I ran into something recently that I’d never seen before, and I’m wondering if this is normal or if I’ve just gto a very strange dsl router. Normall I work with dsl modems or dsl PCI cards, so I’m not really sure just what is normal for a dsl router.
I set up a server for a small company here a while back, and since they are kind of far away I set up a remote access using ssh so that I can do maintenance on it with out driving over. That worked easily enough.
Since they had a DSL router, I set up port forwarding in the router to connect the ssh port to the server. As a test, I also forwarded port 80. I removed port 80 after testing. Port 80 showed me something that is really weird.
Using the dsl router and dyndns, I gave the server an address like this “whoever.dyndns.org.” Normally I can then connect from the server to itself using the address. That is, I enter “http://whoever.dyndns.org” into the address bar of a browser on the server and get the web server running on that machine.
Not so on this system. Anyone on the internet who puts the address “whoever.dyndns.org” into their browser would get the web server on our machine. The server can’t address itself by name, however.
After messing with it a while, I came to the conclusion that the browser from the server can connect to the router using the whoever address, but that the router will not route the request back to the server because the request is coming from the server. Addressing the server as “whoever.dyndns.org” works fine from any other pc in the network, so it would seem that the router is refusing to connect a source and a destination that have the same local address.
The router is one that the telekom here provides to their customers. It is an oem unit that has custom firmware from the telekom. I’ve had problems with this kind of equipment from the telekom before, and I wonder if this is one more example of telekom strangeness or if this is normal.