Bgp

Basics

• BGP - Border Gateway Protocol
• Consists of large number Autonomous Systems - Routers controlled by one entity
• Each AS is allocated a unique ASN by IANA. They are 16 bits in length & have value between 0 - 65535. 6451-65534 are private
• BGP operates over tcp/179
• AS need to be peered manually. Each individual AS exchange routing and topology information with all other peered AS
• BGP is a path-vector protocol. i.e. It exchanges best path to a destination between peers. The path is called as ASPPATH.
• Only best path is exchanged.
• BGP does not consider link speed or condition. It only focuses on path
• iBGP focuses on routining within an AS while eBGP focuses on routing between AS
• Shorter ASPATH means short path
• ASPATH Prepending can be used in order to prioritize faster paths. This makes the slower routes to have longer ASPATHs, thus slower paths get deprioritized