Is it possible to statically assign public IPs and use DHCP on the same router?

Question

My ISP has given me a set of public IP addresses I can assign to various devices. But they have been controlling everything, and I've had to call them to make any changes to the configuration.

I'm using an airport extreme, though I'd be more than willing to get a DDWRT router going.

Is it possible to, using my router, to assign some public IP addresses while still having a NAT'ed network?

Obviously the devices without public IPs would be on their own network... unless all the public IP devices had a secondary interface.. but I digress.

Answer 1

Do not know about airport extreme, but with ddwrt/openwrt, this should be possible.

Exact config depends on the chosen router, but you can pretty much split the integrated switch into two (either using vlans, or making two bridges). To one of the bridges you will also add WAN port and clients on this bridge will behave as if they were directly connected to the internet.

Then you create second bridge (or use single interface connected to a switch), which will serve as a gateway for NATed clients.

Or you could probably just get a switch, connect it to the internet (if it's ethernet). To this switch you will connect all clients that will have public ip's and the router (even airport extreme will do) that will NAT the rest of the clients.

Edit:

Forgot to add - if you want to do this over wifi, it is possible as well, but you probably need wifi router capable of managing multiple SSIDs.

Answer 2

The easiest way would be to get a secound router. The outer router won't do NAT, and the inner one will. I'll try to illustrate it with a primitive diagram:

Internet ----  Router1 ---- Subnet1 ---- Router2 ---- Subnet2

(Note: From the perspective of Router1 and Subnet1, Router2 is just another machine.)

Subnet1 contains your public-facing IP addresses. Router1 doesn't do NAT, so all the hosts in Subnet1 are directly addressable from the Internet. Router2 has a regular NAT setup. Its WAN port is connected to Subnet1 and has one of your public IP addresses. Its LAN port is connected to Subnet2. The machines on Subnet2 get their IP addresses from Router2 via DHCP. The machines on Subnet1 have static IP addresses, either manually configured or assigned via DHCP by Router1.

If you don't want to get a second router, you can multihome the LAN interface of your router. Assign both a public and a private IP address to the router's LAN port and configure the DHCP server to give out either public or private addresses based on the MAC address of the machines behind the router. But that's complicated to set up, and I don't recommend it unless you're willing to get your hands dirty editing configuration files directly.