Help with port forwarding, it works on the main desktop, not on 2nd computer

[erikiksaz]

Hey all,

Setup:

Uverse 2wire 3600HGV modem/router (wifi disabled) -> Asus RT-N66U. The asus router is DMZ'd under the firewall settings of the Uverse modem/router. Bridge mode isn't an option on the 2wire, so this is the best workaround I was able to find after researching.

Plugged into the Asus router is my desktop computer and also an imac. The imac isn't usually plugged in, but I'm using it for testing, I need to verify that ports UDP 123/500/4500 are open for a T-mobile cellspot signal boosting device.

Anyways, my desktop has an LAN IP of 192.168.2.63, and in the past I've had ports forwarded for multiple games. When I download port-forward programs to test, all the TCP/UDP ports I've previously forwarded for my desktop computer are open. These ports are NOT the same as the 123/500/4500, btw.

The imac has an IP of 192.168.2.50, and has working internet. I set it to forward the UDP 123/500/4500 ports in the same manner as with my desktop, but those ports keep showing as closed! I don't think it's a mac issue because when I plug in the t-mobile boosting device (and also change the port forwarding rules to reflect its new IP), which requires those ports to be open, it can't get a connection to the internet.

I have no idea how else to proceed, I don't understand why one computer has its ports forwarded, but the second connected computer doesn't. I've also tried placing the IP of the imac under virtual DMZ in the Asus settings, but I still don't get open ports.

I appreciate the help, thanks.

 

[Fardringle]

Is there anything listening to those ports on the iMac? And if so, are those ports opened in the Mac firewall (or the firewall disabled)? If not, then you won't get a valid response even if the ports are actually forwarded properly through the routers. To continue the test, try forwarding those ports to the PC that already has working forwarded ports to see if the test ports work there.

 

[master_shake_]

Is there anything listening to those ports on the iMac? And if so, are those ports opened in the Mac firewall (or the firewall disabled)? If not, then you won't get a valid response even if the ports are actually forwarded properly through the routers. To continue the test, try forwarding those ports to the PC that already has working forwarded ports to see if the test ports work there.

this.

had the same problem with an ftp server.

windows firewall was blocking

 

[Mushkins]

It's almost guaranteed those ports are being used by something else or need to be allowed on the firewall level, or both.

UDP 123 is the port used by NTP, which keeps your clock updated.
UDP 500 is used for Internet Key Exchange, which is part of IPSEC.

Why on earth does this thing want those specifically forwarded?

Also keep in mind that if you have duplicate port forwards configured your router isn't going to have a clue what to do with them, and first on the list typically wins. "Opening" a port and forwarding a port are two entirely different things.

If you have a port forward configured for UDP 123 to go to your first PC and then have UDP 123 forwarded to your second PC entered right under it, all incoming UDP 123 traffic is going to strictly be forwarded to the first PC and never get to the second PC.