DHCP pair messed up, second one only running cant get primary up.

Rob Morin rmorin at datavalet.com
Sat Jan 14 07:23:22 UTC 2017

Our lease time is governed by our client, which is huge. That cannot be changed. :)

Rob Morin
Gestionnaire des systèmes | Senior System administrator
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-----Original Message-----
From: dhcp-users [mailto:dhcp-users-bounces at lists.isc.org] On Behalf Of Simon Hobson
Sent: Friday, January 13, 2017 3:31 PM
To: Users of ISC DHCP <dhcp-users at lists.isc.org>
Subject: Re: DHCP pair messed up, second one only running cant get primary up.

Rob Morin <rmorin at datavalet.com> wrote:

> Also the dhcpd.leases files grow too big for the /ramdisk, so we are each 10 mins catting /dev/null into /ramdisk/dhcpd.lease! file to save space.

I can't help with the other problems, but pray you don't have to stop the DHCP server at any time before it's re-written the compacted leases file ! Losing the leases file is "bad" in a big way.

I can't help with the specific problem, but I would suggest that if you lengthen the lease time (by a considerable amount) it will dramatically reduce the rate of growth of the leases file. With a lease length of 20 minutes, you'll have a renewal every 10 minutes (roughly) - so that's 6 lease updates to the leases file per hour !

For example, if you were to increase the lease time to (say) 4 hours, then your leases file would contain one record per lease (in practical terms, every address in your pools) plus one update for roughly 1/2 the active clients.

So your lease file size will change from total of IP ranges + 6x number of active clients, to total of IP ranges plus 1/2 the active clients.

Is there a reason for having such short leases ? It's quite short, longer leases bring much stability and much more leeway in dealing with DHCPO service issues !

Also, for consideration, you can have more than 2 servers in failover - but only 2 per pool. So it's possible to have (say) 3 servers sharing the load as A+B, B+C, and C+A. More complexity, but more scope for server failure without losing DHCP service - and more load sharing. Of course, you can also just split pools across an even number of servers as A+B, C+D, etc.

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