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I have a communications application that has a server side component which requires either a known IP address or name (e.g. www.commserver.com) for communications to take place. For communications outside the local area network this must be a publicly visible address. This component will typically run on a clients PC, where they will not have a dedicated server.

The way that I have got around this in the past is to use a DSL account with a fixed IP address and use IP Passthrough on the router to assign this address to a particular client PC. This causes the problem that the PC is no longer visible on the rest of the LAN. I'm sure there is a much easier way of doing this, but don't know how. Any ideas?

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migrated from superuser.com Sep 4 '09 at 12:24

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4 Answers

I am not sure this is the right answer but will give it a stab. You mentioned a fixed IP the only way to get this is to get a fixed IP from your ISP.

However if you need a fixed hostname (more likely) then you use a service such as EveryDNS or DynDNS to get a hostname that will change when your IP address changes.

Also if you are running a firewall/router; you would use Port Forwarding to forward the port to the correct PC. You would need to forward the correct port to the PC.

Finally you could use the DMZ to forward unknown ports but then it is isolated from the other computers on your local network - that is the very definition of a DMZ.

Hopefully that helps but let me know if you have any questions.

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Before I bought a static IP I successfully used a FREE service from no-ip.com The monitor your IP via a tiny application and keep a domain pointed at it. No-IP is very easy to use. –  cop1152 Sep 4 '09 at 14:03
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You can try DynDns. It will enable you to connect your dynamic IP with your DNS address (given to you by DynDns). It only requires small utility on your side at worst. If you have access to router, it gets even easier since almost all routers have support for it.

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Port Forwarding should take care of this for you.

For example, I have an outside static IP of 24.127.38.211. This IP will get you to my router.

Inside my network I have several machine, all with static 'inside' IP's. The address of a particular server is 10.1.10.22. I have config'd my router to send port 3389 to that static IP.

This means that connecting to 24.127.38.211:3389 will send you to THAT machine.

Another example. I have a file-sharing app running on port 333 on a different machine with the static ip of 10.1.10.25. I have created a fordwarding rule to send all requests for port 333 to that IP. So, connecting to 24.127.38.211:333 will send you to the proper machine inside my network.

I am really NOT great at explaining....but Google port forwarding and give it a shot. Unless I am missing something I believe this will help you.

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I think we're missing the second part of his problem:

This causes the problem that the PC is no longer visible on the rest of the LAN.

It sound's like he understands the Port forwarding(IP Passthru), but most firewall do not like when internal clients point at an external address that is then forwarded back through the firewall. What you will need to do is provide a way for the other PC's on the network to resolve the host name to the internal IP address of the PC, while external clients resolve the public IP address. If the network is big enough to have an internal DNS server, this is the easiest option. Since it sounds like you are working on small networks, host files on every PC in the network may be your only option.

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