Exterior Gateway Protocols (EGP): Used for routing between autonomous systems. It is also referred to as inter-AS routing. Service providers and large companies may interconnect using an EGP. The Border Gateway Protocol (BGP) is the only currently viable EGP and is the official routing protocol used by the Internet. Because BGP is the only EGP available, the term EGP is rarely used; instead, most engineers simply refer to BGP. https://www.ciscopress.com/articles/article.asp?p=2180210&seqNum=7