$ ssh -L 8888:www.linuxhorizon.ro:80 user@computer -N $ ssh -L 8888:www.linuxhorizon.ro:80 -L 110:mail.linuxhorizon.ro:110 \ 25:mail.linuxhorizon.ro:25 user@computer -N
The second example (see above) show you how to setup your ssh tunnel for web, pop3 and smtp. It is useful to recive/send your e-mails when you don't have direct access to the mail server.
For the ASCII art and lynx browser fans here is illustrated the first example:
+----------+<--port 22-->+----------+<--port 80-->o-----------+ |SSH Client|-------------|ssh_server|-------------| host | +----------+ +----------+ o-----------+ localhost:8888 computer www.linuxhorizon.ro:80
Have you ever wanted to ssh to your Linux box that sits behind NAT? Now you can with reverse SSH tunneling. This document will show you step by step how to set up reverse SSH tunneling. The reverse SSH tunneling should work fine with Unix like systems.
Let's assume that Destination's IP is 192.168.20.55 (Linux box that you want to access).
You want to access from Linux client with IP 18.104.22.168. Destination (192.168.20.55) <- NAT <- Source (22.214.171.124)
SH from the destination to the source (with public ip) using command below:
$ ssh -R 19999:localhost:22 firstname.lastname@example.org
port 19999 can be any unused port. Now you can SSH from source to destination through SSH tuneling:
$ ssh localhost -p 19999
3rd party servers can also access 192.168.20.55 through Destination (126.96.36.199). Destination:
(192.168.20.55) <- |NAT| <- Source (188.8.131.52) <- Bob's server
From Bob's server:
$ ssh email@example.com
After the sucessful login to Source:
$ ssh localhost -p 19999
The connection between destination and source must be alive at all time. Tip: you may run a command (e.g. watch, top) on Destination to keep the connection active.
Connect to a server:
$ nc hostname port
Be a server:
$ nc -l -p port
Serve a file:
$ nc -l -p port < file
Receive a file:
$ nc hostname port > file
Serve the filesystem:
$ tar cOPp --same-owner / | nc -l -p port
Receive the filesystem:
$ nc -w3 hostname port | tar xPp
Serve the disk image:
$ dd if=/dev/hda | nc -l -p port
Receive the image:
$ nc -w3 hostname port | dd of=/dev/hda
If combining encryption and compression, be sure to compress first then encrypt when sending and reverse the order for receiving. Do not attempt to encrypt then compress. Compression works by finding patterns which are destroyed intentionally by the process of encryption. Also, though not required, specifying the IP address of the host that will be transferring the file is a good idea.
Serving a compresssed, encrypted file from 192.168.0.1 to 192.168.0.2:
$ gzip -c < file | openssl aes-128-cbc -e -k thispassword | nc -l 192.168.0.2 12345
Receiving, decrypting and decompressing that file:
$ nc 192.168.0.1 12345 | openssl aes-128-cbc -d -k thispassword | gunzip -c > file
$ nmap HOSTNAME
$ nc -v -w 2 -z hostname portrange $ nc -v -w 2 -z hostname portlisting
Where portrange is for example "10-20" to scan all ports between 10 and 20, portlisting is for example 11,20,135 will scan these ports.
I just tried this on windows xp, and the comma separated list of ports does NOT work. Instead, use space separated list. eg:
cmd> nc.exe -vv -w 2 -z www.example.com 20-25 79 80 110 137-139 443