    ,  iptables   ,  0 
1     /etc/sysctl.conf,     IP-
:

net.ipv4.ip forward = 

    
  Internet

   ,     -
       Internet,    IP,
 SNAT (NAT  ).  IP    
    ,    ,  -
,        .   
,   .      
  ,   ,   -
 ( Internet).       , 
   .

      ,     -
  IP-    IP-  Internet.
     ,  -
 ,     Internet,    ,   Internet
 ,          
10.255.255.255.  ,       Internet -
 ,        
Internet     10.255.255.255.    
           
 .     
iptables,         .
       FORWARD  FILTER (
) (-A FORWARD):

# iptables -A FORWARD -i ethO - ethi -m state state ESTABLISHED,RELATED
-j ACCEPT

   ,   :

1.   ethO (  Internet): -i ethO.

2.    ethi (  LAN): - ethi.

3.     ,   
: --state ESTABLISHED, RELATED.

  (-j ACCEPT) ,    .
     /. -
       FORWARD.   Internet,
   ,    .

       FORWARD  FILTER:

# iptables -A FORWARD -i ethi - ethO -j ACCEPT

 25. iptables:   773