[c-nsp] igp-ldp sync VS ldp session protection

[Oliver Boehmer (oboehmer)]

> I'd like to ask whether there are any gotchas using both at the same
time

nope, these days, both are being used together:

> I see them as complementary technologies
> 
> Using LDP session protection so that labels are retained during the
link
> failure and can be used immediately after the link and IGP comes up no
need
> to wait for LDP to establish session and re-learn labels after link
failure

Right. 
 
> And the artificial igp-ldp sync delay will be introduced only in case
the
> LDP session is lost indeed -e.g. during RSP switchover

Well, that would be one case, but there could also be other, less
obvious/less likely issues which would prevent or delay LDP from
establishing, then IGP would keep advertising a high metric.

But for the most common cases, LDP session protection does the trick
 
> But I guess none of this is needed wen LDP NSR is used right?

well, no, you still need at least one of the two to prevent packet drop
on link-up. NSR/NSF really only addresses RP or process failover.

	oli