Border Gateway Protocol (BGP) is an exterior gateway protocol used on the internet and ISPs to exchange routing and reachability information. BGP is a layer 4 path vector routing protocol that uses port 179. It is the only EGP that is still in use today. The current BGP version is BGPv4 which was published as RFC 4271 in 2006.

Unlike other IGPs (OSPF, EIGRP, or RIP), BGP has many metrics or attributes in choosing the best path in the network. These attributes are for path manipulation. We will check it one by one as those attributes influence either inbound or outbound traffic.