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Re: Graceful restart - inter-protocol dependencies

Then we are talking about different protocols. I'm specifically referring to RSVP-TE, as defined by RFC 3209.
I am aware that RSVP-TE's signaling mechanism (even just a PathErr message) will probably reach the ingress node long before routing can reconverge. But that's not the question.
The question is, if the node failure is due to a restart, and it has implemented RSVP-TE restart (yes, I'm aware that this is a GMPLS extnsion), but has not implemented graceful restart for any routing protocols, then the originating node won't receive any RSVP-level information about the restarting node. But the IGP will.
We want to prevent the reroute that would normally happen as a result of the route change. Originating nodes can test the LSP using OAM, if there is no other choice, but transit nodes don't have that option. 

Ultimately, this comes down to my original questions:

	Does it make any sense to use RSVP graceful restart in a
	network where graceful restart is not being used for any
	routing protocols?

	If the answer to the previous question is yes, what can be
	done (if anything) to prevent originating and transit nodes
	from rerouting LSPs as a result of the route-table change?

-- David

Jing Ruiquan wrote:

Hi David,

We should specify which version of RSVP we are talking. What I have said is
about GMPLS RSVP-TE as used in ASON. 
When there is a failed link within the network, the ingress node will know
the failure by transport plan OAM mechanism such as SDH path layer AIS, or
by RSVP-TE Notify message. And usually these mechanisms are faster than
routing protocol convergence speed. After the ingress node knows which link
or route has failed, it will do the rerouting while excluding the failed
link or route. 
Hope I say it clearly :-)
Rick 
-----Original Message-----
From: owner-ccamp@ops.ietf.org [mailto:owner-ccamp@ops.ietf.org] On Behalf
Of David Charlap
Sent: Thursday, September 29, 2005 10:35 PM
To: 'IETF MPLS List'; 'IETF CCAMP List'
Subject: Re: Graceful restart - inter-protocol dependencies

But RSVP doesn't work this way.  It is a soft-state protocol.

If the route table changes such that the next-hop interface changes, RSVP is
supposed to reroute the connection accordingly.

This probably won't happen if the next-hop is a strict-hop in an ERO, but it
can easily happen if the next-hop is loose or if the LSP is signaled without
an ERO (meaning routing is consulted to determine the next-hop to the egress
node.)

If there is a paragraph in an RFC that says RSVP-TE should ignore all
route-table changes once an LSP comes up, I missed it.

-- David

Jing Ruiquan wrote:
I think only the originating node should do the rerouting with RSVP-TE .At the same time, all the nodes will converge their IGP routing 

data base.


Rick

-----Original Message-----
From: owner-ccamp@ops.ietf.org [mailto:owner-ccamp@ops.ietf.org] On Behalf Of David Charlap 
Sent: Thursday, September 29, 2005 2:37 AM
To: IETF MPLS List; IETF CCAMP List
Subject: Graceful restart - inter-protocol dependencies
Is there any point to implementing RSVP-TE's graceful restart without also implementing graceful restart for routing protocols?
On the one hand, RSVP doesn't require routing to recover LSPs. It knows the next-hop interface, because of the preserved data-plane 

connection.
Whatever other information it may need, the switch can either preserve this information or recover it from a neighbor using the RecoveryPath object (draft-ietf-ccamp-rsvo-restart-ext-03).
On the other hand, nodes more than one hop upstream of the failure will detect the loss of routing-connectivity to the failed node if IGP graceful restart is not also implemented. They may reroute the LSP away from the failed node, or tear it down altogether, even though the data plane is still active and RSVP graceful restart is recovering the 

control-plane state.
An originating node may consider the destination unreachable, as a result of losing the routes even though the data-plane for the LSP is still up (which can be confirmed via OAM.)
A transit node, when processing an loose ERO-hop, may choose to reroute or fail the LSP if its local topology information says that the failed (and restarting) node is not available. It might even choose to do this for an established LSP, as a result of Path refresh processing. 

My questions are:

1: Does this mean it's pointless to use RSVP graceful restart without
   also using IGP graceful restart (for whatever IGP is active).

2: Is IGP graceful restart sufficient to prevent this problem?  For
   instance, OSPF's restart procedure requires all preserved state to
   be thrown away if a topology change is detected.

3: An originating node can use OAM to validate the data plane of an
   LSP, and choose to ignore what routing tells it about the
   destination's reachability.  But what about transit nodes?  As far
   as I know, MPLS doesn't support segment-OAM, and it would be
   prohibitive for every transit node to run its own OAM streams
   to detect self-to-end connectivity.

4: Are there other solutions to this problem?
One possible solution might be route-pinning, but RSVP doesn't have a built-in mechanism for this. The usual workaround (signal the LSP, requesting route-recording, then turn the RRO into an ERO for subsequent refreshes) can work, but are there situations where even this would be insufficient to prevent a transit node from rerouting/tearing the connection in this particular situation (where RSVP is doing a graceful restart but the IGP is not)? 

-- David