[c-nsp] BGP routes co-existing with different local-preference

[Kristian Larsson]

On Thu, Oct 27, 2005 at 03:29:49PM -0400, Alex Rubenstein wrote:
> 
> 
> >> Oh, I've done that.  It's nicer to have just one BGP session when you
> >> have two E1's to one provider (for capacity, not necessarily
> >> redundancy), rather than two eBGP sessions, one on each interface.
> >
> > I've seen Sprint do that across multiple T1's as well. One BGP
> > session for 6 T1 connections.
> 
> It may be nicer, but it's not better.
> 
> Doing one BGP session for multiple physical paths has an inherent danger. 
> Obviously, you have to staticly route the /32 of the far end BGP peer down 
> both paths, and there is always a chance that the physical path may be 
> dead, but show up/up on your router -- if this occurs, you will blackhole 
> approximately 1/n your traffic, were n is the total number of links you 
> have.
> 
> Running BGP between /30's or /31's over each physical path may not be 
> 'pretty' or 'sexy', but it is better.
ip unnumbered over several interfaces is another
solution with no major downsides AFAIK, right? ;)
no multihop and the router wont use interfaces
which are down.

  Kristian.