dissecting DHCP - Q4

Defryn, Guy G.P.Defryn at massey.ac.nz
Wed Mar 18 22:19:49 UTC 2009

Thanks Glenn, I gained some more knowledge again.

As a test I brought down my first server. When my lease expires or I renew it,
The second server takes over as expected.
When I bring my first one back online (hours later) and I do a release/renew on the client the lease gets obtained from the first server again.
What is the deciding factor in this and why does the second server not just renew it?
Does the client know its initial lease came from server 1 or is it a "balance" thing?

Ta once more

-----Original Message-----
From: dhcp-users-bounces at lists.isc.org [mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of Glenn Satchell
Sent: Wednesday, 18 March 2009 6:29 p.m.
To: dhcp-users at lists.isc.org
Subject: RE: dissecting DHCP - Q3

Ok, it's slightly more complicated than that. :)

Have a look at the dhcpd.conf man page and scroll down to the sections
titled "DHCP FAILOVER", "FAILOVER STARTUP" and "The mclt statement".

With failover, a server is allowed to hand out a lease of up to mclt
seconds without contacting the other failover peer. So, the dhcp server
hands out an initial lease of mclt seconds. Then the client communicates
this to the partner. This allows the server to respond quickly to the
initial request without waiting for the failover peer to respond. When
the client renews this short lease, if the server has communicated with
the peer, it hands out a lease of default length.


>From: "Defryn, Guy" <G.P.Defryn at massey.ac.nz>
>To: Glenn Satchell <Glenn.Satchell at uniq.com.au>, Users of ISC DHCP 
<dhcp-users at lists.isc.org>
>Date: Wed, 18 Mar 2009 15:58:32 +1300
>Subject: RE: dissecting DHCP - Q3
>Thanks Glenn,
>That makes sense.
>In the mean time the client has obtained a lease for a day but server is still 
in recover state.
>So does it only affect the initial lease time?
>-----Original Message-----
>From: dhcp-users-bounces at lists.isc.org 
[mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of Glenn Satchell
>Sent: Wednesday, 18 March 2009 3:53 p.m.
>To: dhcp-users at lists.isc.org
>Subject: Re: dissecting DHCP - Q3
>>From: "Defryn, Guy" <G.P.Defryn at massey.ac.nz>
>>To: Users of ISC DHCP <dhcp-users at lists.isc.org>
>>Date: Wed, 18 Mar 2009 15:42:29 +1300
>>Subject: dissecting DHCP - Q3
>> Once again thanks for the response to previous questions.
>> Here is the next one,
>> I stopped both my servers and deleted the lease files, created empty lease 
>> and restarted service.
>> My client issued a renewal and picked up lease. What I did notice was
>> That the lease is only valid for 30 minutes.
>> The lease specified in dhcpd.conf is a day.
>> Is this 30 minute lease because it was obtained while my servers are in 
>recover state?
>> cheers
>> Guy Defryn
>Yes, it's the time you set for "mclt" in the failover section of dhcpd.
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