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For the last few months, I've been using a server on my home network for basic backups and hosting some small websites. Up until this past week, I've been using Comcast (cable) as an ISP and now that I've moved into an apartment, I'm using AT&T. (DSL)

I've set up dynamic DNS and I can verify it works externally. However, I can't seem to access the public address from within the local network. Is there something DSL does differently from Cable that makes this frustration possible?

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migrated from serverfault.com Mar 9 '10 at 17:48

This question came from our site for professional system and network administrators.

3 Answers 3

What you want to do is pretty common and should be do-able.

I assume that what you want to do is to access your local server using its public IP from within the local network. I assume that the dynamic DNS resolves correctly from within the local network to its external IP.

There are a number of possible issues. You will need to check them one by one.

  1. You need to make sure that you can ping your server using the local IP. Make sure that there are no connection problems between your local PC and the local server. Sometimes, there may be isolation issues especially if they are connected by wireless.
  2. You need to make sure that you can ping your external IP from your local PC. This will mean that your router can be contacted by your local PC on its external interface and not just the internal one.
  3. Configure your server to be the DMZ of your network and then check that you can still ping it from the outside. Your router should have some sort of DMZ configuration somewhere. Otherwise, you are out of luck.
  4. You need to ensure that your router has its routing tables configured correctly to route packets intended for the external address to the DMZ server. Your router may have some sort of configuration page to add in networking rules.

Hope it helps.

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Did you get a new router when you switched ISPs? It could be that your new router is not clever enough to actually play ping pong with you packets. Either that or the upstream router (which definitely change) isn't.

I'd recommend making your dynamic name the static address of whatever machine is running the web server on your network. Either that or always use the site local IP address instead of the name.

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Before you do any of that, make sure that external requests to port 80 are getting through. You said that you have are using dynamic DNS, so you do not have a static IP address at your location? If not, there is a good chance that your DSL provider is blocking ports to keep you from doing exactly what you are trying to do.

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