Env: Two Windows 2012 R2 DHCP servers in active/passive (hot standby) mode serving one scope. Scope lease duration: 1 day. MCLT: 1 hour.

Situation: New dhcp client gets IP configuration with a lease duration of 1 day. Upon release, then renew (prior to lease end, as a test) a new IP lease is obtained. However, its duration is 1 hour. Client is always reporting the same DHCP server (primary).

Why is the new lease 1 hour? 1 hour is coincidentally the same as the MCLT, which if I understand correctly is only invoked during a failover condition. No such failover has occurred here.

[Note: I removed the Failover configuration from this scope and the client picks up the correct scope lease time of 1 day.]

  • is the client reporting the correct DHCP server in both cases? – uSlackr Apr 18 '14 at 19:36
  • Yes @uSlackr, I edited the question with that info, too. – jcarpio Apr 18 '14 at 19:37
  • If you increase the MCLT to the desired lease time, in hours, the lease duration will be extended. However this is not recommended by MS. Were you able to find another workaround? – user259250 Dec 11 '14 at 13:29

This is actually correct behavior. It is supposed to prevent a case where your primary server may crash before performing a lazy update to the secondary.

You can read the 5.2.1 section of the dhc failover protocol if you want but the relevant quote is:

"This allows that server to give a longer lease time to the client the next time the client renews its lease, since the time that it will give to the client will not exceed the MCLT beyond the potential expiration time acknowledged by its partner."

  • Ah, that clears things up. There are other (edge) cases (where clients seemed to bounce between 1hr and 1day); but I'll post another question when I can isolate them. – jcarpio Apr 18 '14 at 21:32

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