Basic understanding about Border Gateway Protocol (BGP)
We really want to show you why we need BGP first but it is very difficult to explain without understanding a bit about BGP. So we will learn some basic knowledge about BGP first. First we need to understand about the different between Interior Gateway Protocol and Exterior Gateway Protocol. The difference between them is shown below: – Interior Gateway Protocol (IGP) : A routing protocol operating within an Autonomous System (AS) like OSPF, EIGRP… Usually routers running IGP are under the same administration (of a company, corporation, individual) – Exterior Gateway Protocol (EGP) : A routing protocol operating between different AS. BGP is the only EGP used nowadays In the topology above R1, R2 and R3 should run an IGP to communicate with each other because they are in the same AS. But to connect with other routers in another AS (like a different ISP), R1 and R3 must use an EGP. With BGP, the term autonomous system (AS) refers to a network that oper...