[c-nsp] Load balancing outbound traffic with BGP

[Pete Templin]

Jeff Chan wrote:

> Given multiple, roughly equal upstreams (Sprint, ATT, Level3)  
> 
> I asked the same question some time ago and the common practice answer  
> seemed to be prefer traffic for some other large networks (UUNet,  
> Qwest, AOL, etc.) over the peers with higher IP address.  Is this  
> still the case?  Seems kind of an ugly hack, but it works.

I'd use prepends so BGP can take over if AS paths should grow due to an 
issue.  For various combinations of two of your three providers, prepend 
1-3 times (1 is probably enough) to some other large networks.

I do something along the lines of:

accept routes generated by the upstream (i.e. Sprint aggregates)
accept upstream's customers' routes (i.e. Sprint customers)
accept routes to be prepended 3x
accept routes to be prepended 2x
accept routes to be prepended 1x
accept all other routes

on a per-neighbor basis.

(For what it's worth, I keep two additional copies of each route map 
standing by, one labeled -highmed and one -maint.  The highmed probably 
doesn't apply in your case, but it sticks a high med on all routes so 
traffic shifts off to parallel links to the same provider, and maint 
applies more prepends and lower localpref so that it's a fallback route 
if needed but isn't likely in steady state.)

pt