# ~/.ssh/config

Host trustedhost.com
        ForwardAgent yes

Host anotherident.com
        IdentityFile ~/.ssh/different_key

Host *
        AddKeysToAgent yes
        ControlMaster auto
        ControlPath "/tmp/ssh-%r@%h:%p"
        ControlPersist 5m
        SendEnv LANG LC_*
        ServerAliveInterval 120