Handbook of Local Area Networks, 1998 Edition:LAN Interconnectivity Basics Click Here! Search the site:   ITLibrary ITKnowledge EXPERT SEARCH Programming Languages Databases Security Web Services Network Services Middleware Components Operating Systems User Interfaces Groupware & Collaboration Content Management Productivity Applications Hardware Fun & Games EarthWeb sites Crossnodes Datamation Developer.com DICE EarthWeb.com EarthWeb Direct ERP Hub Gamelan GoCertify.com HTMLGoodies Intranet Journal IT Knowledge IT Library JavaGoodies JARS JavaScripts.com open source IT RoadCoders Y2K Info Previous Table of Contents Next USING NONUNIQUE ADDRESSES In the past, acquiring a globally unique IP address and connecting to the Internet was sufficient to gain access to the Internet routing system. Gaining access to the Internet routing system was viewed as synonymous with being on the Internet. Growth of the Internet, and the need to contain the routing overhead in the Internet routing system makes unique addresses no longer sufficient to gain access to the Internet routing system, and therefore no longer sufficient to be on the Internet. To gain access to the Internet routing system (and therefore be on the Internet) requires addresses to be not just unique, but to reflect the underlying network topology, to make addresses suitable for the hierarchical aggregation. The globally unique address by itself does not necessarily guarantee global connectivity. Individual network service providers may place restrictions on what addresses they will or will not route based on operational limitations. At the same time, development of various types of mediating gateways (e.g., application layer gateways, Network Address Translators or NATs), shows that to be on the Internet is no longer synonymous with gaining access to the Internet routing system. To the contrary, such a development shows that to be on the Internet could be accomplished without gaining access to the Internet routing system, and therefore without having globally unique IP addresses. Although many enterprises have IP layer connectivity to the Internet, this connectivity is usually extended into such enterprises to only a very limited number of hosts (if any). Most of the hosts within such enterprises connect to the Internet only through some form of a mediating gateway. If an enterprise is connected to the Internet by some form of a mediating gateway, the enterprise effectively creates its own, private Internet. Because routing in the private Internet is completely segregated from the Internet routing, address allocation within the private Internet is no longer subject to the address allocation procedures for the Internet. The Internet Addressing and Naming Authority (IANA) allocated a block of IP addresses for use in such private Internets. Any enterprise that has a private Internet could use these addresses for allocation to the hosts attached to such Internet. Use of mediating gateways in conjunction with addresses allocated for private Internets significantly simplifies address allocation procedure, as it eliminates the need to acquire addresses out of some Internet Registry. Use of addresses allocated for private Internets also simplify design of an addressing plan for an enterprise, as it provides the enterprise with the amount of address space that is significantly larger than the enterprise would be able to acquire out of any Internet Registry. Finally, the use of addresses allocated for private Internets further defers IP address space exhaustion by allowing multiple enterprises to reuse the same address space. Introduction of address reuse in combination with mediating gateways enables the Internet to grow well beyond the limits of the IP address space. In fact, it could be argued that the use of addresses allocated for private Internets in conjunction with mediating gateways could solve the IP address space exhaustion problem. SUMMARY IP addressing and routing have been in constant evolution since IP was first specified. Some of the addressing and routing principles have been deprecated, some of the principles have been preserved, and new principles have been introduced. The introduction of CIDR was motivated by the following three problems: potential exhaustion of Class B network numbers, the need to improve scalability of the Internet routing system, and potential exhaustion of the IPv4 address space. CIDR solved the first problem by eliminating the notion of network numbers, and allowing to use variable-length address prefixes for address allocation. CIDR solved the second problem by introducing additional level of address information aggregation at the level of providers, and by allowing aggregation of addressing information into variable-length address prefixes. Finally, CIDR defers (but does not solve) the third problem by enabling a better match between the amount of address space required and the amount of address space allocated, and by allowing to use any part of the IP address space (including the part formerly known as Class A network numbers) for the address allocation. Gaining access to the Internet routing system is a way of being on the Internet. Doing this, however, requires globally unique and routable addresses. Use of mediating gateways allows to be on the Internet without requiring addresses to be globally unique and routable. Globally unique addresses are no longer either necessary, or sufficient to be on the Internet. Use of nonunique addresses (in conjunction with mediating gateways) allows to grow the Internet beyond the limits of IP address space, and preserves the current IP protocol. Current CIDR-based Internet routing and addressing is an evolutionary step that extends the use of hierarchical routing to maintain a routable global Internet, while preserving its ability to grow. Previous Table of Contents Next Use of this site is subject certain Terms & Conditions. Copyright (c) 1996-1999 EarthWeb, Inc.. All rights reserved. Reproduction in whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Please read our privacy policy for details.