
  +-----------------+  NAT                               Firewall +--------------------------+
  |                 |  ||                                   ||    |                          |
  |    web browser  +--OO---------------------------------->XX    + 0.0.0.0:80 web server    |
  |                 |  ||                                   ||    |                          |
  |                 |  ||   +--------------------------+    ||    |                          |
  |                 |  ||   |                          |    ||    |                          |
  |                 |  ||   |      [ ssh server ]      |    ||    |                          |
  |      ssh client +--OO-->+ 0.0.0.0:22    0.0.0.0:22 +<---OO----+ ssh client               |
  |                 |  ||   |                          |    ||    |                          |
  |                 |  ||   |               ssh client +--->XX    + 0.0.0.0:22 ssh server    |
  |                 |  ||   |                          |    ||    |                          |
  +-----------------+  ||   +--------------------------+    ||    +--------------------------+

      My Notebook                  Public Server                         Private Server
       localhost                IP address : A.B.C.D                  ( private IP address )

                                       |||                              on Private Server
                                       |||                            run following commands
                                       |||           'nohup ssh -f -N -R 10000:localhost:22 user@A.B.C.D'
                                       |||                            to generate forward ****
                                       |||
                                      VVVVV   'nohup ssh -f -N -R A.B.C.D:8123:localhost:80 user@A.B.C.D'
                                       VVV                            to generate forward ====
                                        V

  +-----------------+  NAT  +--------------------------+ Firewall +--------------------------+
  |                 |  ||   |                          |    ||    |                          |
  |    web browser  +--OO-->+ A.B.C.D:8123             +==+ || +==+ 0.0.0.0:80 web server    |
  |                 |  ||   |                          |  | || |  |                          |
  |                 |  ||   |      [ ssh server ]      |  | || |  |                          |
  |      ssh client +--OO-->+ 0.0.0.0:22    0.0.0.0:22 +<-+-OO-+--+ ssh client               |
  |                 |  ||   |                          |  | || |  |                          |
  |                 |  ||   |    +--------  ssh client |  | || |  |                          |
  |                 |  ||   |    |                     |  | || |  |                          |
  |                 |  ||   |    +---> 127.0.0.1:10000 +**+ || +**+ 0.0.0.0:22 ssh server    |
  |                 |  ||   |                          |    ||    |                          |
  +-----------------+  ||   +--------------------------+    ||    +--------------------------+

      My Notebook                  Public Server                         Private Server
       localhost                IP address : A.B.C.D                  ( private IP address )
