How to use an SSH tunnel to forward ports

Josh Sherman
1 min read
Command-line Interface

Security is important. Bastion hosts (or jump servers) are an easy way to wall off your private servers from the outside world. Improved security is always a good thing, but it isn’t always convenient.

With a bastion host in place, you shouldn’t be able to connect directly to a private resource, like a database server. To connect to a private resource, you can log into the bastion host, and then connect to the private resource from there.

This works well enough, but in a situation when you want to run code on your local machine, and connect to the private resource, this just won’t do.

In that scenario, you can use ssh to forward a port on your local machine to a port on the private server, while routing things through the bastion host to make it all work.

To make this happen, you’ll need to tell ssh a handful of things:

To put all of those words in action, will look something like this:

ssh -N -L LOCALPORT:REMOTESERVER:REMOTEPORT [email protected]

Let’s say we were trying to forward local port 3333 to port 3306 on an RDS MySQL server by way of a bastion host:

ssh -N -L 3333:mydb.us-east-1.rds.amazonaws.com:3306 [email protected]

At this point, if you were to connect to port 3333 on your localhost or 127.0.0.1 you would actually be connecting to port 3306 on your MySQL server.

If you aren’t running MySQL locally, you could swap out 3333 for 3306 and use the same port number locally and on the remote server.

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Husband. Father. Pug dad. Born again Linux user. Founder of Holiday API, Engineering Manager and Emoji Specialist at Mailshake, and author of the best damn Lorem Ipsum Library for PHP.

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