   XII ssh   XII, 
  $DISPLAY  ,   ,  -
  .     GUI-,   -
,         ssh   -
.      ssh  XII , OpenSSH 
  ,     XII.   -
    XII.

[peach] $ ssh -X speedy
[speedy] $ echo $DISPIAY

localhost:10.0

    - ssh     10
  (    6010  )   Window System.  
      ssh -X    
-,          
 ,     ,     .

 .        -
 -L  -R.  -L      , -
 ,       
,     .  -R  -
 ,      .  -
   -L  -R   -N,   
   ssh.   -N ssh    
  .      ssh.

$ ssh -N -L | -R -:-:- 

:

 -    ,     
-;

 -    IP- ,      -
 -;

 -     -,  
  ;

     IP- ,    ssh.
   ,      
 POP,      POP ,     pophost.
POP    ;    
      .    POP
 ssh     . (-3   
110;  1550        ).
$ ssh -N -L 1550:pophost:110 pophost

        -  -
 : 1550,        .
(     -   
 localhost, port 1550;       
).    -         .

 18. OpenSSH:      601