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BGP Introduction

BGP – Border Gateway Protocol is the backbone of internet. It is a type of Exterior Gateway protocol and successor of EGP protocol. BGP is generally used for Inter Domain (AD) routing such as between two ISP for exchanging routing information. Below are the some key points wrt BGP :-
1. It is a type of EGP while OSPF, IS-IS, EIGRP are type of IGP.
2. It is a slow protocol i.e BGP is meant for scale not speed so BGP is slow to converge in comparison of IGPs.
3. BGP relies on TCP protocol and its TCP port no is 179.
4. There has to has a TCP connection before BGP forms Neighbourship.
5. There are no dynamic neighbourship, only static neighbourships are there.
6. Hellos are known as Keepalive in BGP.
7. It is a Path Vector protocol.
8. It carries not only prefixes but also many path attribute along with them.
9. It is of Two Types – iBGP and EBGP.
10. iBGP is used in the AD (Domain only) while eBGP is used for between Admin Domains.
11. AD(here AD is Admin distance) values of iBGP is 200 and EBGP is 20.
12. It can support different address families such as IPv4/IPv6/Unicast/Mcast.
13. BGP has three tables to maintain :-
 13.a In Table – Routes received from BGP neighbour stored here.
13.b BGP Table – BGP best Routes are stored here.
13.c BGP Out table – Routes advertised to neighbours are stored here.
14. BGP has Acknowledgement for every message.

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