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ssh_config

Configuration you can use in ~/.ssh/config or /etc/ssh_config

Per Host Keys

Host example.com
  IdentityFile ~/.ssh/example.com_id_rsa

Agent Forwarding

Agent Forwarding explained with pictures!

Host *
  ForwardAgent yes

Multiplexing Connections

This is done using a "ControlMaster". This means the first SSH sessions connection will be used for all following ones saving you the connection overhead. Note: when you kill the first connection, all connections will die! Also the first connection won't terminate even if you request it to.

Create directory ~/.ssh/tmp before using below snippet

ControlMaster auto
ControlPath /home/<user name>/.ssh/tmp/%h_%p_%r

If you are using such an SSH configuration and want a real new connection add "-S" to the ssh invocation.

Use Gateway/Jumphost

You can configure jumphosts using ProxyCommand and netcat:

Host unreachable_host
  ProxyCommand ssh -e none gateway_host exec nc %h %p

Automatic Jump Host Proxying

Host <your jump host>
  ForwardAgent yes
  Hostname <your jump host>
  User <your user name on jump host>

Note the server list can have wild cards, e.g. "webserver-* database*"

Host <server list>
  User <your user name on all these hosts>
  ProxyCommand ssh -q <your jump host> nc -q0 %h 22

Automatic Port Knocking

Host myserver
   User myuser
   Host myserver.com
   ProxyCommand bash -c '/usr/bin/knock %h 1000 2000 3000 4000; sleep 1; exec /bin/nc %h %p'