The mclt statement
jackkiel at netins.net
Tue Nov 11 14:46:54 UTC 2008
I was wondering if someone could explain in a different way (than the
man page for dhcpd.conf) what exactly the mclt statement does.
The information I have from the man page from dhcpd.conf is:
The mclt statement defines the Maximum Client Lead Time.
It must be specified on the primary, and may not be speci-
fied on the secondary. This is the length of time for
which a lease may be renewed by either failover peer
without contacting the other. The longer you set this,
the longer it will take for the running server to recover
IP addresses after moving into PARTNER-DOWN state. The
shorter you set it, the more load your servers will
experience when they are not communicating. A value of
something like 3600 is probably reasonable, but again bear
in mind that we have no real operational experience with
Let's say I set this value to one hour (3600 seconds) and my default
lease time is set at 2 hours (7200 seconds)
In the communications-interrupted mode, if a client wants to renew a
lease that was handed out by the peer server, does dhcp renew the lease,
but only make the lease valid for one hour? If so, once that lease is
requested to be renewed again, will it continue to be renewed for a
lease time of one hour until the other server is back online?
Another way to read that man page snippet from above:
"This is the length of time for which a lease may be renewed by
either failover peer without contacting the other"
Using my numbers from above,
This could also be read that the dhcp server in communications-interrupted
mode will only renew a lease owned by it's partner for a period of one
hour, after that hour is up, it will fail to renew the lease.
I don't think it works that way, but I would like to be sure.
Also, I get the impression that when both DHCP servers are in contact
with one another, mctl is meaningless. It is only in
communications-interrupted and the partner-down states that it is
Finally, what exactly is meant by this statement:
"The longer you set this, the longer it will take for the running
server to recover IP addresses after moving into PARTNER-DOWN state."
Why does the server in the partner-down state have to recover anything?
Doesn't a server in the partner-down state almost behave like a
Thanks in advance,
Jack Kielsmeier <jackkiel at netins.net>
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