If you want to bind the port 19999 (netdata default port for instance) to port 12345:
ssh -N -L 12345:localhost:19999 $SSH_USER@$SSH_IP -p $SSH_PORT
If you need to execute it in background, simply add the -f flag:
ssh -fN -L 12345:localhost:19999 $SSH_USER@$SSH_IP -p $SSH_PORT
then kill it with kill -9 $PID
(find the PID by typing ps aux | grep ssh