Multi-hop ssh tunnel - howto : Creating a SSH tunnel with port forwarding between multiple hosts

How to create a multi-hop ssh tunnel or how to chain multiple ssh tunnels. (or SSH inception)

For security reasons sometimes you need to jump through hoops in order to connect to a server in SSH and from that server SSH to another server and so on

Consider the following scenario :

  • An application is deployed on a tomcat server on the host3 and listens on the port 8080
  • From my local machine I need to access the tomcat server on the machine host3 but it's not reachable from my machine
  • I need to carry out some tests that need a graphical browser (Firefox, Chrome, etc.)
  • host3 is only accessible from host2which is only accessible from host1

SSH tunneling can help you in this scenario; you can find more information regarding here by forwarding requests on a given port to another port on another machine all through a (or in our case multiple)SSH connection(s)

Below is a graphical representation of what I'm trying to accomplish :

So without anymore delay let's get to it :

All of the following commands are issued from a single terminal, prompt, shell or whatever you want to call it, that needs to remain open to keep alive the tunnels.

1.Connect the local machine to host1 (create the first tunnel)

[ufasoli@local]> ssh -L38080:localhost:38080 ufasoli@host1

2.Connect to host2 from host1 (create the second tunnel)

[ufasoli@host1]>ssh -L38080:localhost:38080 ufasoli@host2

3.Connect to host3 from host2 (create the third and last tunnel)

[ufasoli@host2]>ssh -L38080:localhost:8080 ufasoli@host3

4.Checking the result

Now if everything went as expected you should be able to see your tomcat application by firing your favorite browser with the and entering the target remote URL as a localhost URL with the 38080 port, like for example http://localhost:38080/mywebapp

5.Bonus points

If you prefer you can do all of the above steps in one giant SSH command using the -t flag to chain commands( I also added the -v flag for a more verbose output)

[ufasoli@local]> ssh -v -L38080:localhost:38080 ufasoli@host1  -t ssh -v -L38080:localhost:38080 ufasoli@host2 -t ssh -v -L38080:localhost:8080 ufasoli@host3

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