 2.   TCP/IP____________________________115

        EGP.
 BGP     IGP -
  EGP,    EGP   
 .  incomplete   
,       -  .

  (path).  AS.    AS  
  .

   (next hop).   IP-, 
        ,
    .

  (unreachable). ,  - 
   .

     AS (inter-AS metric). -
  -  BGP  
      ,  
  AS.      -
,       AS 
,       
,     AS.

"1  " " (keepalive message).  
  -    ,  -
   BGP.

    (error message).    
,          -
 ,      .  -
    (error code),   (error
subcode)    (error data).

Marker (16 ).  .   ,  -
    (,   -
 ).       
     BGP-.

Length (16 ).   .      -
  ,    .

Type (8 ).    (Open, Notification, Update, Keepalive,
Errors).

   BGP   ,  -
 .

     BGP    RFC-1105,
RFC-1163, RFC-1164, RFC-1267, RFC-1364, RFC-1403, RFC-1654, RFC-1771,
RFC-1772.