Speed Up SSH Connection
Problem
When you need to work on remote environment, chances are high that you need to establish an SSH connection. Slow connection speed can be annoying especially you need to do it very often.
Solution
There are 2 options in ssh_config manual that solve the above problem:
With the above configurations, the subsequent SSH connections have less overhead.
(Your first connection must stay connected for others to reuse the connection)
Here is the explaination of above options from ssh_config manual:
ControlMasterEnables the sharing of multiple sessions over a single network connection. When set to yes, ssh(1) will listen for connections on a control socket specified using the ControlPath argument. Additional sessions can connect to socket using the same ControlPath with ControlMaster set to no (the default). These sessions will try to reuse the master instance's network connection rather than initiating new ones, but will fall back to connecting normally the control socket does not exist, or is not listening.
Setting this to ask will cause ssh(1) to listen for control connections, but require confirmation using ssh-askpass(1). If the ControlPath cannot be opened, ssh(1) will continue without connecting to a master instance.
X11 and ssh-agent(1) forwarding is supported over these multiplexed connections, however the display and agent forwarded will be the one belonging to the master connection i.e. it is not possible to forward multiple displays or agents.
Two additional options allow for opportunistic multiplexing: try to use a master connection but fall back to creating a new one if one does not already exist. These options are: auto and autoask. The latter requires confirmation like the ask option.
ControlPathSpecify the path to the control socket used for connection sharing as described in the ControlMaster section above or the string none to disable connection sharing. Arguments to ControlPath may use the tilde syntax to refer to a user's home directory or the tokens described in the TOKENS section. It is recommended that any ControlPath used for opportunistic connection sharing include at least %h, %p, and %r (or alternatively %C) and be placed in a directory that is not writable by other users. This ensures that shared connections are uniquely identified.