[j-nsp] uRPF and 0.0.0.0/0

[Chris Adams]

Once upon a time, Clue Store <cluestore at gmail.com> said:
> So im still a little unclear if my config is sane in the fact that I do not
> have a default route pointing to any interface, but I do have a
> 0.0.0.0/0discard as shown below. This is to inject a default inwards
> for OSPF, but
> does not specify an interface. Does this config hose up uRPF (either loose
> or strict)??  I'm hoping Harry will catch this to clarify :)

It shouldn't affect strict mode uRPF, since the route doesn't point to
any interfaces.  However, JUNOS treats _any_ route as valid for loose
mode (unlike IOS that excludes Null0 routes), so a discard or reject
route counts as a valid destination for loose mode.

IIRC though, 0.0.0.0/0 may be special-cased and not counted for loose
mode uRPF.

You could configure 0.0.0.0/0 with "no-install" instead of "discard",
which would mean it doesn't actually get copied to the forwarding table
(so doesn't exist as far as uRPF is concerned).  It can be somewhat
confusing though, as it does still show up in the route table, and only
"show route detail" will show the "NotInstall" flag.

-- 
Chris Adams <cmadams at hiwaay.net>
Systems and Network Administrator - HiWAAY Internet Services
I don't speak for anybody but myself - that's enough trouble.