ssh -L forward multiple ports

Question

I'm currently running a bunch of:

sudo ssh -L PORT:IP:PORT root@IP

where IP is the target of a secured machine, and PORT represents the ports I'm forwarding.

This is because I use a lot of applications which I cannot access without this forwarding. After performing this, I can access through localhost:PORT.

The main problem occured now that I actually have 4 of these ports that I have to forward.

My solution is to open 4 shells and constantly search my history backwards to look for exactly which ports need to be forwarded etc, and then run this command - one in each shell (having to fill in passwords etc).

If only I could do something like:

sudo ssh -L PORT1+PORT2+PORT+3:IP:PORT+PORT2+PORT3 root@IP

then that would already really help.

Is there a way to make it easier to do this?

Answer 1

The -L option can be specified multiple times within the same command. Every time with different ports. I.e. ssh -L localPort0:ip:remotePort0 -L localPort1:ip:remotePort1 ...

Answer 2

Exactly what NaN answered, you specify multiple -L arguments. I do this all the time. Here is an example of multi port forwarding:

ssh remote-host -L 8822:REMOTE_IP_1:22 -L 9922:REMOTE_IP_2:22

Note: This is same as -L localhost:8822:REMOTE_IP_1:22 if you don't specify localhost.

Now with this, you can now (from another terminal) do:

ssh localhost -p 8822

to connect to REMOTE_IP_1 on port 22

and similarly

ssh localhost -p 9922

to connect to REMOTE_IP_2 on port 22

Of course, there is nothing stopping you from wrapping this into a script or automate it if you have many different host/ports to forward and to certain specific ones.

Answer 3

For people who are forwarding multiple ports through the same host can set up something like this in their ~/.ssh/config

Host all-port-forwards
  Hostname 10.122.0.3
  User username
  LocalForward PORT_1 IP:PORT_1
  LocalForward PORT_2 IP:PORT_2
  LocalForward PORT_3 IP:PORT_3
  LocalForward PORT_4 IP:PORT_4

and it becomes a simple ssh all-port-forwards away.

Answer 4

You can use the following bash function (just add it to your ~/.bashrc):

function pfwd {
  for i in ${@:2}
  do
    echo Forwarding port $i
    ssh -N -L $i:localhost:$i $1 &
  done  
}

Usage example:

pfwd hostname {6000..6009}

Answer 5

jbchichoko and yuval have given viable solutions. But jbchichoko's answer isn't a flexible answer as a function, and the opened tunnels by yuval's answer cannot be shut down by ctrl+c because it runs in the background. I give my solution below solving both the two flaws:

Defing a function in ~/.bashrc or ~/.zshrc:

# fsshmap multiple ports
function fsshmap() {
  echo -n "-L 1$1:127.0.0.1:$1 " > $HOME/sh/sshports.txt
  for ((i=($1+1);i<$2;i++))
  do
    echo -n "-L 1$i:127.0.0.1:$i " >> $HOME/sh/sshports.txt
  done
  line=$(head -n 1 $HOME/sh/sshports.txt)
  cline="ssh "$3" "$line
  echo $cline
  eval $cline
}

A example of running the function:

fsshmap 6000 6010 hostname

Result of this example:

You can access 127.0.0.1:16000~16009 the same as hostname:6000~6009

Answer 6

In my company both me and my team members need access to 3 ports of a non-reachable "target" server so I created a permanent tunnel (that is a tunnel that can run in background indefinitely, see params -f and -N) from a reachable server to the target one. On the command line of the reachable server I executed:

ssh root@reachableIP -f -N  -L *:8822:targetIP:22  -L *:9006:targetIP:9006  -L *:9100:targetIP:9100

I used user root but your own user will work. You will have to enter the password of the chosen user (even if you are already connected to the reachable server with that user).

Now port 8822 of the reachable machine corresponds to port 22 of the target one (for ssh/PuTTY/WinSCP) and ports 9006 and 9100 on the reachable machine correspond to the same ports of the target one (they host two web services in my case).

Answer 7

Another one liner that I use and works on debian:

ssh [email protected] $(for j in $(seq 20000 1 20100 ) ; do  echo " -L$j:127.0.0.1:$j " ; done | tr -d "\n")

Answer 8

One of the benefits of logging into a server with port forwarding is facilitating the use of Jupyter Notebook. This link provides an excellent description of how to it. Here I would like to do some summary and expansion for all of you guys to refer.

Situation 1. Login from a local machine named Host-A (e.g. your own laptop) to a remote work machine named Host-B.

ssh user@Host-B -L port_A:localhost:port_B
jupyter notebook --NotebookApp.token='' --no-browser --port=port_B

Then you can open a browser and enter: http://localhost:port_A/ to do your work on Host-B but see it in Host-A.

Situation 2. Login from a local machine named Host-A (e.g. your own laptop) to a remote login machine named Host-B and from there login to the remote work machine named Host-C. This is usually the case for most analytical servers within universities and can be achieved by using two ssh -L connected with -t.

ssh -L port_A:localhost:port_B user@Host-B -t ssh -L port_B:localhost:port_C user@Host-C
jupyter notebook --NotebookApp.token='' --no-browser --port=port_C

Then you can open a browser and enter: http://localhost:port_A/ to do your work on Host-C but see it in Host-A.

Situation 3. Login from a local machine named Host-A (e.g. your own laptop) to a remote login machine named Host-B and from there login to the remote work machine named Host-C and finally login to the remote work machine Host-D. This is not usually the case but might happen sometime. It's an extension of Situation 2 and the same logic can be applied on more machines.

ssh -L port_A:localhost:port_B user@Host-B -t ssh -L port_B:localhost:port_C user@Host-C -t ssh -L port_C:localhost:port_D user@Host-D
jupyter notebook --NotebookApp.token='' --no-browser --port=port_D

Then you can open a browser and enter: http://localhost:port_A/ to do your work on Host-D but see it in Host-A.

Note that port_A, port_B, port_C, port_D can be random numbers except common port numbers listed here. In Situation 1, port_A and port_B can be the same to simplify the procedure.

Answer 9

Here is a solution inspired from the one from Yuval Atzmon.

It has a few benefits over the initial solution:

• first it creates a single background process and not one per port
• it generates the alias that allows you to kill your tunnels
• it binds only to 127.0.0.1 which is a little more secure

You may use it as:

• tnl your.remote.com 1234
• tnl your.remote.com {1234,1235}
• tnl your.remote.com {1234..1236}

And finally kill them all with tnlkill.

function tnl {
  TUNNEL="ssh -N "
  echo Port forwarding for ports:
  for i in ${@:2}
  do
    echo " - $i"
    TUNNEL="$TUNNEL -L 127.0.0.1:$i:localhost:$i"
  done
  TUNNEL="$TUNNEL $1"
  $TUNNEL &
  PID=$!
  alias tnlkill="kill $PID && unalias tnlkill"
}

Answer 10

An alternative approach is to tell ssh to work as a SOCKS proxy using the -D flag.

That way you would be able to connect to any remote network address/port accesible through the ssh server as long as the client applications are able to go through a SOCKS proxy (or work with something like socksify).

Answer 11

If you want a simple solution that runs in the background and is easy to kill - use a control socket

# start
$ ssh -f -N -M -S $SOCKET -L localhost:9200:localhost:9200 $HOST
# stop
$ ssh -S $SOCKET -O exit $HOST

Answer 12

I've developed loco for help with ssh forwarding. It can be used to share ports 5000 and 7000 on remote locally at the same ports:

pip install loco

loco listen SSHINFO -r 5000 -r 7000

Answer 13

First It can be done using Parallel Execution by xargs -P 0.

Create a file for binding the ports e.g.

localhost:8080:localhost:8080
localhost:9090:localhost:8080

then run

xargs -P 0  -I xxx ssh -vNTCL xxx <REMOTE>  < port-forward

or you can do a one-liner

echo localhost:{8080,9090} | tr ' ' '\n' | sed 's/.*/&:&/' | xargs -P 0 -I xxx ssh -vNTCL xxx <REMOTE>

pros independent ssh port-forwarding, they are independent == avoiding Single Point of Failure
cons each ssh port-forwarding is forked separately, somehow not efficient

---

second it can be done using curly brackets expansion feature in bash

echo "ssh -vNTC $(echo  localhost:{10,20,30,40,50} | perl -lpe 's/[^ ]+/-L $&:$&/g') <REMOTE>"
# output
ssh -vNTC -L localhost:10:localhost:10 -L localhost:20:localhost:20 -L localhost:30:localhost:30 -L localhost:40:localhost:40 -L localhost:50:localhost:50 <REMOTE>

real example

echo "-vNTC $(echo localhost:{8080,9090} | perl -lpe 's/[^ ]+/-L $&:$&/g') gitlab" | xargs ssh

Forwarding 8080 and 9090 to gitlab server.

pros one single fork == efficient
cons by closing this process (ssh) all forwarding are closed == Single Point of Failure

Answer 14

You can use this zsh function (probably works with bash, too)(Put it in ~/.zshrc):

ashL () {
    local a=() i
    for i in "$@[2,-1]"
    do
        a+=(-L "${i}:localhost:${i}")
    done
    autossh -M 0 -o "ServerAliveInterval 30" -o "ServerAliveCountMax 3" -NT "$1" "$a[@]"
}

Examples:

ashL [email protected] 6480 7690 7477

ashL [email protected] {6000..6050} # Forwards the whole range. This is simply shell syntax sugar.