ProxyJump is a newer functionality. There used to be only ProxyCommand. ProxyJump is a shortcut for the usual way to use ProxyCommand to connect through a bastion host but ProxyCommand is more flexible. For example with ProxyCommand you can run any command to connect to the remote host. ProxyJump only connects over ssh. I think I replaced all my ProxyCommand with ProxyJump because I don't need much else than the normal use case.

ProxyCommand allows you to use any command to setup a connection. Not necessarily an ssh command, like ProxyJump. It can be any command, as long as it receives on stdin and produces on stdout, it can act like a TCP connection.

ProxyJump is a special case of `ProxyCommand ssh -p <port> <user>@<host>`. Can't replace the `ssh` in there when using ProxyJump.

I use ProxyCommand to run spipe tunnels for SSH.

You can get a lot more out of ProxyCommand. For example, you can run SSH over non-IP protocols, such as serial, Bluetooth RFCOMM for embedded boards, or vsock for virtual machines without networking set up at all. The latter is built into and setup up automatically by systemd:

https://www.freedesktop.org/software/systemd/man/257/systemd...

I came across ProxyCommand earlier this week, funnily enough. I have Cloudflare Zero Trust set up with an SSH service[0], and have the server firewall drop all incoming traffic. That helps reduce my attack surface, since I don't have any incoming ports open.

[0]: https://developers.cloudflare.com/cloudflare-one/networks/co...

I use ProxyCommand in edge-case devices where key auth is not an option and the password is not controlled by me. ProxyCommand points to a script the retrieves the password from the vault, puts it on the clipboard for pasting, reminds me via stderr it's done so, and then proxies the connection.