[sophacles]

A lesser known but quite useful bit of ssh is connection multiplexing. Rather than establish a new tcp connection, doing the auth dance, etc, you can tell ssh to reuse an existing connection. (The protocol itself has a notion of channels, a bit of metadata with every data frame to distinguish different streams, and this functionality uses that).

The big thing with it is that you don't have to do a full auth for subsequent sessions - nice if you don't have tmux (etc) on the remote, and do multiple panes via multiple terminal windows. Particularly when auth involves a passphrase and hsm touch or similar that can take several seconds.

It also has a "connection persistence" setting so when you're bouncing around between a handful of servers you don't have to auth each and every time you switch between servers.

Overall I think of it as one of those features that's nice to have, but not really life changing or anything - Some servers I connect to have it turned off and I notice it's absence more than I notice when it's working.

More info: https://en.wikibooks.org/wiki/OpenSSH/Cookbook/Multiplexing

[fanf2]

It makes a huge difference if there’s significant latency between the client and server: ssh is a very chatty protocol, which has not been optimized to reduce round trips like TLS has been - apart from this multiplexing option.

[e12e]

This can make Ansible much more usable when going through (ProxyJump) bastion host.