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I am trying to connect to my computer in laboratory from home. I have installed Remmina on my laptop home and X11VNC server on the computer in the lab. When I have the laptop in the laboratory I can connect, but when I try it from home I cannot. I do not get any diagnostic messages, just "connection failed".

I figured out that the problem could be that the laboratory network is behind a firewall that prevents the connection from outside the LAN. I have read the documentation on X11VCN and firewalls on:

http://www.karlrunge.com/x11vnc/index.html#firewalls

But, I have no experience with computer networks, so I do not understand what is written there. I tried to learn it by googling the terms I do not understand, but each one leads to many more things I do not understand.

Please could you help me in any way? If there is no simple answer to my question (such as run these commands), could you at least point me to some useful literature or tutorial? I may have to build my knowledge from scratch, since I have no understanding of the most basic concepts such as "port", but learning from Wikipedia seems very confusing.

EDIT: Looking at the comments under How to control an Ubuntu PC from another Ubuntu PC over Internet, using mobile broadband connections? I realized that the IP adresses given in the System settings and the one given by entering "IP address" into Google are not the same. I was using the one given by system settings. I will also try the one given by Google

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If the sys admins in your laboratory are any good, you can't connect to your work PC from home. Firewalls are in place to prevent exactly that.

Ask them about a 'VPN Login' which stands for 'virtual private network'. If they enable that for you, you could connect you PC at home to the network at your laboratory, being 'virtually there'. You could then connect as if you were in the laboratory as you have tested already. (And also ask them how to set up your computer at home to use the VPN.)

If your admins are not good, you could give it a try. You can make a simple test: go to WhatIsMyIPAddress.com from the PC in the laboratory you want to connect to and from another PC in your laboratory. If they both show you the same IP address, you can not connect. (All your laboratory PCs share the same internet IP, so when connecting from the outside, the system doesn't know which one to connect too. You need your admins' help.)

There are ways to circumvent this problems, but they are quite complicated, involve a lot of work on both sides (your PC at home and your laboratory PC), pose a risk to your network infrastructure and you might really get in trouble with your admins. Do you really want to know?

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You are right! All the computers in the lab share the same IP. Thank you! –  Martin Drozdik Jan 21 '13 at 8:29
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The solution would be to create what is known as a '(ssh-)tunnel' between your work PC and your home PC if you want to google that. But it needs to be initiated from your work PC first and involves configuration of the tunnel-endpoint at your home PC. But again: this is probably against the usage policy of your work infrastructure. –  Chaos_99 Jan 21 '13 at 9:20
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