Border Gateway Protocol

Overview

• Autonomous System (AS) - self managing network
• BGP comprises of ASs and viewed as black box
• Autonomous System Number(ASN) are unique and allocated by IANA (0-65535), 64512-65534 are private
• Distributed and Reliable and operates over tcp/179
• Peering between two AS is not automatic
  • peering is manually configured
• iBGP = Internal BGP - Routing within an AS
• eBGP = ExternalBGP - Routign between AS's

BGP path traversal

BGP is a path-vector protocol

• exchanges the best path to a destination between peers
• the path is called ASPATH
• does not consider link speed or condition while calculating and advertising shortest path to its peers
• Prepending same ASN no. to the ASPATH can be used to artifically make a path longer making the other path preferred (if needed).