[c-nsp] I-BGP/IGP question

Nick Hilliard nick at foobar.org
Tue Sep 16 04:42:02 EDT 2014

On 16/09/2014 09:27, Rich Lewis wrote:
> I know this is good practice, but only because I've heard lots of (very
> knowledgeable!) people *say* that it's good practice.

next-hop-self + source-interface lo0 forces the next-hop of the BGP NLRI to
be the loopback interface.  This means that:

1. you can fully delegate the business of optimum next-hop lookup to your
IGP instead of ibgp.  This is a good deal faster.

2. if there is an intermediate interface flap, ibgp will take ages to route
around it and in the interim, routing loops may occur.

3. the bgp best path algorithm uses the igp metric of the bgp next-hop as a
tie-breaker, so you get slightly better control of route policy calculation.

iBGP is designed for heavyweight information carrying, not reacting quickly
to network topology changes.  Best use an igp and depend on recursive route
lookup for that.


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