jump is a no-authentication ssh daemon that only allows forward TCP channels. Use it to open up an otherwise NAT'd network when you want the entire internet to reach inside it.
jump uses environment variables for configuration; there are two available:
JUMP_LISTEN - specifies where to listen for ssh connections.
Default: random unprivileged port on localhost
JUMP_ALLOW - specifies a network to allow connections to in CIDR notation.
Default: 0.0.0.0/0
Take care when defining JUMP_ALLOW. If left default, you may end up unwillingly creating a global proxy server.
As root, and with openssh moved out of the way, run:
$ JUMP_ALLOW="192.168.1.0/24" JUMP_LISTEN="0.0.0.0:22" jump
2020/08/06 16:49:51 Listening on [::]:22
jump will now allow any forward connection to the 192.168.1.0/24 network
Now, that jump is running, you can use the ssh client's -J parameter to jump though it to another host thats located in the allowed network, e.g.:
ssh -J jumphostname 192.168.1.100
This is not limited to ssh connections, you could also access a http server located in the network:
ssh -L8080:192.168.1.42:80 jumphostname
192.168.1.42:80 is now available on the client's localhost port 8080