How do I configure my router under another to avoid NAT issues?

Question

I'm sorry if this has been answered before; I tried looking but couldn't find a solution. I'll try and explain as clearly as I can.

I've recently purchased a Rogers Mobile Rocket Hub and it's causing issues with FTP connectivity. Here is our network layout:

• Rocket Hub (gives 192.168.1.1 as LAN IP)

  • Buffalo Wireless Router (192.168.1.2, gives 192.168.0.1 as LAN IP)

    • Comp 1 (192.168.0.3 --- this device has FTP)
    • Comp 2 (192.168.0.4)
    • Comp 3 (192.168.0.5)
    • Etc. etc.

  • Rocket Hub LAN port 2 connects to Buffalo Router WAN port

Normally I would prefer to set the Rocket Hub in bridge mode but that isn't possible. That would not be so much of a problem except that it also cannot assign IP addresses based on MAC addresses...which is what I currently have the Buffalo router doing.

What is the best way to avoid problems with this setup?

------- EDIT -------

OK, so thanks to your help things are working now! Here's the new setup:

• Rocket Hub

  DHCP turned off
  LAN IP = 192.168.0.254
  Port forwarding rules set
  LAN port connected to LAN port of Buffalo Router

• Buffalo Router

  DHCP turned on (serving addresses from .2 > .221)
  WAN IP determined automatically
  LAN IP = 192.168.0.1
  Port forwarding rules not set as they aren't needed (don't know why that is...)

• Devices

  Hooked up to Buffalo Router...gateway, ip all automatically determined via DHCP

Answer 1

Disable DHCP on the RocketHub.
Set the internal IP of the Buffalo to like 192.168.0.2 (or the .2 of whatever subnet the Rockethub uses by default). Set the default route of the Buffalo to point at the internal address of the Rockethub.
Plug the LAN port of the Rockethub into a LAN port of the Buffalo.

That will let the Buffalo still provide DHCP, but all traffic will route through the Rockethub. No more Double-NAT.

Answer 2

On the Buffalo router you should also make sure to limit DHCP to not issue the ip address of the RocketHub router.

Answer 3

You're probably going to have some problems with doing what you want because of artificial limitations in the devices you're working with. Typically I'd just tell you to disable the DHCP server in the Buffalo device, give the Buffalo device's LAN interface an IP address in the 192.168.1.0/24 subnet, and just use the RocketHub device's DHCP server to hand out IP addresses to clients. Since you don't want to use the RocketHub's DHCP server, though, this becomes more problematic.

I haven't worked with this particular Buffalo device. Most little embedded routers that have DHCP servers want to give out whatever IP address is assigned to the router itself as the default gateway. That's problematic in your case. If the Buffalo router lets you configure the default gateway address that its DHCP server hands out then you'd be in business doing the following:

• Disable the DHCP server in the RocketHub devices
• Set the LAN IP address of the Buffalo device to an IP address in the 192.168.1.0/24 subnet (like 192.168.1.2, for example)
• Set the default gateway that the Buffalo device hands out in DHCP to the LAN IP address of the RocketHub device (192.168.1.1)

Clients will obtain DHCP from the Buffalo device in such a configuration, but use the RocketHub device a their default gateway.

If the Buffalo device doesn't allow you to set the IP address handed-out to DHCP clients as the default-gateway then you're probably outta luck. In that case, I'd recommend running a real DHCP server on a PC on your LAN and disabling the DHCP server functionality in the Buffalo device.

If you've got a Linux machine you can run the ISC dhcpd package (which comes in most distributions). There are a variety of free Windows-based DHCP servers. I've used the tftpd32 product with some success, but you can find lots of them to try out.

Finally, if your Buffalo router is supported by OpenWRT (and http://wiki.openwrt.org/toh/start#buffaloyou could replace the firmware and run Linux right on the router. Then you can customize the functionality to your heart's content.