BGP ( Border gateway Protocol )

             The Border Gateway Protocol is the routing protocol of the Internet. Actually internet is comprised of Many Autonomous Systems ( AS ).BGP’s task is to maintain lists of efficient paths between ASes.


             A set of computers and routers under a single administration, such as a university or company network, is known as an autonomous system (AS)

How BGP Works : 

      

             BGP Works by Establishing a Network Connection with another BGP Router using TCP 
protocol on port no 179. Once the connection is established between two routers then those routers are said to be BGP Neighbours. 

            After BGP peering finishes then two routers will exchange their Routing Information eachother and each router will buid up their forwarding information base based on Routing Information base and local policy rules.

            Each AS will have many routers for internal communication, and one or more routers for communications outside the local network.Internal routers use internal BGP (iBGP) to communicate with each other, and external routers use external BGP (eBGP). (iBGP and eBGP are the same protocol, but use different routing rules; iBGP does not advertise third-party, outside routes.)

The BGP standard defines four message types:
•  OPEN
•  UPDATE
•  NOTIFICATION
•  KEEPALIVE.

OPEN Message Format :

Field	Length (bytes)
BGP version	1
Autonomous system number	2
Hold time	2
BGP identifier (IP address)	4
Optional parameters length	1
Optional parameters	variable: 0..255 bytes

UPDATE Message Format

Field	Length (bytes)
Withdrawn routes length	2
Withdrawn routes	variable
Path attributes length	2
Path attributes	variable
Network layer reachability information	variable

Dear Readers kindly post your valuable suggestions and comments below which will initiate me to make this blog with more information.