[c-nsp] Rationale for ISIS default origination behavior

[David Freedman]

>I've been discussing this with some other engineers at work and no one has
>any idea why Cisco would implement it this way.

I doubt many people make use of an IS-IS default (as I'm sure the L1/ATT
behaviour is also seen as an annoyance in modern IP networks), many
networks I've seen running IS-IS and BGP tend to do all their routing in
the iBGP and keep IS-IS for pure infrastructure prefixes (loopbacks and
sometimes transfer networks).

In your scenario, the default can be brought from your external peers into
your iBGP, this would seem quite sensible since you would be avoiding
redistribution and/or conditional default advertisement (which you can
achieve with IS-IS through the use of route-maps).

Dave.