DHCP for multiple networks with static and dynamic assignments

Wojciech 'Wheart' Penar wheart at lab103.ict.pwr.wroc.pl
Fri Mar 2 13:00:56 UTC 2007

I'm operating network splitted into few physical networks (sometimes 
containing several logical subnets). There are two DHCP servers working
in fail-over configuration.
Some networks works as "public" so there are no static leases, but more 
often static leases (for permanent users) comes with dynamic pool (for 

Users may migrate between physical networks, and when they use network 
other then their "home" network - they should get an address from dynamic 

I've noticed that when host address is defined statically (host directive)
in one network, dynamic address assigning doesn't work for that host in other
networks - just leaving "no free leases" information in logs. At the same 
time there are about 10 free leases for given subnet on each server, so 
when I remove static address assignment for given host - address is 
assigned and everything works OK.

Log looks like:
Mar  2 13:56:52 server dhcpd: DHCPDISCOVER from 00:16:36:70:f2:34 via 
x.y.z.254: network net_big: no free leases

I'm using ISC DHCPD versions 3.0.1 and 3.0.4 (both linux).

Now my dhcpd.conf looks like:

# some global options

shared-network network_name_n {	# for every physical network
         max-lease-time 86400;
         default-lease-time 43200;

         subnet x.x.x.x netmask 255.255.255.x {
                 option routers x.x.x.x;
                 option broadcast-address x.x.x.x;
                 option domain-name-servers x.x.x.x, x.x.x.x, x.x.x.x;

 		pool {
 			# pool specific options

 	subnet x.x.x.y netmask 255.255.255.x {
                 option routers x.x.x.y;
                 option broadcast-address x.x.x.y;
                 option domain-name-servers x.x.x.x, x.x.x.x, x.x.x.x;

                 pool {
         		# pool specific options

# set of hosts declarations

What I'm doing wrong?

Wojciech Penar

         Wojciech 'Wheart' Penar
  e-mail: wheart.ict.pwr.wroc.pl

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