The AskUbuntu question was: How do I SSH to machine A via B in one command?
This response worked for me:
Host <visible hostname alias>
Controlmaster auto
User <user>
hostname <visible hostname>
port <port>
IdentityFile ~/.ssh/<id file>
Host <private LAN hostname alias>
ProxyCommand ssh -q -W <private LAN hostname>:<private LAN port> <visible hostname alias>
Or in my particular case:
Host externalmachine.ca
Controlmaster auto
User externalmachineusername
hostname externalmachine.ca
port 22
IdentityFile ~/.ssh/id_dsa.pub
Host internalmachinehostname
ProxyCommand ssh -q -W internalmachineusername@internalmachinehostname:22 externalmachine.ca