 --tcp-flags [!]  .    TCP,  -
.   SYN, , FIN, RST, URG, PSH, ALL, NONE.  
     ,     -
  ,  ,    
  . ,    ,   -
.

 tcp-option [!] .   TCP     ().

UDP

       /   -
,      "TCP".

1

 ICMP (. )   .

 --icmp-type [! ] . ,    ICMP-  .
     ICMP    ,  

# iptables -p icmp -h

  

      ,   -
        -  --match. -
     ;     
     state.



    ,   
(.  ""    ).

 --state .  ,    
        :

ESTABLISHED     ,    -
       .
INVALID          .
NEW            ,   SYN.
RELATED      ,  ,  -
 ESTABLISHED. ,   FTP,  
    FTP. (  -
 FTP   ip_conntrack_ftp.)

   ,   
        :

# iptables --match state --state INVALID,NEW -jump DROP

 25. iptables:   767