Obviously, when I connect cable modem directly to laptop using LAN cable I can access it ().

But when router is between my laptop and cable modem it's obviously not as easy as that... what I am wondering if there is a general approach on how to solve this? Forward some port on my router so that when I from laptop goes to on my cable modem? How would I configure that on my router?

Router: Asus N66U router with custom Merlin firmware

Cable modem: Motorola SB 6141

3 Answers

I'm confused why your modem would be behind your router, but yes you can do what you are asking by using port forwarding (as you thought you might be able to).

Please note that your question is likely misstated.

The reason why is that the diagram below is the general physical layout for a residential network.

ISP -> coax -> cable modem -> Ethernet -> Router WAN port Router LAN port -> Ethernet -> ComputerA Router Wireless -> 802.11 -> ComputerB

For your router you will need to set up port forwarding so that inbound traffic to the WAN port of your router on a specified port (e.g. 81) is port forwarded to 192.168.100.1 (your modem) on port 80.

To use that you would open your browser and go to the public IP address of the WAN interface on your router on port 81 (i.e. xxx.xxx.xxx.xxx:81) and then your router will forward your traffic to 192.168.100 on port 80.

Instructions on how to configure Asus N66U port forwarding can be found at .

EDIT: I have tested this same network topology and it works without problems for me.

16

Have you actually tried to get there from the inside? Every single router that I've owned knows that if it's not the local network, it goes out the WAN port and takes care of it. I'm running a Ubiquiti Edge Router Lite right now, at home, and I can get to my modem just by putting in the address as if I were plugged into the modem directly. I've tested on the default N66U firmware, and it works (I happen to have one on hand), as well as Linksys default firmware, and an E4200 running DD-WRT, and another running Tomato (Toastman build). If you cannot, I would recommend opening a thread on Merlin's support forums, which looks to be mostly at Small Net Builder ()

I know that's not very helpful, but this should just work without port forwarding, and we can't troubleshoot specific things that may not work based on the whims of a CFW dev.

2

The problem in my case was that I've designated laptop as DMZ... when I access 192.168.100.1 from other machines in my LAN, they can access cable modem dashboard.

Important thing to note, you must ensure that your router sets up LAN differently from cable modem network. My LAN on router is 192.168.10.1/255.255.255.0.

If I had 192.168.100.1/255.255.255.0 or 192.168.10.1/255.255.0.0 on my router, I would obviously not be able to access cable modem dashboard.

Initial/Hacky SSH way:

Hopefully, someone will post instructions on doing this in a better way (by configuring forwarding on router), in the meantime here is what I did:

1. SSH to router IP (I used Putty)
2. Once in command line type:

content=$(wget 192.168.100.1/cmSignalData.htm -q -O -)
echo $content

This showed HTML source of Signal page on Cable Modem dashboard, and it's easy to extract values from there. Obviously is fixed path for Motorola SB 4121, for other cable modems you would need to figure out exact path to signal data by wget 192.168.100.1 and then following HTML source.

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