Ssl – Can Netcat talk to an encrypted port

So, if you scan your system from a system outside your network while netcat is listening to 6666, the outside system sees it's got something running. But when you try from inside your network to connect to your external IP address to route it back in, it's giving an error and netcat shows nothing connecting? I'd almost suspect you're having a routing issue trying to go from your local machine to the router and back in, perhaps a NAT issue with your hardware. What device are you using? You might want to check to see if this is the case by trying to connect to that port (or have a friend try it) from outside your network and see if the result is the same.

The -k option should do the trick.

From the manpage of nc(1):

 -k      Forces nc to stay listening for another connection after its
         current connection is completed.  It is an error to use this
         option without the -l option.

I've noticed the netcat-traditional package on Debian/Ubuntu does not keep listening as it should. In that case use the netcat-openbsd package instead and try again!

Alternatively, use socat, which is more targeted to your usecase of a proxy server. A random TCP-forwarder example from the manpage of socat which needs some modifications of course.

   socat -d -d -lmlocal2 \
   TCP4-LISTEN:80,bind=myaddr1,reuseaddr,fork,su=nobody,range=10.0.0.0/8 \
   TCP4:www.domain.org:80,bind=myaddr2

          TCP  port  forwarder,  each  side  bound to another local IP
          address (bind). This example  handles  an  almost  arbitrary
          number  of parallel or consecutive connections by fork'ing a
          new process after each accept() . It provides a little secu‐
          rity by su'ing to user nobody after forking; it only permits
          connections from the private  10  network  (range);  due  to
          reuseaddr,   it   allows   immediate  restart  after  master
          process's termination, even if some child  sockets  are  not
          completely  shut down.  With -lmlocal2, socat logs to stderr
          until successfully reaching the accept loop. Further logging
          is directed to syslog with facility local2.