[c-nsp] Conditional BGP

[Pete Templin]

Paul Stewart wrote:

> What is common practice for this scenario?  We would still prefer to just
> send a full table and put the control into their hands but I'm also
> concerned if they will have the technical expertise to accomplish this..  On
> their side, what would be common practice?  I've been looking at conditional
> BGP advertisements using route-maps but don't believe that's the best
> solution..

They can control their outbound fairly easily.  They should make sure 
they're getting the same level (default-only, partial, full) of routes 
from you as from Cogent - if they take more from you, those routes are 
more-specific and would win regardless.  I'd suggest they take 
default-only from you (or more but filter out everything but default so 
they can change on the fly later) and whatever they wish from Cogent.

Controlling inbound is often tougher.  Any smart provider sets a higher 
local pref on customer routes than on transit/peer routes (make money 
rather than pay money), so if you do this you'll need to make an 
exception for them (or offer the exception via communities).  Otherwise, 
you'll prefer their announcement no matter how many prepends they do, 
and if that happens for a minute, your transits will likely prefer your 
propagation no matter how many prepends they do.  Even if you don't do 
this today, if Cogent goes down, you'll choose the direct link (it's the 
only one live) and your transits will do the same thing (your routes 
have customer LP in their network).  When Cogent comes up, your transits 
will ignore the Cogent-propagated route since it's only peer LP.  They'd 
have to bounce the link to you to restore their preferred balance. 
You'll need to find out how to accomplish the same thing in your 
providers' networks as well.  (Been there, done that, got the t-shirt.)

pt