Last year I wrote a short article about how to set up SSH port forwarding but I forgot to mention that you can quickly terminate existing port forwardings and create new ones during the SSH connection.
To access required SSH functions you need to use defined escape sequences:
$ ~? Supported escape sequences: ~. - terminate connection (and any multiplexed sessions) ~B - send a BREAK to the remote system ~C - open a command line ~R - Request rekey (SSH protocol 2 only) ~^Z - suspend ssh ~# - list forwarded connections ~& - background ssh (when waiting for connections to terminate) ~? - this message ~~ - send the escape character by typing it twice (Note that escapes are only recognized immediately after newline.)
Port forwarding options:
$ ~C ssh> Commands: -L[bind_address:]port:host:hostport Request local forward -R[bind_address:]port:host:hostport Request remote forward -D[bind_address:]port Request dynamic forward -KL[bind_address:]port Cancel local forward -KR[bind_address:]port Cancel remote forward -KD[bind_address:]port Cancel dynamic forward
Look at the following example to understand it better:
$ ssh somewhere milosz@somewhere's password: XXXXXXXXXX Linux somewhere 3.2.0-4-amd64 #1 SMP Debian 3.2.41-2 x86_64 $
$ ~C ssh> -D 9999 Forwarding port.
$ ~# The following connections are open: #0 client-session (t4 r0 i0/0 o0/0 fd 4/5 cc -1) #3 direct-tcpip: listening port 9999 for 126.96.36.199 port 80, connect from 127.0.0.1 port 44191 (t4 r1 i0/0 o0/0 fd 9/9 cc -1) #4 direct-tcpip: listening port 9999 for 188.8.131.52 port 80, connect from 127.0.0.1 port 44199 (t4 r2 i0/0 o0/0 fd 10/10 cc -1) #5 direct-tcpip: listening port 9999 for 184.108.40.206 port 80, connect from 127.0.0.1 port 44201 (t4 r3 i0/0 o0/0 fd 11/11 cc -1)
$ ~C ssh> -KD 9999 Canceled forwarding.
$ ~. Connection to somewhere closed.
More information can be found in the manual page:
$ man ssh