Spontaneously shortened leases

Bob Harold rharolde at umich.edu
Fri Jan 9 21:46:31 UTC 2015

This is partly a guess, but if the "balancing" messages were gone, perhaps
the servers lost contact with each other, and started handing out "mclt"
lease times.  Check what "mclt" is set to - I think an hour is typical.


Bob Harold
hostmaster, UMnet, ITcom
Information and Technology Services (ITS)
rharolde at umich.edu
734-647-6524 desk

On Fri, Jan 9, 2015 at 4:38 PM, Patrick Trapp <ptrapp at nex-tech.com> wrote:

>  We are running a pair of 4.2.7 servers in failover mode. On Christmas,
> we had an issue with the
> clients on the network they support and eventually discovered that the
> servers were handing out leases with 60-second lease times. As a result,
> the servers were swamped with DHCP requests and the clients were unable to
> consistently get and keep an address as the servers were dropping tens of
> thousands of packets a second as every device tried to renew.
> It was noted that the normal "balancing" entries (for failover) in the
> dhcp logs were not present during this time.
> The timestamps on the configuration files where the leases are configured
> were several months old and were still correctly configured for 24-hour
> leases.
> We tried stopping DHCP on each of the servers for a time to see if the
> remaining server would take over without success. Ultimately, we had to
> restart one of the servers itself, not just its DHCP process, to recover.
> Once that was done and the downed server came online, the balancing
> entries were visible in the logs once again and the leases were for 24
> hours instead of 60 seconds. Has anyone else seen this problem? We have had
> no success determining what started this and would prefer to avoid it in
> the future as it took ten days to get all of clients straightened back out.
> Patrick
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> dhcp-users at lists.isc.org
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