[c-nsp] iBGP over IGP with ECMP

[Peter Rathlev]

On Tue, 2011-11-29 at 11:16 -0600, Andrew Clark wrote:
> I'm looking at using iBGP, peered to loopbacks, with EIGRP as my
> "bootstrap" IGP.  I'm assuming BGP will just follow the IGP paths,
> which will be ECMP and the load-balancing will be transparent to iBGP.
> Is this a recipe for disaster?

It'll work fine. Beware though that the hardware based L3 switches use
per-flow load-sharing, not per-packet. That's probably what you want
anyway to avoid out-of-order, but maybe also different from what a
software router (or Dynamips) would do.

> The total size of the routing table isn't too big, around 3K routes.

You might want to play with "sdm prefer ..." on those switches then. The
default ("desktop access IPv4") only allows for 2k routes. Of exceeded
the least specific prefixes will be software switched. That would
probably be a default route, and that one often carries most of the
traffic in a setup with few routes.

Use "sdm prefer routing" to have up to 8k routes.

-- 
Peter