Accessing a bridged DSL modem from behind a Linksys router

I’ve got a pretty standard home network setup that looks like this, starting from the ISP:

An ISP-provided DSL modem (ActionTec PK5001A if it matters), IP address 192.168.1.1. I followed these instructions to put it in bridge mode.
A Linksys WRT54GL router, IP address 192.168.1.2. It's connected to the modem through its WAN port and the PC through a LAN port.
My PC, IP address 192.168.1.95.

Almost everything is working hunky-dory: I can access the Internet just fine. There is just one piece that’s inconvenient, which is that I can’t access the modem from my PC unless I unplug my PC from the router and plug it directly into the modem.

I’m guessing this is because, being a LAN address, the router tries to route it internally; in particular, the router’s routing table looks like this:

Destination       Subnet mask       Gateway           Interface
207.225. 84. 51   255.255.255.255     0.  0.  0.  0   WAN
192.168.  1.  0   255.255.255.  0     0.  0.  0.  0   LAN & Wireless
  0.  0.  0.  0     0.  0.  0.  0   207.225. 84. 51   WAN

I thought I might be able to fix this by adding a route for destination 192.168.1.1, subnet 255.255.255.255 (I only want to change the route for exactly this IP), gateway 0.0.0.0 on the WAN interface. However, when I try to add that route, the router pops up an error message saying only “Invalid static route!.”

Why is this route invalid? How can I access my modem from my PC without shifting my Ethernet cable from the router to the modem?

There is an existing question that seems quite similar; however, it was marked as a duplicate of a question that no longer appears to exist, so there is no longer an answer to that question.

Daniel Wagner

Posted 2015-09-11T04:33:03.907

Reputation: 903

I checked the duplicate question as well as the supposed duplicate. The duplicate was actually not a duplicate and not relevant to this topic. But both questions looked similar and were from the same user thus moderator error. Will flag for undeletion and cleanup, but I assure you… Nothing in either thread is applicable to this topic. – JakeGould – 2015-09-11T05:34:13.903

One idea: If NAT reflection/loopback is set on the router, then perhaps you can access your modem via your external WAN address? Meaning if your external IP address is 123.456.789.0 then if NAT reflection/loopback is set on the router it should catch that IP and then route you to the modem… If I understand NAT reflection/loopback correctly? And no, 123.456.789.0 doesn’t have to be exposed to the world for this to work I believe. Just try it with your external WAN address on your LAN.

– JakeGould – 2015-09-11T06:01:16.343

What is your goal of accessing the modem on an ongoing basis? Many just directly connect only when they need to change something to troubleshoot. – StackAbstraction – 2015-09-11T15:36:33.543

Is there some reason you have it set up this way? Why did you connect the modem's LAN port to your router's WAN port? This sounds like "I set up my network so my router considers the modem part of the WAN, but I want the modem to be part of my LAN." Umm, you get what you ask for. – David Schwartz – 2015-09-11T15:52:00.053

@DavidSchwartz I'd be happy to set up the network differently, if you have a suggestion. Solutions that don't involve buying more hardware are preferable -- I'd rather swap my Ethernet cable occasionally than pay for another device. The key properties of the setup at the moment is that the router need not be a modem; and the modem need not be a wireless access point. – Daniel Wagner – 2015-09-11T16:16:24.807

@DanielWagner Turn off the router's DHCP server (because you only need one on a LAN) and connect the modem to one of the router's LAN ports. Now the modem and router (which is now just an access point and switch) are on the same LAN. – David Schwartz – 2015-09-11T16:21:18.163

@JakeGould That's an interesting suggestion! I tried visiting the 207 address I have in my question from the router's routing table, which timed out; I also tried my external IP as suggested by a what's-my-ip service, but that seems to trigger a port forwarding rule I have for serving a personal website from my PC. If I turn off the port forwarding rule, I get the router's admin website instead. – Daniel Wagner – 2015-09-11T16:25:50.107

@DanielWagner Well one thing you don’t want is your external IP address to be accessible by anyone in the world! But at least you tried. – JakeGould – 2015-09-11T16:37:05.250

Let's take a huge step back. This might be an XY problem. Why do you want to access your modem? (Also, your modem is not in bridged mode. If it was, it wouldn't have a LAN IP address.) – David Schwartz – 2015-09-11T17:20:13.360

@DavidSchwartz "Why do you want to access your modem?" Because problems happen; if possible, I'd like to put in a little bit of effort now to reduce the effort of troubleshooting later. – Daniel Wagner – 2015-09-11T17:25:37.210

Ahh, that you are using PPPoE in the router is the missing piece. So your modem is routing, but only the PPPoE traffic. Your best bet is probably to leave things the way they are, I'm afraid. Alternatively, you could number the modem into a different subnet and see if the router will let you access it, possibly with an extra static route. – David Schwartz – 2015-09-11T17:49:26.513

Answers

By far the simplest solution is to move your modem or your LAN to a different subnet.

Eg:

Modem: 192.168.1.1
Router: 192.168.2.1

Then it wont have the modem as part of the DHCP pool and will treat it as a remote network (all remote networks go via the same port withe a “router on a stick”).

It’s not uncommon for modems to change over to 192.168.100.1 or similar when bridging for this very reason.

Linef4ult

Posted 2015-09-11T04:33:03.907

Reputation: 3 705

Great suggestion. I'll accept in the next few days when I have a free time slot to check that I can do it and my wife isn't using the connection. – Daniel Wagner – 2015-09-11T16:19:38.693

@DavidSchwartz Is there really double NAT if the modem is in bridge mode? Note in particular that it is the router doing PPPoE, not the modem. The modem is acting only as a translation from phone cable to ethernet cable at the moment. – Daniel Wagner – 2015-09-11T16:30:07.857

@DavidSchwartz No, its not a double NAT setup at all. As per title this is a "BRIDGED DSL modem". When bridged your modem is for the most part a dumb device and has no routing features and you dont really need it as part of the local net. Only reason to access it is for DSL diagnostics, which is fine via the above config. – Linef4ult – 2015-09-12T16:57:17.613

I think, the problem is that you try to create the static route to 192.168.1.1 destination through the port with address 207.225.84.51.

First you should assign to your WAN port IP-address from the 192.168.1.0 subnet or another address; but then you must also change the modem IP. But you can do this only if your router’s firmware supports PPPoE (or another protocol, used by your ISP) with Dual Access (sometimes also called “Russian PPPoE”, “Russian PPTP” etc.). If so, you’d be able to configure router WAN IP separate from the address received by PPPoE connection. Then it would be no problem to create the static route to your modem.

If the official Linksys firmware for this router does not supports Dual Access connections, then you can change firmware to Tomato or DD-WRT, they both supports it.

Update. Also you can first try to change LAN IP of your router to IP from another range, e.g. 192.168.10.1.

JtHermit

Posted 2015-09-11T04:33:03.907

Reputation: 94

Thanks for the suggestion. The router doesn't seem to support dual access. I might look into one of the alternative firmwares, though as I recall the last time I looked at DD-WRT there was a fairly formidable 30-page "absolutely read this entire thing first or you will brick your router" disclaimer. I'm not completely averse to that, but it does make it sort of a backup plan rather than a first choice. – Daniel Wagner – 2015-09-11T16:43:19.897