Subject: route pinning - CR-LDP

From: Katta Sambasiva Rao <[email-masked]>
Date: Mon, 30 Jul 2001 18:18:14 +0530

Hi,
I have a doubt in Route pinning of CR-LDP.

Suppose an LSP is pinned to a route. The draft says if there is a new better
route for the established LSP, it should not be considered for pinned LSP.

But if the route becomes completely un-available (say next-hop) failed and
an alternate path which meets LSP requirements exist, what action needs to
be taken. Does the CR-LSP should be teared down as pinning condition cant be
met or the alternate path which meets the requirements should be considered
to set-up LSP from failed point considering the view point that pinning was
for avoiding disruption of services.

problem explained with example: 

A,B,C,D is Explicit route specified, with C as loose hop.
Suppose LSP is set-up with nodes A,B,Z,C,D and pinned.
Now node Z failed, but there is alternate path B,X,C which meets LSP
requirements.
Now what action B should take when it detects it cant reach Z. Should it try
to change LSP path as A,B,X,C,D or tear down the LSP.

If it is implemetation choice, please give your analysis of pros and cons of
each approach.

Thanks in advance.

regards,
Katta

---

From: Eric Gray <[email-masked]>
Date: Mon, 30 Jul 2001 10:28:52 -0400

Katta,

    It is something of an implementation choice, however, opinions on a
'correct' model can be both variant and enthusiastic.  Therefore, it will
make sense to support either approach, optionally, in implementations.

    If you pre-suppose that B has established the alternate path (B-X-C)
in advance, then it must be clear that B assumes a correct behavior that
involves switching to the alternative path.  If you assume otherwise, then
there must be some time-bound criteria on which an operator would like
to see some modification in switching behavior that minimizes lost traffic
and wasted networking resources associated with forwarding packets to
B so that they can be discarded as a result of no extant forwarding path
downstream from B.

    I believe these are the rough parameters defining the domain in which
the two approaches are an implementation choice.

--
Eric Gray