OpenSSH client jump host

ssh-jump-host.md

@@ -0,0 +1,36 @@
+# SSH jump host
+
+Sometimes we can not connect directly to hosts from OpenSSH client. In this situation we can connect over one or more jump hosts to establish the connection.
+
+First of all try to establish the connection via the OpenSSH client to the specific server 
+`ssh -J host1,[host2[,host3]] target`
+> For jump, specify SSH URI in format `[<user>@]host[:port][,<user>@]host[:port]] [<user>]@<host>]`
+> Only for jump, for the target use the regular ways (e.g. `-p` for port).
+
+If it works from the command-line, set it up in the SSH config. It is a good idea to do the individual configurations for the first step for the hosts and after that specify the target.
+
+Place a config file for SSH. By default it is in the `~/.ssh/config`, on windows `%userprofile%\.ssh\config`.
+
+In this example we go to a central host over two jumps. To do this, configure the individual hosts up. Place these lines in the config file.
+```
+Host *
+	ServerAliveInterval 15
+	ForwardAgent yes
+
+Host destination
+	HostName destination.fqdn
+	ProxyJump j1,j2
+	Port 22
+
+Host j1
+	HostName j1.fqdn
+	Port 22
+
+Host j2
+	HostName j2.fqdn
+	Port 22
+```
+
+Next go over the jumps to the destination with the command `ssh destination`. It connects to j1, goes trough this to j2 and jump to destination.
+
+Sources: [ssh(1)](https://man.openbsd.org/ssh), [ssh_config(5)](https://man.openbsd.org/ssh_config#tun-connection)