bgp-4, the classful internet killer...

rfc4271...

BGP-4 provides a set of mechanisms for supporting Classless Inter-
   Domain Routing (CIDR).  These mechanisms include support for
   advertising a set of destinations as an IP prefix, and eliminating
   the concept of network "class" within BGP.  BGP-4 also introduces
   mechanisms that allow aggregation of routes, including aggregation of
   AS paths.

   This document obsoletes RFC 1771.

if rfc's scare you, there is this, however the first page is literally lifted from the rfc...

http://www.bgp4.as/


a fellow network guy i know scoffed at the idea of reading rfc's, as if it was some sort of highbrow pursuit, or a networking holier than thou kind of thing... to that i shake my head in bewilderment and cry bullshit... this is the path we have chosen; rfc's are the trail markers... get used to it... they don't have the pretty pictures, they don't hold your hand, the language can oftentimes seem shakespearian... the texts you read from the publishers  are based  on the rfc's, for God's sake... rfc's are the source... everything else is regurge... 

read em and let the other guy weep...

and don't skip the acknowledgements... they are generally a who's who of network pioneers... radia perlman, russ white, john moy, vint cerf, et al... if these names mean nothing to you, you are in the wrong line of work...

The primary function of a BGP speaking system is to exchange network
   reachability information with other BGP systems.  This network
   reachability information includes information on the list of
   Autonomous Systems (ASes) that reachability information traverses.

 a BGP speaker advertises to its peers only those routes that it uses itself

 Routing information exchanged via BGP supports only the destination-
   based forwarding paradigm, which assumes that a router forwards a
   packet based solely on the destination address carried in the IP
   header of the packet.  This, in turn, reflects the set of policy
   decisions that can (and cannot) be enforced using BGP.

 The
   classic definition of an Autonomous System is a set of routers under
   a single technical administration, using an interior gateway protocol
   (IGP) and common metrics to determine how to route packets within the
   AS, and using an inter-AS routing protocol to determine how to route
   packets to other ASes.

  BGP uses TCP [RFC793] as its transport protocol.  This eliminates the
   need to implement explicit update fragmentation, retransmission,
   acknowledgement, and sequencing.  BGP listens on TCP port 179.  The
   error notification mechanism used in BGP assumes that TCP supports a
   "graceful" close (i.e., that all outstanding data will be delivered
   before the connection is closed).

   A TCP connection is formed between two systems.  They exchange
   messages to open and confirm the connection parameters.

  KEEPALIVE messages may be sent periodically to ensure that the
   connection is live.  NOTIFICATION messages are sent in response to
   errors or special conditions.  If a connection encounters an error
   condition, a NOTIFICATION message is sent and the connection is
   closed.