 to IPv4 was quickly used up mainly because the netid boundaries were not flexible. Class addresses would only be offered to large organizations that could justify hundreds of thousands of hosts. Class C was deemed extremely narrow, as many organizations needed addressing for more than 1. Christian Huitema, Routing in the Internet, 2nd ed. (Upper Saddle River, New Jersey: Prentice-Hall, 2000). 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 CLASSIFICATION PROCESSORS 241 Classes of IPv4 addresses Class A Network Class B Network Class C Network Class D Multicast address Class E 11110 Unused FIGURE 13.2 The structure of the original address classes in IPv4. the 256 hosts that the 8 bits allocated for that effect could allow. Since Class B addresses were the least evil of the remaining options for organizations seeking pools of addresses, the prospect that we would run out of useful addresses soon was real. To further compound the problem, the simultaneous explosive growth of the number of routes kept inside forwarding tables created an equally untenable problem. In order to address these parallel problems, the Internet Engineering Task Force (IETF) worked on several issues. In addition to the appearance of more sophisticated routing protocols (such as the Border Gateway Protocol [BGP]), the following interesting developments occurred: Classless Interdomain Routing (CIDR) appeared and boundaries were eliminated between classes with the adoption of hierarchical addressing and routing. Network Address Translation (NAT) schemes were specified and implemented. Dynamically assigned addresses were proposed. IPv6 with addresses that were 128 bits long was invented. As the industry has not yet fully moved over to IPv6, the status quo of modern networks forces us to determine what is of immediate interest for this discussion on 