Nested SSH Connections (Optional)

Overview

Teaching: 0 min
Exercises: 0 min

Questions

• How can I connect to a host machine if I cannot access it directly?

Objectives

• Jump to another host machine within a ssh connection.

You can use ssh inside a ssh connection to “jump” from machine to machine. This sometimes is necessary as not all computers can be connected to directly from the internet. For example, the login node for the KEK computing center cannot be accessed directly if your are not in the KEK network or using a VPN. The KEK network is rather complex so a very simplified layout is shown in :numref:fig:keknetwork.

.. _fig:keknetwork:

.. figure:: keknetwork.png :align: center

Very simplified layout of the KEK network.

Note

It is possible for your home institute to get direct access to a KEK network so you might not be affected by this restriction while at work.

So, unless you are using VPN or are at KEK, you most likely need to connect to the gateway servers first, either sshcc1.kek.jp or sshcc2.kek.jp

ssh username@sshcc1.kek.jp

Warning

Your username on KEKCC is not necessarily the same as your DESY username.

and once this connection is established you can login to KEKCC from this gateway server.

ssh username@login.cc.kek.jp

Warnings

• This second step needs to be done in the terminal connected to the gateway server
• The initial password for login.cc.kek.jp is not the same as that of sshcc1.kek.jp.

Now, you should be connected to KEKCC but you needed to enter two commands. And trying to copy files from KEKCC to your home machine becomes very complicated as you would have copy them in multiple steps as well so, this is clearly not yet the optimal solution.

Key Points

• You can jump between hosts by executing ssh within a ssh connection