ssh.md

SSH Port forwarding

SSH opens listens on a specified port and forwards all traffic to a 3rd host and port.

Two types:

• local (-L): the listening port is on the ssh client host
• remote (-R): the listening port is on the ssh server host

Local port forwarding

ssh -L {listen-port}:{target-host}:{target-port} {ssh-server}

localhost            {ssh-server} 
   ssh  ----------->     sshd  

 {listen-port} ------------.
                           |
                           V
                       {target-host}
                       {target-port}

• {listen-port} listens on localhost
• {target-host} is from {ssh-server}'s perspective
• traffic passes via {ssh-server}

Remote port forwarding

ssh -R {listen-port}:{target-host}:{target-port} {ssh-server}

localhost      {ssh-server}
   ssh ------>     sshd

     .-------- {listen-port}
     |
     V
{target-host}
{target-port}

• {listen-port} listens on {ssh-server}
• {target-host} is from localhost's perspective
• traffic passes via localhost

Interactive Port Forwarding

~?   help
~C   command line
~#   list forwarded connections

Example:

~C
-L 8080:localhost:8001

Port 8080 on ssh client is now being forwarded to 8001 on remote.

Misc

ssh-copy-id # copy ssh id to another server ssh-keygen -lf id_rsa.pub # show fingerprint ssh-keygen -E md5 -lf id_rsa.pub # fingerprint with common, one-line syntax ssh-keygen -y -f blah.priv # generate public from private

~/.ssh/config

Host github.com
    IdentityFile ~/.ssh/github

Host bitbucket.org
    IdentityFile ~/.ssh/bitbucket

ssh-keygen -R {host}   # remove all known_hosts entries for {host}