    : Filter, NAT  Mangle.     
 ,   .    Filter 
 ,   .

Filter.  .     ,  
(DROP)   (ACCEPT)     ,    -
.    INPUT (), FORWARD ()  OUTPUT
().        .

NAT.    .     , -
  ,       
   .    PREROUTING (-
 ), OUTPUT ()  POSTROUTING ( -
).     DNAT, SNAT  MASQUERADE.

 DNAT (Destination NAT  NAT )  IP-  -
    ,       .
    .  
     Internet,  
      (.  " 
     Internet"    ).

 SNAT (Source NAT  NAT )  IP-   -
   ,        -
 IP-, ,    . -
    .   -
   ,    
 .       LAN  -
   LAN     IP-  
  . .   "MASQUERADE".

 MASQUERADE ()   SNAT  ,   IP-
    ,      -
 IP-, ,  DHCP ( "DHCP" -
 11).  MASQUERADE   ,  SNAT.

Mangle.        TOS (Type of
Service   ), TTL (Time To Live   )  MARK. -
   PREROUTING  OUTPUT ( ) 
OUTPUT ().

 .          ,  -
     ,      -
 .        
PREROUTING,        (. 25.2).
       .   -
  ,      INPUT,   
  (,      )  -
.        (  -
 ),    ,      -
  .

        OUTPUT 
POSTROUTING,           .

758                            V.     