Clarification on PARTNER-DOWN and MCLT

[David W. Hankins]

On Fri, Nov 03, 2006 at 03:43:37PM -0800, Ian Anderson wrote:
> Below is an example of one our lease records.  When reading your
> description of how a "virgin client" obtains a lease and what fields
> change within the lease DB, everything seems to make sense.  The one
> piece that is eluding me is how does having a potential expiry time
> greater than a lease time help in a dhcp-failover environment.  

This ensures that the client will be able to receive the desired lease
time when they renew, since they will renew at 1/2 the previous lease
time (which is what is added to the potential epxiry).

At t=0 (effectively, not directly),

	expires = cur_time + desired_lease_time
	tstp = cur_time + desired_lease_time + desired_lease_time / 2

At t=desired_lease_time/2, the client renews.

'desired_lease_time' remains on the potential expiry on the lease,
so the server is still allowed to give out the desired lease time
(plus fudge up to equal to MCLT).

> How does MCLT "help ensure that any leases the failed server may have
> given out while out of contact with its partner will have expired."

By assuming that all leases in either the FREE or BACKUP state may have
been leased for, at most, a time equal to MCLT beyond the potential
expiry or when the peer was last known to be operating.

> Thanks again for your patience and time. 

No problem.

-- 
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