but breaks down if you have multihomed BGP speaking customers
(and don't want your AS PATHs looking so bad that your customers will
never prefer your routes). Personally I would welcome more tools to play
w/AS PATH in this way, rfc be damned. :)

-- 
Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)