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How does Windows Remote Desktop connection work? An IP address is used to connect to the computer but....how can that IP be accessed from anywhere? If, for example, the IP address is 128.10.10.10, there MUST be another 128.10.10.10 somewhere else in the world. How does Remote Desktop know which one to connect to?

Thanks so much

EDIT: Thank you! Answers cleared this up quite a bit. But if my remote desktop connection suddenly stopped working and I didn't change anything, how do I even start to diagnose what may be the problem? I can remote connect to it from a LAN computer though...

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migrated from stackoverflow.com May 26 '10 at 8:26

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4 Answers

The 192.168....... space is a private network, same like 10.240.....

These are all private networks

10.0.0.0 – 10.255.255.255

172.16.0.0 – 172.31.255.255

192.168.0.0 – 192.168.255.255

So somewhere in your network is a computer with the 192.168.1.55, address, are you using VPN when you use terminal services

Okay I see you changed your question, IP addresses are unique but some ISPs will give you a new IP address every time you connect and recycle those. Because we are running out of IP addresses there is a plan to move to ipv6

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RDC doesn't change this -- NAT translates your local address to the (global) address of the NAT box (which is unique), and gives that as the "reply to" address in the packets it sends out. When packets return, it looks up which internal address goes with that packet, modifies its header, and passes it along to the computer that originally made the request. (Of course, I'm simplifying a bit, but that's the general idea -- in any case, it's the same whether you're using RDC, HTTP, FTP, or any number of other protocols).

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This is probably best suited to superuser or serverfault.

But since you can connect to the machine via the LAN and you have not changed anything then it is likely that the public ip address your ISP assigned you has changed.

Use something like http://whatismyipaddress.com to find out what your public ip address is.

Another possible problem would be if you are behind a NAT router, you will need to tell it that when you connect to the public ip address you infact want the router to forward this connection on to one of your private addresses (the computer you are trying to reach).

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That is your private ip, local to your network only. Your public ip will be assigned to you by your ISP.

If you want to set up your computer so you can use Remote Desktop from anywhere you have a couple options.

  1. Live Mesh or another RDC client
  2. Port forwarding in your NAT/Router.

I've also used dyndns.org in the past along with port forwarding since I don't always remember my external IP address. This will let you associate a dns name with your dynamic IP that you can use to direct to your home network such as "devoted.dyndns.org". Your NAT/Router may even have a field to insert your dynamic dns settings to keep it updated for you (for whenever your ISP hands you a different IP).
It's really a pretty simple setup.

EDIT: Sounds like you have a new question; trouble connecting. Make sure you can ping the IP address you're trying to connect to. Is it on the same network? Different network? Using the public IP address? VPN is connected?

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