The MPLS WG Archive

["Feng, Mark" <m_feng@trillium.com>]

> -----Original Message-----
> From: Arvind, K [mailto:arvind@tenornetworks.com]
> Sent: Wednesday, November 14, 2001 10:04 AM
> To: 'David Charlap'
> Cc: 'mpls@uu.net'
> Subject: RE: Hello Extension - destination IP address
> 
> The point of contention really was whether it is necessary to 
> stop sending
> Hellos when all of a neighbor's RSVP state  is torn, "since 
> you won't be
> able to tell whether the neighbor went offline, changed 
> address, or simply
> doesn't have state" (quoted from an earlier message in this thread) . 
> I interpreted RSVP state to mean LSP state (for LSPs traversing the
> neighbor). If this interpretation is wrong, then this was the 
> source of
> confusion.
>  If it is correct, I still don't see the need to stop the 
> HELLO protocol
> (except for reasons of CPU/bandwidth conservation, if that is 
> a requirement)
> because "you won't be able to tell whether the neighbor went offline,
> changed address, or simply doesn't have state". There is no such need
> because if a neighbor that is running the HELLO protocol went 
> offline or
> changed address, the HELLO protocol (if left running even 
> after removing all
> LSP state) will detect it. Also, there are mechanisms in the 
> HELLO protocol
> that allow the protocol optionally to go into a suspended state, if a
> neighbor becomes unreachable for whatever reason - this can 
> take care of
> cpu/bandwidth utilization issues, if deployed.
> Regards,
> Arvind
> 

I think, based on the previous discussion, stopping the Hello exchange is to
save CPU/bandwidth. It's been mentioned previously that, even if the Hello
is not stopped, the Hello state machine itself will come to the correct
state.

In case the neighbours are configured, there might be issues related to how
much control/responsibility the user should have, e.g. stopping/re-starting
of Hello.
In case of discovering neighbours by "snooping" messsages received, the
Hello machine is controlled entirely by the implementation. In this case, I
feel you can do either, i.e. stopping/continue when all the states are torn.

One curious thing mentioned above is the "suspension" of Hello. How's that
work? I don't remember seeing that in the RFC. Thanks.

- Mark