[j-nsp] Loop-free Alternate Paths for IS-IS Routes

[sthaug at nethelp.no]

> I'm wondering if anyone here has had any experience configuring the
> loop-free alternate paths for IS-IS in JUNOS, as described in the following
> drafts:
> 
> - Internet draft draft-ietf-rtgwg-ipfrr-spec-base-12.txt, Basic
> Specification for IP Fast-Reroute: Loop-free Alternates 
> - Internet draft draft-ietf-rtgwg-ipfrr-framework-06.txt, IP Fast Reroute
> Framework
> 
> And covered in
> http://www.juniper.net/techpubs/software/junos/junos95/swconfig-routing/jd0e
> 44501.html#jd0e44501.
> 
> I'm looking for general guidance towards implementation, and any caveats
> which might be experienced in a typical deployment.  It seems to me that
> using this, we can entirely get rid of Fast Reroute, or Link/Node protection
> within RSVP/MPLS, but perhaps my understanding is a bit off.

We have tested this in our lab, and expect to deploy it eventually. It
can *not* completely replace Fast Reroute/Link/Node protection, simply
because you are dependent on the paths that your IGP can calculate
(while MPLS Fast Reroute/Link/Node protection, obviously, can use other
paths). What it means in practice is that LFA can not be expected to
give you 100% "fast reroute coverage" for the same topology where MPLS
Fast Reroute/Link/Node protection *can* give you full coverage. There
is a command to show the coverage.

The nice thing about LFA is that it is a completely local optimization,
thus you are not dependent on other routers or protocol changes.

Steinar Haug, Nethelp consulting, sthaug at nethelp.no