20 minute leases

Gregory Sloop gregs at sloop.net
Mon Oct 26 15:36:34 UTC 2015

You're looking for something more definitive, it seems - which I don't have. I do believe that quite a lot of work went into fail-over since 4.1 - there are a couple more options that help a fail-over situation survive a peer down situation better [especially in a tight IP pool] and the like. So, I suspect this change also occurred in between. 

But I certainly don't know that's the case, or exactly why. Perhaps someone else will chime in.


  Thanks Greg and Simon.  Things I didn?t find when searching.
   Yes we run failover.  My question was really:  Was this added between 4.1.1 and 4.2.5 ?
   I skimmed the release notes and couldn?t find it.  My users noticed this after the migration from the 4.1.1 server to the 4.2.5 server, so I am thinking the answer is yes.  And I want to explain why it wasn?t happening before but is now.
Don Friesen
From: dhcp-users-bounces at lists.isc.org [mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of Gregory Sloop
Sent: Monday, October 26, 2015 7:22 AM
To: 'Users of ISC DHCP'
Subject: Re: 20 minute leases
This sounds like a fail-over setup, where clients get the MCLT time for the initial lease and then the full lease value after a renewal. This is so that the fail-over servers can communicate and properly handle the client.

[Glenn had a great post I found that explains more about fail-over, MCLT and initial lease times.]




  Hopefully a quick question. We migrated some sites from a few old DHCP servers running 4.1.1 to some not as old servers running 4.2.5.  The users with laptops began complaining about sporadic loss of IP connectivity.  They noticed they were getting 20 minutes leases instead of 24 hour leases.  I watched the traffic and it seems all initial leases to unknown MAC addresses get a 20 minute lease and on renewal get the 24 hour lease.  This is not a complaint, I like the idea of a trial lease.  I just want to verify that the 4.1.1 version did not have this behavior without having to recreate that environment.  I?d like to explain the behaviour to my users with a degree of confidence.

Don Friesen

Gregory Sloop, Principal: Sloop Network & Computer Consulting
Voice: 503.251.0452 x82
EMail: gregs at sloop.net
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