Clarification on PARTNER-DOWN and MCLT

[David W. Hankins]

On Thu, Nov 02, 2006 at 08:27:36PM -0800, Ian Anderson wrote:
> The MCLT is used as a lease time to ensure that clients continually
> check in, to check the lease time.  One thing I did not get a chance to
> witness is what is the lease time set to when the primary server is in
> recover-wait mode?  I would think the secondary server would resume
> issuing leases with the dhcpd.conf lease time.  Otherwise what would be
> the point of the primary waiting for MCLT to expire if the secondary is
> still handing out addresses with the MCLT as the lease time?  

In truth what it does is give out:

	max(cur_time, lease.tsfp) + MCLT

> Is the MCLT even relevant when the primary server is truly down and not
> handing out addresses i.e. not just out of contact with the secondary?

Failover does not allow a server to deliver a lease time that is
in excess of MCLT past the potential expiry on the lease or current
time, in any state.


Now, when the server has a peer that is operating in recover or
recover-wait, the servers are communicating via the failover channel.

This means that after a client gets an MCLT lease-time from the
partner-down server, the lease will be acknowledged over the
failover channel, and the potential expiry (tsfp) will be increased
to lease_time+(mclt/2), effectively.

So when the client renews and the two servers are still in this
condition, the partner-down server will be able to give out
lease_time leases.

-- 
David W. Hankins	"If you don't do it right the first time,
Software Engineer		you'll just have to do it again."
Internet Systems Consortium, Inc.	-- Jack T. Hankins