Linksys → [Tomato] WRT54GL Tomato - How Do I Access the DSL Modem?

Hi,

I have Tomato running the WRT54GL in PPPoE mode, the Linksys brand DSL modem runs in bridge mode, e.g. as dumb DSL modem only. That works very well.

However, I have a minor problem - I can't access the web interface of the DSL modem.

I set the Linksys IP address to 192.168.23.1, and the DSL modem on 192.168.23.0
When I type 192.168.23.1 into my browser, the Tomato page shows up no problem. However, when I type 192.168.23.0, I get a connection timeout. It's like Tomato is not letting me access that page.

Is ".0" a bad address? Should I use ".2" instead? Or is there some general issue in accessing the DSL modem's web interface when it's in bridge mode?

I want to access it mainly in order to be able to restart it if need be (it's 2km from where I live...), and to check the line quality.

I do not know if Tomato can add a second WAN address, not PPPoE, in the modem subnet. Only a Tomato expert could answer this but I suspect not.

The DSL modem only gives its web page to something inside its own subnet. So the router WAN would have to add a non-PPPoE address at, say, 192.168.23.5 just to talk to the modem (OR a second modem and special routing... OR connecting LAN to WAN with special routing with lots of gotchas... all this is ugly!).

On a secondary note, 192.168.23.0 is invalid IF the subnet is 255.255.255.0. But this is secondary - does that actually work when connected directly to the modem at this address?

The techy reason DSL modems are not easily talked to from the LAN when on the WAN side of a router...

Unlike cable modems, DSL modems have traditionally never performed the special address handling needed to do this. This isn't a surprise since in the DSL case, the WAN packets are PPPoE encapsulated and that PPPoE connection is not talking to the modem (PPP is point-to-point by definition). In the cable modem case, it's comparatively trivial to respond to regular ethernet packets on a special basis and most cable modems do exactly this.

I suggest assigning the modem an IP address on a different subnet then the WRT54GL. Example: 192.168.25.1.

To access the modem, you need to use iptables. Login to the WRT and goto administration --> scripts --> firewall. Copy and paste the commands below into the window, then click save.

iptables -I POSTROUTING -t nat -o vlan1 -d 192.168.25.0/30 -j MASQUERADE
ip addr add 192.168.25.2/30 dev vlan1 brd +

Try it at 192.168.100.1

If the Linksys is downstream from the DSL, then it needs to be on a different subnet.

DSL WAN Public IP
DSL LAN 192.168.1.1
Linksys WAN 192.168.1.2
Linksys LAN 192.168.23.1
PC 192.168.23.101

From the CMD prompt enter
route add -p 192.168.1.1 mask 255.255.255.255 192.168.23.1

This will add a route to your DSL modem. -p means persistent, it will remain after reboot.

Thats not going to work unless the modem passes a private IP to the WRT. The OP did say the modem is running in bridge mode.

If the modem does PPPoE, you can have it do so instead of the WRT. The modem will then pass a public or private IP to the WRT. Doing it this way shouldn't require adding a route or using iptables.

Thanks that worked! Magic! Is there documentation for the above commands? I would like to know more in case I need to troubleshoot things.

One minor hiccup: I had to restart the WRT along the way. Without restart, the change would just not work.
Apparently the routing table change requires a restart even though the WRT doesn't say that explicitly. May have to do with the special nature of this change, I am sure not all routing table changes require a full restart.

Google iptables for documentation on the commands.

I found the commands on another forum (HyperWRT) and simply changed the IPs (192.168.0.0/30 and 192.168.0.2/30). My modem is on 192.168.0.1.

As for having to restart the WRT, I guess it needs to restart to load the changes made to the firewall script.