OSPF and IS-IS: Choosing an IGP for Large-Scale Networks

9.1. Routing Protocol Vulnerabilities

As you are sure to know, routing protocols can be classified as either interior or exterior gateway protocols (IGPs or EGPs). For routing IP, Border Gateway Protocol (BGP) is the only EGP currently in widespread use; all other commonly used IP routing protocols—including OSPF and IS-IS—are IGPs. Although the mission of both types of routing protocols is to exchange route information, how they go about the information exchange differs significantly. Like any device outside of your administrative domain, external routers must be considered untrusted. BGP is designed to work in conjunction with complex routing policies so that you have detailed control over what information is shared and accepted from external ...