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I want to configure a dhcp server to assign both public and private IPs. How is the best way to do this? I would like to create a 3-leg network with the public servers in a dmz, but the key thing I am hung up on right now is how to assign both networks IPs through dhcp..

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Are we talking some machines with private IP's and some machines with Public IP's? what is going to be your DHCP server, what OS is your server? tell us more about your network / networks! :) – JamesK Aug 12 '10 at 13:15
hhehe sorry. I'm running windows and trying to configure this through Forefront and windows server DHCP server role. – djmc Aug 12 '10 at 13:23

That's a strange thing you're trying to do there. At any rate, you need to define a scope on the DHCP server for both address ranges and you need a mechanism (DHCP relay agent) for forwarding DHCP broadcasts from the public network to the DHCP server network.

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I came here to echo the strange sentiment. Just assign your DMZ servers static addresses and NAT them with a firewall. You are using a firewall right? – GregD Aug 12 '10 at 13:21
yeah I know it's pretty weird. That's why I came here for direction.. is it unusual to assign public IPs through dhcp? Yes I'm setting up the firewall right now too with Forefront TMG. In forefront, I defined an internal network and a dmz perimeter network that will have the public IPs. – djmc Aug 12 '10 at 13:25
You can NAT your networks with TMG: – GregD Aug 12 '10 at 13:31
Normally you don't give public, internet-facing IP's through DHCP. I suppose you can, but configurations I've seen usually rely on static IP assignments, as unless you own a public block, you're given your public IP by an upstream provider for a reason, and you don't want it accidentally shifting to another system...especially if it's open to public access. – Bart Silverstrim Aug 12 '10 at 13:31
I do have a range of public IPs from my ISP. The reason this is tricky, is because I have a few proprietary devices that can only be assigned IPs through DHCP. I did not make these devices and our vendor doesn't have a web interface for us to utilize yet. These devices need to have public internet IPs. If this is really that unusual a request, then I suppose I can go back and yell at our vendors for being so stupid. But I was hoping the serverfault community could suggest a quickfix wso I could have this up and running this weekend. even if its not the right way. – djmc Aug 12 '10 at 13:42

I would highly recommend "yelling at your vendor" AND/OR looking for another device that can operate with a static IP address.... assigning public IP addresses to your DMZ is VERY dangerous.

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it may be dangerous... but is it possible? I've only setup dhcp servers for internal scopes.. – djmc Aug 12 '10 at 14:03

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