ssh <user>@<host> -D<local_port>

<local_port> = local SOCKS proxy port to connect to, eg. 1080

See what’s going on and keep connection alive:

ssh <user>@<host> -v -2 -o TCPKeepAlive=yes -o ServerAliveInterval=10 -o ConnectTimeout=180 -D<local_port> -C sleep 9999999

You may want to while (true); do …; done the sh*t out of this…