Port forward not working - modem issue?

[barny99]

I am unable to port forward connections to my public IP. I have an Asus router internally, which connects to the internet through a Netgear DM200 modem. I have tried forwarding a variety of ports (both TCP and UDP), none of which appear to be able to establish a connection (ICMP port unreachable), and do not register on the modem's connection/forwarding logs. However, if I enable internet access to the modem's admin interface then I am able to connect to that on the public IP (port 443).

Also, oddly, I can ping the public IP and get a response, even though the modem has 'respond to ping' disabled. While it is possible that this is a modem fault, it seems unlikely, but am unsure what steps to take next.

The combination of modem and router does require port forwarding to be set up on both devices, however I have tested the port forwarding on the router, and that is working fine, so it definitely appears to be an issue with either the modem, or something odd in the EE domain.

The modem appears to be working fine in all other respects. I have reset it more than once, and also updated to the latest firmware.

Any thoughts or advise would be very welcome, cheers!

[XRaySpeX · Accepted solution]

If you are having to set up port forwarding on the modem as well as the router & there is a 'respond to ping' setting on the modem you cannot be using the modem as a pure modem but as a modem router. This will at least cause double NAT issues. Have you tried running the modem as a modem-only?

[barny99]

Thank you, this fixed it! Obviously, I needed to set up my router with the ISP details that had been on my modem, but after a hairy few minutes when nothing seemed to be talking, everything started working. I thought that I had checked for a modem mode previously, but, following your suggestion, found it buried at the end of the config.
I'm still curious as to why the forwarding would not work in router mode, as the functionality should still have been functional - but hey, it's working!

[XRaySpeX]

It was probably the double NAT. You probably could have done it by leaving out the Asus & using the Netgear as a fully-fledged modem router.

Thanks! You're welcome 🙂 ! Glad I could be of assistance & it is now sorted.