Route Propagation
	Idea: Impose a second hierarchy on the network that limits what routers talk to each other. (The first hierarchy is the address hierarchy that governs how packets are forwarded.) n Autonomous System (AS) – corresponds to an administrative domain – examples: University, company, backbone network – assign each AS a 16-bit number n Two-level route propagation hierarchy – interior gateway protocol (each AS selects its own) – exterior gateway protocol (Internet-wide standard)