TAILIEUCHUNG - The Complete IS-IS Routing Protocol- Part 3

The Complete IS-IS Routing Protocol- P3: IS-IS has always been my favourite Interior Gateway Protocol. Its elegant simplicity, its well-structured data formats, its flexibility and easy extensibility are all appealing – IS-IS epitomizes link-state routing. Whether for this reason or others, IS-IS is the IGP of choice in some of the world’s largest networks. | 6 1. Introduction Motivation and Historical Background Responding to increasing demand from customers Cisco Systems began shipping NLSP in 1994. Because NLSP and IS-IS are so similar Cisco s engineering department decided to do some internal code housekeeping and merged the base functions of the two protocols in one tree . This rewriting work was the springboard for one of the most respected IGP routing protocol engineers in the world. Cisco Systems hired a software engineer named Dave Katz from Merit the management company of the NSFNet backbone. Merit was in the early 1990s the place where many of the huge talents in Internet history got their routing expertise. Large-scale Deployments Cisco gained a lot of momentum in the early 1990. The company attracted all the key talent in routing protocol and IP expertise and finally got more than a 98 per cent market share in the service provider equipment space. When the first big router orders were placed and the routers deployed for the Web explosion Internet service provider ISP customers started to ask their first questions about scalability. Service providers were interested in a solid quickly converging protocol that could scale to a large topology containing hundreds or even thousands of routers. Cisco s proprietary distance-vector EIGRP was not really a choice because the convergence times and stability problems of distance-vector-based protocols were well known from word-to-mouth in the service provider community. Ironically it was Cisco s recent code rewrite that made IS-IS more stable than the implementations of OSPF available at the time. For a while IS-IS was believed to be as dead as the OSI protocols. However the 1980s mandate of the US government for supporting OSI protocols under the Government OSI Profile GOSIP specification which was still in effect plus recently gained stability made IS-IS the logical choice for any service provider that needed an IGP for a large number of nodes. From about 1995

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