Host bastion.*.i.*.example.net
  User simon.thulbourn
  Port 22
  ForwardAgent yes
  IdentityFile /Users/%u/.ssh/example.net/%r/id_rsa
  UseKeychain yes

Host 10.*
  User simon.thulbourn
  Port 23
  ForwardAgent yes
  StrictHostKeyChecking no
  UserKnownHostsFile /dev/null
  IdentityFile /Users/%u/.ssh/example.net/%r/id_rsa
  UseKeychain yes
  ProxyCommand >&1; h="%h"; exec ssh -q $(ssh-bastion -ip $h) nc %h %p

Host 20.20.20.?
  User simon.thulbourn
  Port 24
  ForwardAgent yes
  StrictHostKeyChecking no
  UserKnownHostsFile /dev/null
  IdentityFile /Users/%u/.ssh/example.net/%r/id_rsa
  UseKeychain yes
  ProxyCommand >&1; h="%h"; exec ssh -q $(ssh-bastion -ip $h) nc %h %p

Host *
  IdentityFile /Users/%u/.ssh/%h/%r/id_rsa
  UseKeychain yes
  Port 25