From ssh2 to openssh

ssh-keygen -i -f id_dsa.pub > id_dsa_open.pub

From OpenSSH to ssh2

ssh-keygen -e -f id_dsa.pub > id_dsa_ssh2.pub

To increase speed on transfer you can force cipher to arcfour.
You can use same mechanism with rsync when you use ssh encapsulation.

scp -c arcfour <source> <destination>

rsync -av -e "ssh -c arcfour -l <username>" <Source> <Destination>

<span style="color:red">NOTE:</span> THis reduce your security though

It is used when you want to forward local port to remote port over SSH.

ssh -f -N -L 5445:localhost:5432 root@<machine>

It is used when you want to forward Remote Port to Local Port.
Usually used to allow access other way around.

ssh -f -N -R 5445:localhost:5432 root@<machine>

Undefine existing value and define new value in session.
This also keep the value same since nothing is changing.

| .screenrc

    unsetenv SSH_AUTH_SOCK
    setenv SSH_AUTH_SOCK $HOME/.screen/ssh-auth-sock.$USERNAME

Each call of screen command will overwrite the existing symlink.

| .bashrc

    _ssh_auth_save() {
            ln -sf "$SSH_AUTH_SOCK" "$HOME/.screen/ssh-auth-sock.$USERNAME"
    }
    alias screen='_ssh_auth_save ; screen'

Now add key to your session with “ssh-add”.
That should do it.

ssh-keygen -lf .ssh/OLD/id_rsa.pub.old