Internet Exterior Routing Protocol Development: Problems, Issues, and Misconceptions

50 his interim solution in no way constrains the selection of the next generation addressing and routing technology.” — RFC 1367, October 1992 [1] In 1977, Kleinrock and Kamoun [2] published a detailed discussion of hierarchical routing in large internetworks. In their landmark paper, “Hierarchical Routing for Large Networks,” they discussed the problems associated with scalability and the length of the route forwarding table in large packet-switched networks. They concluded that hierarchical routing was a requirement for very large networks. Routing tables require less information for destination networks far from the source relative to hop count or another nearness metric. Detailed routing information, one entry per destination, is required for near nodes. The construction of logical sets in the routing hierarchy is not related to geographical distances. Instead, administrative clustering of routing domains becomes the technical basis for designing large scalable internetworks. Problems and issues with scalability in packet-switched networks were well documented prior to 1982, the publication date of Rosen’s Internet Request for Comment, “Exterior Gateway Protocol” (EGP) [3]. In this publication, Rosen discussed hierarchical routing and the limitations of EGP clearly and concisely, cautioning the reader that EGP did not “constitute a network routing algorithm.” Unable to predict the explosive growth of the Internet, the National Science Foundation (NSF), Internet Engineering Task Force (IETF), Internet Activities Board (IAB), Internet Protocol (IP) service providers, and router vendors embarked on a development track redesigning EGP in favor of the Border Gateway Protocol (BGP). Policy-based routing dominated requirements for global scalability in large packet switched networks. Further inspection confirms that the early IP exterior routing protocol development track by Internet developers and router vendors was dominated by concerns about policy-based routing [4–6]. It was not until 1992 that the engineering focus in the IETF apparently began to shift from policy-based routing to global network scalability [7–9]. A short synopsis of IP exterior routing protocol development is presented in the next section, highlighting EGP, BGP, and policy-based routing in the Internet. The section after that introduces the paradigm shift from a concentration on policy-based routing to an emphasis on global IP scalability. The focus then returns to the BGP-3→BGP-4 paradigm shift associated with classless interdomain routing (CIDR). Important quotations in the Internet Requests for Comments (RFCs) are highlighted as the discussion develops. The fifth section presents a generic global hierarchical routing model which is introduced as a basis for discussion relative to both provider and geographic IP address allocation paradigms. The discussion highlights important statements in the Internet RFCs related to the topic, and the developed model demonstrates weaknesses in provider-based address space allocation. The sidebar shows a brief summary of historical call routing in the pre-1984 Bell System and the present telephony hierarchical model. At the end of the article, the presented models, relative analysis, and business issues provide a foundation for discussing the problems with a hierarchical routing model for the Internet based on the current implementation of providerbased IP address space aggregation.