Idea: dynamically create new forwards on existing controlmaster socket to avoid creating netcat process

[moul]

When using a Gateway, the standard behavior is to create a netcat connection on the gateway, by switching to this option we will avoid the creation of new processes on the gateway hosts

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from http://www.openbsd.org/cgi-bin/man.cgi/OpenBSD-current/man1/ssh.1?query=ssh:

-O ctl_cmd Control an active connection multiplexing master process. When the -O option is specified, the ctl_cmd argument is interpreted and passed to the master process. Valid commands are: check (check that the master process is running), forward (request forwardings without command execution), cancel (cancel forwardings), exit (request the master to exit), and stop (request the master to stop accepting further multiplexing requests).