I have comcast business internet with a single static IP address. I have the SMC3DG gateway and have been using it for a while with no real problems. I previously had a single linux server behind the gateway with the DMZ setup on the gateway to point at this single server. I have added a second server and want to split some of the load. To do this I turned off the DMZ to the original server and setup port forwarding rules. The only problem this seemed to present is that with DMZ turned on port 22 (SSH) was getting forwarded to the linux server, but with port forwarding rules I cannot forward port 22 to a specific server. To overcome this I setup port fowarding rules to forward a different port (2222) from the outside to port 22 on the first server. i then setup port forwarding rules to forward port 3333 to port 22 on the second server. I went on from there to setup several other ports to forward to one of the two linux server. Note the linux servers are at 10.1.10.2 and 10.1.10.3. I have changed the DHCP server on the gateway to start assigning IP addresses at 10.1.10.100 and setup these two linux servers with static IP addresses at 10.1.10.2 and 10.1.10.3. Note before adding the second server, I had the single server setup as a static address at 10.1.10.2, so this is not new with the most recent change.
It seems like it should all work in theory, but here is where it gets strange. Any outside port I forward to the original machine at 10.1.10.2 works great. Any outside port I forward to the new machine will not forward. Note all of the ports and functionals on the second server 10.1.10.3 work great from within the local network. I can ssh to the original machine at 10.1.10.2 via port 2222 and then ssh to the new machine via ip address at port 22 with no problem.
Within the local network I can point my browser at each of the two server on port 80 and get the web server expected from each machine. If I set the port forwarding rule to point port 80 at 10.1.10.2 it works great. If I point the port forwarding rule to point to port 80 at 10.1.10.3 external client timeout.
As a final note, when I click on "Connected Devices" in the configuration screen of the router, I see both of the internal machines on the network.
What next to try?
I should also note that the connection is not refused, but it times out. When scanning the port from outside the location network it indicates as listening, but not data actually gets transferred. Finally should note that all of the machines involved are connected directly to the back of the SMCD3G.
I am getting very tempted to DMZ the SMCD3G and put another router behind the SMCD3G that I trust since DMZ seems to work ok and port forwarding seems to have some kind of problem.
Ok, so I just bought an ASUS RT-68U wireless router and put behind my SMCD3G. I put the SMCD3G into DMZ mode sending all traffic to the ASUS RT-68U. I then use the ASUS RT-68U to direct specific ports to specific machines and it works like a charm. Not sure yet as to the performance impact but am going to play with this later in the week. It works great and gives me a wireless network as well.