I would like to forward all ports from the Technicolor TC7200.U modem to my router, but as soon as I try to forward a port range of more than one port, I get a message as seen in screenshot 1.
My first question is: What does this mean: "In DS-Lite mode, IPv4 forwarding is only allowed for single port settings"?
Anyway, after that message I decided to forward just a few selected ports, to test (as seen in screenshot 2), but somehow my packets don't get passed on to my router behind (I tried a netcat on port 1234, but nothing would happen, and even iptables doesn't give me any indication that any packets other than the ordinary broadcast packets are arriving).
This brings me to my second question: Do I need to do something more than just click on "save" in order for the forwarding rules to take effect?
And last but not least, in the main status view, there is a line "CM IP Address", with an IP address in the 10.0.0.0/8 range, which I assume is *not* my public IP address. I cannot find my public IP address anywhere in that admin interface, so I just had a quick look what the outside world sees me as, and I see an address in the 184.108.40.206/17 range, which seems to be part of "upc cablecom GmbH" (which is probably fine).
This brings me to the conclusion that somehow Cablecom is NATing my connection. I really, really hope that I'm wrong, for the sake of all things holy, but it would perfectly explain the behaviour described above.
Could someone please shed some light on these matters? Thanks in advance!
Alright, so all of this starts to make sense after reading https://en.wikipedia.org/wiki/IPv6_transition_mechanism#Dual-Stack_Lite_.28DS-Lite.29.
The 10.0.0.0/8 is an address in the private Cablecom network, and indeed connections over IPv4 are NATed, whereas connections over IPv6 should allow me to access the modem directly.
Sorry for the noise. I'll be back to report how exactly things need to be set up for a router behind the modem.