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.

<note important>You can use -v to print random ASCII Image</note>

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

It will print for all public key in single file if there is multiple key in it.
Also, it is usefull in identifying MITM Attack by comparing against your known host.

You can enabled printing of server key by setting following variable.
<note tip>you can setup on any of following file /etc/ssh/ssh_config OR .ssh/config</note>

VisualHostKey yes