BGP stands for Border Gateway Protocol. It can be defined as a standardized exterior gateway protocol which is developed to interchange routing information and reachability information between various autonomous systems (AS) on the Internet. It is classified as a path vector protocol as well as a distance-vector routing protocol.
There are two types of BGP and they are as follows −
Internal BGP − Internal BGP (IBGP) is a BGP connection between BGP speakers in the same AS.
External BGP − External BGP (EBGP) is a BGP connection between BGP speakers in different AS’s.
There are four message types of BGP which are explained below −
Open Message − This is a message that is sent to establish the session after the different autonomous system successfully makes the connection. This message contains the information related to the autonomous system like the version of BGP using, Hold time, BGP identifier (IP address), AS number and some optional parameters.
Update Message − This message is sent after the session has been established successfully. This is used to share the routing information. This type of message contains information on routers that are feasible to access, routers that are not feasible to access and the path attributes.
KeepAlive − This is another message that helps us to be sure that the neighbour router is still up. This message is generally sent before the update message is sent. The neighbour will reset the hold time as soon as it receives the KeepAlive message.
Notification − This is another kind of message sent when some error occurs. It contains error code, specific error sub code and reason for error.
BGP has an advantage as it gives us much more control over what routes we advertise and over what advertisements we accept from our neighbours.
We need it for exchanging routing and reachability information among autonomous systems on the Internet.
It gives control over ours and our neighbour’s route selection. Hence it is the routing protocol for the Internet.
Also, BGP is the most popular exterior gateway protocol. It is more flexible and scalable than Open Shortest Path First (OSPF). Moreover, it puts emphasis on determining the best path.
It provides Internet service advantages as running BGP in our network is almost a must. Multiprotocol Label Switching (MPLS) based Layer 3 VPN services uses BGP as the underlying routing protocol. It increases network stability.
It includes automatic response to sop worms and Denial-of-Service (DoS) attacks. It offers large-scale Quality-of-Service (QOS) and provides scalability.