 

   (  ), 
  (match extensions),   , -
 ,      .    -
   ,        -
 . ,   ,   
   ,   ,  ,   . -
    :   .

  

    .    ( 
)     protocol (. ).   -
    .     -h, 
 ,      . , -
 iptables -p tcp -h       TCP.

 protocol [! ] , -.     , 
   .      
   /etc/protocols, , tcp, udp  icmp (. ).
 all  0 ()     tcp, udp  icmp, 
     .
    TCP    
TCP,    22 ( ssh):

protocol tcp source-port 22

    , ,  iptables 
    ssh.     ssh, -
 iptables    /etc/services,     22.

# iptables --protocol tcp --source-port ssh -jump DROP

      ;      -
    -h.

TCP

 --destination-port [!] [ ] [: ] . dport.    
   (. /etc/services).     -
 , -.     0  ,  :   
   65535.

 source-port [!] [] [: ]. sport.     
  (. /etc/services).      -
, :     0  ,  :      
65535.

 [!] syn.      SYN   -
   FIN.       tcp-
flags SYN,RST,ACK SYN.

766  V.     