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

[Alex Rubenstein]

>> 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.


-- 
Alex Rubenstein, AR97, K2AHR, alex at nac.net, latency, Al Reuben
Net Access Corporation, 800-NET-ME-36, http://www.nac.net