Comment by ta1357

Don't do that. Do this instead (taken from my ~/.ssh/config):

  # Sample bastion host configuration without ForwardAgent
  # Host bastion
  #       User bastion_user
  #       Hostname 10.11.12.13
  #       IdentityFile ~/.ssh/id_bastion
  #
  # Host server
  #       User server_user
  #       Hostname 192.168.0.1
  #       IdentityFile ~/.ssh/id_server
  #       ProxyCommand ssh -q -W %h:%p bastion