Berkeley CSUA MOTD:Entry 52962
Berkeley CSUA MOTD
2022/01/18 [General] UID:1000 Activity:popular

2009/5/7-14 [Computer/Networking, Computer/SW/Unix] UID:52962 Activity:nil
5/7     What's a good reverse port forwarding for a PC(inside firewall) ->
        Unix, so that I can VNC into the Unix that gets forwarded to
        PC's VNC server?
           Syntax, to be executed from the PC behind firewall:
           % ssh -R 5900: <destination_server>
           You can also use Putty, by going to Connections->SSH->Tunnels,
           and enter:
                Source port:5900
                Remote (not Local)
                and finally click on Add
           So the connectivity looks like this:
                PC --ssh--> FIREWALL --ssh--> destination_server
           And the resulting "virtual" connectivity:
                PC:5900 <--- destination_server:5901
           With the "-R" argument the destination_server binds to
           port 5901 which will connect back to PC's port 5900. Hence, it's
           a "reverse" tunnel. Note that this can potentially open up
           a lot of problems for companies and is generally frowned
           upon by network administrators. Please use with care.
           \_ Thanks, this is super useful info in general.
        \_ I do this with inetd and netcat.  Just put a line like this in
           /etc/inetd.conf, and reload inetd:
               5900 stream tcp nowait nobody /bin/nc nc YOUR-PC 5900
           You can also do it with ssh port forwarding (e.g. using PuTTY),
           but then you have to remember to keep your ssh connection open
           all the time.
ERROR, url_link recursive (eces.Colorado.EDU/secure/mindterm2) 2022/01/18 [General] UID:1000 Activity:popular

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Cache (2372 bytes)
NAT firewall which needed to be accessible for Remote Desktop. Actually, it was behind 2 NAT devices, but that's sort of irrelevant. After spending a lot of time trying to get the correct ports forwarded, I found out that my ISP was blocking incoming traffic anyways. But this was also problematic, because not only was this computer behind a NAT, but the computer that needed to access it was ALSO behind a NAT. Not to mention, the client computer would be coming from an unpredictable IP address. So my attack plan was to have a third machine sitting on the internet which could act as an intermediary between the client and the remote desktop server. I already had a third machine available, but this was where using SSH tunnels became tricky. So the idea is, you create an SSH tunnel from your computer's port X to a remote server's port Y Any traffic that you send on port X locally will then transparently be sent across the encrypted tunnel to the remote server on port Y Responses will then follow the same path backwards across the tunnel. SMTP This is also very helpful if you need to transport data across a firewall or from behind a NAT device. In order for my setup to work, the remote desktop server would need to be constantly connected to the server in the middle. This way, the client can connect to the middleman at any time and get access to the remote desktop server. A reverse SSH tunnel is exactly like a regular SSH tunnel, except that any traffic that is received on the remote machine gets transparently forwarded to you! com port 4000 (which is our middleman server) to our local port 3389 (which is the remote desktop port). Now when we point our remote desktop client to localhost:4000, the traffic will go across the normal SSH tunnel to the middleman, and then be re-translated across the reverse tunnel to the remote desktop server. The core idea here is that once the traffic on the normal tunnel reaches the middleman, it gets picked up by the reverse tunnel to complete the remainder of its trip. The only last problem was that I needed to keep the reverse tunnel open at all times so that the client could connect whenever it needed to. Permalink Good article, I think to do a remote shell in Putty, go to the same area you would setup local port forwarding and at the bottom of that window check the box for "remote" instead of "local."