lookup and forwarding (classifica- tion) among these four topics-that is certainly the CIDR approach. In order to cluster or aggregate addresses, a hierarchical notation had to be introduced. In response to this demand, CIDR launched the concept of a prefix. A prefix is a variable-length field that can be anywhere from 0 to 32 bits long. Supernets are implied through which a common access is subsequently provided to unrelated subnets. The principle seemed logical. From Boston, we first needed to go to Chicago and from then on we could go to Minneapolis, Omaha, or Sioux City. The latter three destinations are irrelevant to each other, but they all share something in common-we must first go to Chicago in order to reach any them. This principle was going to be based on address prefixes. Route aggregations would then need to be implemented based on the use of the address prefix. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. CLASSIFICATION PROCESSORS 242 NETWORK PROCESSORS First, addresses were no longer going to be represented as ordinary 4-byte or 32-bit numbers. In the new decimal prefix-based notation, 11.0.0.0 becomes 11/8, 124.54.0.0 becomes 124.54/16, 193.19.3.0 becomes 193.19.3/24, and SO on. Second, the routes needed to be represented in aggregate form to save space in the exploding routing tables. Consider the last example-193.19.3/24. If this an aggregate route, it means that the first 24 bits are the prefix and the remaining 8 bits of any 32-bit address under its hierarchy should be treated as wildcard characters. In our city example, if Minneapolis is 157.9.0/23, Sioux City is 157.9.2/24, and Omaha is 157.9.3/24, we could aggregate them in our routing table as 157.9.0/22 with a new 22-bit prefix that serves all of them. Another router away from us, say, in Chicago, would have to worry about the gran- ularity of the network concerned