A comparison of three members of a class of WAN routing protocols called "interior gateway protocols." Each member of the class - RSTP, OSPFv2, and IS-IS - is bound to a different kind of datagram: Ethernet frames, IP packets, and OSI CLNP datagrams respectively. Most companies with large WANs use one of the first two protocols for two purposes: to route around failed redundant links and to automatically find the correct path to a destination address on a large network with many hops. Including RSTP in the comparison is a realistic acknowledgment of the way L2 switching is abused these days. Including OSI in the comparison should reveal some habitually irritating aspects of switched IP networks that are mere accidents of history, and others that are more fundamental. Miles will provide background about how Ethernet switching works, what an IGP is, and what the now mostly-abandoned supposed-future OSI world feels like.