Multiple subnets across different vlans

[Joshua Beard]

Hello,

We've recently migrated from dhcp services on a Windows box to using ISC dhcpd on a Linux box.  We have a number of different subnets on their own respective vlans.

Unfortunately, I'm having an issue where using shared-network { } causes clients on different subnets get an address from the wrong subnet.  If I drop shared-network, their addressed are assigned *correctly*, but I get a "wrong network" message in the logs:
Jul  6 16:20:11 ns1 dhcpd: DHCPREQUEST for 172.30.99.62 (172.30.112.121) from 00:50:41:72:5d:01 via eth0: wrong network.

I believe the switches are configured correctly, as it worked as expected on the Windows machines and I get these in the dhcpd log:
Jul  6 20:38:55 ns1 dhcpd: DHCPACK on 172.30.101.145 to 00:25:4b:b8:27:7e (HS01303S4418) via 172.30.96.1 <--

Here's an example of the config:

shared-network douglas {

        include "/etc/dhcp3/dhcpd.reservations.conf";

        subnet 172.30.112.0 netmask 255.255.240.0 {

                range 172.30.115.1 172.30.127.254;
                        option subnet-mask              255.255.240.0;
                        option broadcast-address        172.30.112.255;
                        option routers                  172.30.112.2;
                

        } 

        subnet 172.30.96.0 netmask 255.255.240.0 {

                range 172.30.99.1 172.30.111.254;
                        option subnet-mask              255.255.240.0;
                        option broadcast-address        172.30.96.255;
                        option routers                  172.30.96.1;
        

        } 
}

With this example (using shared-network), clients on the second subnet will get an address belonging to the first.  If I drop the 'shared-network', each subnet assigns correctly, but the "wrong network" error appears on the logs.  I should note that this dhcp server belongs to the first subnet here and only has eth0 configured.

Any hint in the right direction is much appreciated.

Thanks,
Josh