The MPLS WG Archive

["Vijayanand C - CTD, Chennai." <vijayc@ctd.hcltech.com>]

Katta,

See my comments in line. 
Please correct me if I am wrong.

Regards,
Vijay

-----Original Message-----
From: Katta Sambasiva Rao [mailto:KattaSR@netbrahma.com]
Sent: Friday, September 21, 2001 10:54 AM
To: 'mpls@uu.net'
Subject: CR-LDP doubts


Hi,
I have some doubts about CR-LDP.

1. Suppose a CRLSP is setup with no-pin option and  LSR-A is part of LSP as
loose hop member.
When LSR-A finds better nexthop, it is supposed to taer down LSP along old
path  and send label request to new nexthop. For this, LSR-A has to store
all the TLVs it received in CRLSP initiation request so that it can initiate
request along new nexthop. Does not it imply that CR-LDP is not scalable?

2. We need to maintain state-inforamtion like LSP id and other CRLDP TLVs of
CRLSP in all  LSRs to support LSP updation. With more ingress routers and
more LSPs getting added to MPLS domain, support for updation of LSP seems to
be not scalable. Is my view correct?

Vijay >> Yes. I agree with your view. 

3. When a pinned LSP is pre-empted by high priority LSP request, should it
be re-routed or should be teared down?

Vijay >> I think if you have CSPF running then you can try re-routing 

4. What is the criteria for preemption Suppose there are two LSPs
established with out-interface as interface 2 and hold priority of LSPs is
same. Now I need to preempt one of them to setup new high priority LSP. What
is the procedure for tie breaking. Shall I preempt the one that gives me
required bandwidth or preempt both.

If there are lots of LSPs going out through interface 2 with same priority
but with different bandwidth reservations, deciding which LSP(s) should be
pre-empted seems to be a complex issue. If this is done in propritary way,
the setup and preemption of LSPs may not occur in predictable way.

I think a standard algorithm is required for this decision instead of
everyone doing their own arithmatic in different ways.

Vijay >> I don't see why you should preempt both. I think it is sufficient
to preempt 
the one which just releases the required bandwidth. If you plan to do
rerouting on the 
preempted LSP then that also has to be considered.

5. Is CRLDP draft intended for specifying only encoding of TLVs and a
different draft/RFC is expected about complete CRLDP functionality as the
currect draft does not seem to address many critical and general issues.

6. CRLDP draft has expired. Is it going to be revised.

Vijay >> I fully agree with you that there are a lot unaddressed issues in
the draft. We have 
raised many issues related to CR LDP  which have not been addressed in the
draft.
In this context, people have even asked whether 'CR LDP is dead', since the
draft has not been updated and it is has been given secondary treatment
probably because RSVP-TE is preferred by the giants.



Regards,
Vijay
Core Technologies Division,
HCL Technologies.