The MPLS WG Archive

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

I agree with most of the comments; but I have one doubt. Please see comments
below.

- Mark

> -----Original Message-----
> From: David Charlap [mailto:David.Charlap@marconi.com]
> Sent: Tuesday, November 13, 2001 9:35 AM
> To: 'mpls@uu.net'
> Subject: Re: Hello Extension - destination IP address
> 
> 
> "KHARE,MADHUKAR (A-NewEngland,ex1)" wrote:
> > 
> > This is regarding the Hello extension for RSVP.  We are unsure what
> > to use for the destination IP address for a Hello Request message.
> > 
> > The draft just says "The IP destination address is the IP address
> > of the neighbor node".  When the first Hello Req is sent out, we
> > don't know the address of the neighbor node".
> > 
> > Are we supposed to use a broadcast IP address first time around?
> 
> No.  Hellos are not sent to broadcast addresses.  They are 
> not used for
> discovering neighbors.
> 
> If your router doesn't have neighbor addresses configured, then you
> won't know your neighbor addresses until after you receive 
> other packets
> from them - like Path and Resv messages.  Once you know the 
> address, you
> can begin sending Hellos.
> 
> If you do this (discovering neighbors for Hellos by snooping 
> other RSVP
> packets), then you may want to stop sending Hellos when the all of the
> 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.
> 

Why is it necessary to stop sending the Hello in this case? IMO, the way the
Hello state machine works is independant of the means to discover the
neighbour. Even if the neighbour's RSVP states are gone, the neighbour
should still respond to the Hello messages. This should be applicable in the
case when the neighbour is configured.

By stopping the Hello exchange, the neighbour might incorrectly think that
there is a problem communicating with the current node.
 
> -- David
>