How to use SSH to proxy through a Linux jump host


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Safe Shell (SSH) contains a lot of tips up its sleeve. One explicit trick you might not learn about is the flexibility to make use of a bounce host. A bounce host is used as an intermediate hop between your supply machine and your goal vacation spot. In different phrases, you may entry X from Y utilizing a gateway.

There are lots of causes to make use of a bounce server. For instance, Bounce servers are sometimes positioned between a safe zone and a DMZ. These bounce servers present for the clear administration of units inside the DMZ, in addition to a single level of entry. No matter why you may wish to use a bounce server, do know that it should be a hardened machine (so do not simply rely upon an unhardened Linux machine to serve this goal). By utilizing a machine that hasn’t been hardened, you are simply as insecure as should you weren’t utilizing the bounce.

SEE: Info safety coverage template obtain (Tech Professional Analysis)

However how will you set this up? I will present you tips on how to create a easy bounce with the next particulars (Your arrange shall be outlined by your community.):

  • Originating IP:
  • Bounce IP (we’ll name this host-a):
  • Vacation spot IP (we’ll name this host_b):

Configuring the bounce

The very first thing to do is be sure that you’ll be able to SSH from the Originating IP to the Bounce IP after which from the Bounce IP to the Vacation spot IP. As soon as you’re sure of this, configure the bounce. This shall be achieved on the Originating IP. Log into that machine, open a terminal window and subject the command:

sudo nano ~/.ssh/config

In that newly created file, paste the next:

Host host-a
        Consumer USERNAME

Host host_b
        Consumer USERNAME
        Port 22
        ProxyCommand ssh -q -W %h:%p host-a

The place USERNAME is a consumer on host-a and host_b (They do not need to be the identical consumer.). Additionally, you will wish to change the IP addresses to match your wants.

The choices within the above config file are:

  • q – Quiet mode (supresses all warning and diagnostic messages).
  • W – Requests that commonplace enter and output on the consumer be forwarded to HOST on PORT over the safe channel.
  • %h – Host to hook up with.
  • %p – Port to hook up with on the distant host.

Save and shut that file.

Making the connection

To leap out of your Originating IP to Vacation spot IP (by means of the Bounce IP), you merely subject the command:

ssh host_b

You’ll first be prompted for the consumer password on host-a after which for the password on host_b. When you efficiently authenticate each, you may end up on the host_b bash immediate, having made the hop by means of the bounce host.

Making this safer

To make this safer, you may configure SSH key authentication. To do that, it’s good to copy your consumer SSH key from Originating IP to Bounce IP after which copy your consumer SSH key from Bounce IP to Vacation spot IP. Bear in mind, this may be simply achieved with the command:

ssh-copy-id SERVER_IP

The place SERVER_IP is the IP tackle of your server. (Take a look at How one can arrange ssh key authentication ror extra info on tips on how to arrange SSH key authentication.)

Simple leaping

And that’s the way you arrange a primary bounce host with SSH in Linux. Simply bear in mind to ensure your servers are hardened, in any other case utilizing a bounce server will not offer you practically the safety you may want.

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Picture: Jack Wallen

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