64 lines
4.3 KiB
HTML
64 lines
4.3 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Classless Inter-Domain Routing" />
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<meta name="abstract" content="Classless Inter-Domain Routing can reduce the size of your routing tables and make more IP addresses available within your business." />
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<meta name="description" content="Classless Inter-Domain Routing can reduce the size of your routing tables and make more IP addresses available within your business." />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Classless Inter-Domain Routing</title>
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</head>
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<body id="rzajwcidr"><a name="rzajwcidr"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Classless Inter-Domain Routing</h1>
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<div><p>Classless Inter-Domain Routing can reduce the size of your routing
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tables and make more IP addresses available within your business.</p>
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<p>Classless Inter-Domain Routing (CIDR or supernetting) is a way to combine
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several class-C address ranges into a single network or route. This method
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of routing adds class-C Internet Protocol (IP) addresses. These addresses
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are given out by Internet service providers (ISPs) for use by
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their customers. CIDR addresses can reduce the size of your routing tables
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and make more IP addresses available within your business.</p>
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<p>In the past, you were required to enter a subnet mask that was equal to
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or greater than the mask required for the network class. For class-C addresses,
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this meant a subnet of 255.255.255.0 was the largest (253 host) that could
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be specified. To conserve IP addresses, when companies needed more than 253
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hosts in a network, the Internet was issuing several class-C addresses. This
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made the configuration of routes and other things difficult.</p>
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<p>Now, CIDR allows these contiguous class-C addresses to be combined into
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a single network address range by using the subnet mask. For example, if you
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are giving out four class-C network addresses (208.222.148.0, 208.222.149.0,
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208.222.150.0, and 208.222.151.0 with a subnet mask of 255.255.255.0), you
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can ask your ISP to make them a supernet by using the subnet mask 255.255.252.0.
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This mask combines the four networks into one for routing purposes. CIDR is
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beneficial because it reduces the number of assigned but unnecessary IP addresses.</p>
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<br /><img src="rzajw519.gif" alt="CIDR" /><br /><p>In this example, the router is set up to send one RIP message with the
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network address 210.1.0.0 and subnet mask 255.255.240.0. This tells your systems
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to receive the RIP messages for networks 210.1.0.0 through 210.1.15.0 through
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this router. This sends one message rather than the 16 that it would take
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to convey the same information if CIDR were not available.</p>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzajwrcb.htm" title="Routing deals with what path the network traffic follows from its source to its destination and how that path is connected.">Routing connectivity methods</a></div>
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</div>
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</div>
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</body>
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</html>
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