Interior and Exterior Gateway Protocols (IGP and EGP)
Interior gateway protocols route traffic within one network, while exterior gateway protocols route traffic between networks.
What is Interior and Exterior Gateway Protocols (IGP and EGP)?
Common IGPs are OSPF, IS-IS and EIGRP; they find the best path inside an autonomous system. BGP is the exterior gateway protocol used on the internet. ("EGP" was also the name of BGP's obsolete predecessor.)