The MPLS WG Archive

[Bob Thomas <rhthomas@cisco.com>]

I'd like to correct my prior response to Vach's question.

> Vach,
> 
> > Suppose A sends out a Hello with hold time of 30 seconds on an ethernet
> > interface.  B and C respond, with Hello hold time 20 and 15, respectively.
> > What is the final hold time in hellos sent out by A?
> >  - 15 seconds?  You keep taking the minimum, and B has to adjust down also,
> > since B and C will also form an adjacency?
> 
> Yes.
> 
> >  - 20 seconds with a reject to C, assuming B's hello got to A first?  Why
> > deny C and all who follow?
> >  - 30 seconds, despite B's hello hold time?  That's not what the draft says
> > (although one email in the archive suggests that is the answer).
> > 
> > I'm assuming that A continues to send only one hello message to the
> > multicast group.
> 
> Yes.
> 
> RFC3036 does not explicitly address this case.  That was probably
> an oversight.

The important thing is that A knows that B's hold time is 20 and
C's hold time is 15.  A should use this information to determine
how frequently it needs to send Hello's on the ethernet to keep
discovery adjacencies it cares about alive.

In its Hello's A should advertise the hold time it uses to timeout
discovery adjacencies.

Whether or not A wants to reduce the hold time it uses to timeout
discovery adjacencies based on the knowledge of what the LSR's it has
discovered are using for hold times is an implementation dependent
decision.


Bob