[c-nsp] HSRp and OSPF metrics

[Phil Mayers]

>>
>> Bearing in mind that changes in externs do not cause an SPF recompute
>> because they are always at the leaves of the tree.
> 
> Because if you source them, they can be included as stubs in the Router
> LSA. Redistributing results in multiple Type 4 (Summary ASBR) and Type 5
> (External) LSAs.  Further, SPF is cheap in terms of CPU cycles.  LSA
> generation and flooding is expensive and is a network wide issue for all
> routers.
> 
> I'd recommend reading "Optimal Routing Design" by Russ White, Don Slice,
> and Alvaro Retana.  http://safari.ciscopress.com/1587051877

Interesting. That's more or less the opposite of what I've understood 
from other sources in the past. I'll take a look, thanks for the pointer.

Having said that, we plan to move away from OSPF to to iBGP carrying 
routes for other reasons.