missing leases

Berg, M. van den mvdberg at nlr.nl
Fri Jun 5 13:41:08 UTC 2009


we are using ISC dhcpd version 3.1.1 in a fail-over, load-balancing
configuration. Using DHCPStatus, we find that in roughly half the
subnets, the number of leases found in the dhcpd.leases file is less
than the number of allocatable IP addresses, as can be calculated from
the pool declarations inside the subnet declarations. Summing up the
statistics collected by DHCPstatus, we find that there are about 2700
leases known in the dhcpd.leases file, while the pool declarations sum
up to about 3700 allocatable IP addresses. Thus more than 25% is not
visible in the dhcpd.leases file.  Is this a normal? I would expect a
much lower number, with a magnitude which is related to the number of
changes in the last minutes.

Perhaps there is a relation with the way that we maintain the dhcpd
configuration files. A script checks every 10 minutes whether the
network configuration database has changed. If so, it generates one file
with all the subnet declarations and one file with all the host
declarations. These files are included into the main dhcpd configuration
file. If the files have been generated, dhcpd is stopped and started. At
both dhcpd servers, the configuration files are maintained in this way.
The two check-and-regenerate scripts do not run simultaneously, but 5
minutes after the other.

Yesterday, at about 16:00 local time, we increased one pool with 150
allocatable IP addresses. This morning, at about 10:00 local time, about
65 of those new addresses are not visible in the dhcpd.leases file.

Meindert van den Berg

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