Multiple subnets across different vlans

[Glenn Satchell]

Yep, looks like shared-network is wrong for your network layout.

You could also an add "authoritative" statement to the global scope, 
then dhcpd will send a DHCPNAK to those wrong addresses and they will go 
back to DHCPDISCOVER and get a new address on the correct subnet.

regards,
-glenn

On 07/09/11 14:23, Chris Buxton wrote:
> Don't use shared networks for logical networks on two separate VLANs. A shared network (aka multinet or Windows superscope) is when both subnets are on the same VLAN (or the same physical network in the absence of VLANs).
>
> You're getting a DHCP request for an address on one VLAN, but then in parens it lists an address in the other VLAN. Is 172.30.112.121 the address of the DHCP server? I believe you'll see this is from having previously had a shared-network statement wrapped around your subnet declarations. Get rid of the shared-network declaration, and then reboot all your client machines (or otherwise cause them to renew their DHCP leases). Once they all have correct addresses, you shouldn't see any more of these messages, if I'm right.
>
> Regards,
> Chris Buxton
> BlueCat Networks
>
> On Jul 8, 2011, at 5:57 PM, Joshua Beard wrote:
>
>> 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
>>
>>