Multiple NT DHCP server for different IP submets on the same segment

[Norwich]

Hi,

Bit of an odd one here...


We are running a single subnet network using DHCP to allocate public IP addresses to all machines (except for a few static servers etc). As an aside, we inherited the public IP address installation. Call it 111.111.111.0 (255.255.255.128).

This came with an ISP supplied, locked down internet gateway that is the DHCP server. NOTE: it also uses this DHCP scope to assign 111.111.111.0 addresses to incoming VPN connections.


Now, we changing over to a new ISP,with a sperate firewall/gateway and single public IP address - using 192.168.0.0/24 internally. In order to gradually move over between the two, both subnets and gateways are on the same network segment - the new gateway's internal interface has two IP addresses on both subnets to ease transition.

Now we are at the stage where we need to set up a DHCP server for the 192.168.0.0 subnet, decommission the 111.111.111.0 DHCP server on the internal segment. HOWEVER, we need to keep the 111.111.111.0 DHCP running for the VPN clients running over the old connection for a few more weeks while we gradually migrate them over to the new gateway.


AS the old 111.111.111.0 DHCP server is externally managed we cannot configure it. I'm loathed to ask them to do it as it's only 9-5 support and I want to do this migration out of office hours (obviously). They've been incompetent in the past (one of the resons we've changed ISP) and I wouldn't really trust them to set this up at 4:50pm then have them go home for the weekend...

So what I would like to do is drop a 192.168.0.0 DHCP server on the local segment and for it to have priority over the 111.111.111.0 DHCP server on this segment. I know seperate NT DHCP servers do not co-operate so is there anything I could do to ensure the 192.168.0.0 server fulfils the leases for the VAST majority of clients? maybe some settings to make the new DHCP server respond more quickly?

I maybe able to configure the old 111.111.111.0 DCHP server to some extent as it is accessible remotely via the DHCP admin program but I'm loathed to fiddle around with it too much as it's officially outside of our or responsibilty.

Thanks

 

[Whoheard]

If I understand you correctly, you now have a firewall/ gateway that is performing DHCP for external clients and serving internal clients as well, and now you want to put a DHCP server on the segment. Well this should not be a problem. The firewall/gateway should be able to be configured to ignore DHCP requests from the internal network. Let me know if this is the case.

Bob

 

[Norwich]

Hi,

That's the problem, it's a remotely managed gateway system - with no out of hours support, which is the time I want to do the work

 

[Whoheard]

Do you have smart switch that can filter MAC level? If so, put a block on all ffffffffffff traffic exiting that port. That way none of the DHCP requests will get to the firewall/gateway server. You can put both DHCP scopes on the local segment using your DHCP server. Hope this helps.

Bob

 

[Norwich]

Thanks, I don't think the switch is intellegent enough to filter but I'll check it out.