RE: TE metric and graceful restart

[Zafar Ali <zali@cisco.com>]

Dear Kireeti, 

Thanks for the reply; Please see comments in-lined. 

At 10:01 PM 4/27/2002 -0700, Kireeti Kompella wrote:

> On Sat, 27 Apr 2002, Zafar Ali wrote:
>
> > The reason that I understood this as a MAY case is that a node that
> saves
> > bandwidth usage state information locally is able to determine
> (or
> > estimate) the amount of unreserved resources immediately upon
> start-up. In
> > which case it MAY advertise the saved (projected) value(s) during
> the
> > graceful restart period.
>
> Attractive as that may be, life is not so simple.  The process
> of
> recovery for signaling is complex enough without having new LSPs 
> set
> up during recovery.  The idea of discouraging LSPs during recovery
> is
> not just that the recovering node doesn't know its unreserved
> bandwidth,
> but that it wants to complete recovery before setting up new LSPs.
>
> A simple example is that the recovering node X uses per-box labels,
> gets a new LSP request while recovering, and allocates label L to
> that
> request.  But L is already in use for an existing LSP .... 
> One can
> work around this particular example, but keeping it simple seems
> like
> a good initial goal.

Agreed! As I also mentioned that in doing so the node looses
the charm of discouraging other nodes in the network in using it, during
the restart period. This opens doors for some potential race conditions
and scenarios like the one you mentioned in the email. Of course, a node
that may choose to do so has to deal with kind of scenarios that you
mentioned in the email. I see that there are some tradeoffs involved and
the standard should leave a room for exercising such options. Hence, IMO
this should be a local (vendor specific) decision. 

In short, while I am agreeing with the recommendation, I think the
"SHOULD" part should be removed and the standard should leave
it as part of the local decision. 

Thanks

Regards... Zafar 


> At least, that's my take.
>
> Kireeti.
===============
Zafar Ali
Cisco Systems
(734) 276-2459
100 S Main St. #200
Ann Arbor, MI 48104.
email: zali@cisco.com