Shortening lease on one subnetL: need reduce MCLT for all?
jw354 at cornell.edu
Fri Dec 11 16:19:44 UTC 2015
> On an ISC DHCP server failover pair, version 4.2.5, I need to shorten
> the maximum DHCP lease time for one subnet from 2 hours to 20 minutes
> temporarily to allow the IP address ranges to be expanded. This is
> together with a Cisco ASR9k that I am told is working as a caching
> relay for the DHCP server pair.
> Now it seems reasonable to reduce the MCLT to ten minutes during the
> work. Is that correct? From my understanding, there will be rather
> counterproductive behaviour if the MCLT is left longer than the
> maximum lease: is that not the case?
I think it’s reasonable to design around leases longer than
the MCLT for ordinary use but I don’t think violating that breaks
everything: I imagine it just makes failure recovery less than
We run a shorter lease time than the MCLT regularly, for
clients in our “walled garden”, who we want to force to another
non-walled pool after they register with us, so we give them a
very short lease time. This approach has its own challenges, but
I don’t recall the MCLT discrepancy being any practical concern.
I don’t know anything about caching relays.
Cornell U IT
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