Routing Help...

sancho · 07-13-2006, 05:01 PM

Hey all.

I am trying to make a server on my network available to the Internet so that I may open SSH shells on it from anywhere on the Internet. This used to be an easy setup for me, but I recently changed xDSL providers and, in doing so, have had a slight change in my network topography. This is how my network used to look...

Code:

(INTERNET) <---> [Old Modem]
                 ext: 71.33.23.256 <---> [Linksys Router]
                                         ext: 71.33.23.256
                                         int: 192.168.1.x <---> (Internal Network)
                                                                ssh server: 192.168.1.1

I apologize if the diagram is a bit unclear; the "ext" stands for "external" interface and "int" stands for "internal" interface. The Internet IP address is ficticious. But the main thing to note here is that the Linksys router actually used the modem's IP address (which is an Internet IP). This way, the Linksys router would know the real Internet IP and register itself with DynDNS.org for my domain name.

This is the new setup...

Code:

(INTERNET) <---> [Westell Modem]
                 ext: 71.33.23.256
                 int: 192.168.1.1 <---> [Linksys Router]
                                        ext: 192.168.1.1
                                        int: 192.168.2.x <---> (Internal Network)
                                                               ssh server: 192.168.2.1

As you can see, the new modem still gets an IP on the Internet, but it also supplies the internal interface with an internal address (whereas the old modem used the Internet IP for the internal address). This is a problem for setting up a dynamic DNS service such as DynDNS because the Linksys router no longer knows my real-world IP address. Moreover, it doesn't seem like setting up a simple port-forward on the Linksys router will do anything for me.

This is probably a simple "Routing 101" question for those of you well versed in this area, but if anybody could lend me a hand--preferably somebody with a similar setup--I'd be greatful!

Thanks!

Elomis · 07-13-2006, 05:57 PM

You probably need to have the router in "bridge mode", which means it doesn't take an IP for itself on the internal 192.168.1.0/24 network you have set up, but instead just uses the IP of the "next interface along", that's probably how it was set up before. Have a look on your router for some setting along the lines of "bridge external interface" or "bridge mode".

sancho · 07-15-2006, 10:35 AM

Elomis,

You da man (or woman... or robot)! I've looked up bridging with this particular modem and it can be done. I need to play around with it more, however; when I tried it last night, I lost all connectivity to the modem.

Incidently, when I do get it setup as a bridge and it no longer has an internal IP, how will I be able to log into the modem's configuration program (which used to be at 192.168.1.1)? I expect that I will still be able to login to my router at the same internal address that it's at now since I don't plan on changing it.

Thanks again!

Elomis · 07-15-2006, 08:05 PM

Man, but I'm pretty sure that saying works for any gender.

Yeah that is a pain in the neck, when something is bridged you can't connect to it's IP anymore to manage it because it doesn't have one (an IP that is). Some linksys routers have a way of getting around this by including a program on the CD that comes with them to manage the routers (somehow finding the thing by MAC or whatever) but usually once you bridge it it disappears never to return. I had a bridged network in my last apartment (ISP provided a modem but no router) and if ever I needed to change something I'd hard reset the thing to restore it to factory defaults, make my changes and then bridge it again.

Let me know how it goes.

sancho · 07-16-2006, 06:40 PM

Elomis,

I pulled up a good guide for my particular modem & ISP at this link. It appears that I need to replace my Linksys router's MAC address to that of the modem (makes sense). Both the modem and router appear to be highly configurable, however, and I wonder if I might just be able to change the port of the modem's configuration site to an arbitrary port? This way I could point my browser to my Internet IP using the new port. Currently, both the Linksys router and DSL modem use the standard HTTP port 8080.

I understand nearly everything on the Linksys router's config program pretty well, but the DSL modem has thrown some new settings/terminology at me (like "VC"--whatever that is). That might need to be a new post.

Thanks again.