DHCP Lease Time - 150s

[Colantuoni, Robert]

I have an issue with short lease times being issued, mostly with Cisco VoIP phones. We have a pretty vanilla config, using failover, that boots known hosts from one pool of addresses and unknown hosts from another pool. We also hand out different lease times for known and unknown hosts.

ISC DHCP 4.0.0

Relevant Config Sections:

-- cut --

# LEASE OPTIONS - GLOBAL
default-lease-time 604800;      #  7 days.
max-lease-time 1209600;         #  14 days.
min-lease-time 604800;          #  7 days.

-- cut --

if not known {
        default-lease-time 300;         #  5 minutes
        max-lease-time 300;             #  5 minutes
        min-lease-time 300;             #  5 minutes
}

-- cut --

class "active"   {
        match hardware;
        default-lease-time 604800;      #  7 days.
        max-lease-time 1209600;         # 14 days.
        min-lease-time 604800;          #  7 days.
	 -- cut --
}

We then declare all hosts we know about like this:

subclass "active" 1:00:1e:f7:c2:3e:7e;
host voip-6222 { 
     hardware ethernet 00:1e:f7:c2:3e:7e; 
     -- cut --
}

This has worked well for us for many years, but I've recently seen an issue crop up where the DHCP server is handing out leases of 150 seconds to known hosts that should be receiving 7 day leases.  I thought perhaps this was related to the 300s default above, so I changed it to 400s but the short lease time didn't increase relatively to 200s.

There is nowhere in my config that specifies anything like 150 seconds for a lease! I'm pretty sure the defaults are higher than that also. I've grepped through the source and I didn't see anything obvious. Even more puzzling is that the tstp (the date the DHCP server tells it's failover peer that the lease expires) is correctly 7 days:

lease 10.7.6.61 {
  starts 3 2010/05/26 14:31:33;
  ends 3 2010/05/26 14:34:03;
  tstp 3 2010/06/02 14:32:48;
  tsfp 3 2010/06/02 14:32:48;
  atsfp 3 2010/06/02 14:32:48;
  cltt 3 2010/05/26 14:31:33;
  binding state active;
  next binding state expired;
  hardware ethernet 9c:af:ca:ff:ca:95;
  -- cut --
}

The phones seem to eventually get a 7 day lease, but it's intermittent.

I hope the email provides enough detail... Thanks in advance,

Rob



----------------------------------
Robert G Colantuoni
CIT - Operational Support Services
University at Buffalo
rgc at buffalo.edu
716.645.3552