Forwarding WAN incoming to correct LAN

[colecaz]

Diagram attached to help understand this long question.

I have had a network setup with a cable modem followed by a switch which has two routers connected using their WAN ports. When booted up in sequence the cable ISP would allow each router to obtain its own IP address, giving me separate IP's for each router and their LAN. This let me port forward on each router to achieve various functions on the two LAN's.

Now, the cable company will no longer give home accounts two IP's. Not even for $$.

To achieve the same function, can I replace the switch in the above description with a WAN Router and have it port forward a range of ports with no destination port set to the routers connected to its LAN jacks. For example, if an incoming packet has port 1001 set as it's destination, can I set the WAN Router to forward port range 1001:1999 to Router 1 with no destination port in the WAN Router forward instructions? And will the forwarded packet still have port 1001 as it's destination after the WAN Router forwards it so that Router 1 can forward port 1001 to PC1 on port 1001 (or another port if Router 1 translates it)?

This way myhouse.ddns.net:1001 as a address would reach PC1 with the correct translated port number. Say 3389 for Remote Desktop Connection usage. And myhouse.ddns.net:2003 would reach PC3 if the WAN Router forwarded port range 2001:2999 to Router 2.

And from an outgoing side, would double NAT be an issue? Router 1 NAT and then WAN Router also NAT?

Thanks for your comments and patience in reading this long post.

 

[colecaz]

Well, I wired this setup up today and tested it out. Once you get the forwarding right it works fine. Let the WAN Router get an address from the ISP via DHCP and manually set it's LAN address to 192.168.101.1 (or your favorite private address). Then specify a range of IP's for the WAN Router DHCP to hand out to Router 1 and Router 2 for their WAN address. After they get their WAN IP's from the WAN Router DHCP set the WAN Router DHCP to make them static. Now you can port forward individual ports or port ranges from the WAN to Router 1 and 2. The WAN Router forwards any incoming port numbers from the WAN on to the next router for it to send to the PC's according to it's own forwarding instructions if the destination ports are left blank in the WAN router forwarding list.

Undoubtedly there is double NAT going on but so far I haven't seen anything not right because of it. And the PC's get DNS addresses from their routers which in turn seem to get DNS from the WAN router, which gets it automatically from the ISP. Basically, from what I can determine Routers 1 and 2 are seemingly transparent to the PC's except doing the final port forwarding.

So now I've got my two networks connected back to the internet again, this time using only one WAN IP address. It just requires incoming traffic to have a port designated to forward to.