192 lines
12 KiB
HTML
192 lines
12 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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<meta name="DC.Type" content="reference" />
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<meta name="DC.Title" content="Example: DHCP and multihoming" />
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<meta name="abstract" content="You can learn how to set up the iSeries server as a DHCP server for a LAN that is connected to the Internet by an Internet router." />
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<meta name="description" content="You can learn how to set up the iSeries server as a DHCP server for a LAN that is connected to the Internet by an Internet router." />
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<meta name="DC.Relation" scheme="URI" content="rzakgexampleparent.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzakgscenario1.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzakgproblemnoip.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 2004, 2006" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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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>Example: DHCP and multihoming</title>
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</head>
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<body id="rzakgscenario3"><a name="rzakgscenario3"><!-- --></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">Example: DHCP and multihoming</h1>
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<div><p>You can learn how to set up the iSeries™ server as a DHCP server for a
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LAN that is connected to the Internet by an Internet router.</p>
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<div class="section"><p>This example is much like the first example, Simple DHCP subnet.
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In this example, the data entry clients are only communicating amongst themselves
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and the iSeries server.
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They obtain their IP information dynamically from the iSeries' DHCP server.</p>
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<p>However,
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a new version of their data entry application requires that the network communicates
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with the Internet, and the company decided to provide Internet access through
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an Internet router as shown in Figure 4-1. In addition to the router, the
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administrator also added another interface with an IP address to communicate
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with the Internet. When multiple IP addresses are assigned to the same adapter,
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the iSeries server
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is multihoming.</p>
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<div class="fignone"><span class="figcap">Figure 1. Using DHCP with multiple IP addresses assigned
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to the same adapter</span><br /><img src="rzakg503.gif" alt="Using DHCP with multiple IP addresses assigned to the same adapter." /><br /></div>
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<div class="note"><span class="notetitle">Note:</span> Although this is a feasible way to connect your network to the
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Internet, it is not the most secure. It suits the purposes of this DHCP example,
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but you should consider the security implications when you configure your
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own DHCP server.</div>
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<p>The DHCP setup must take into account that the iSeries server
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is known by two different IP addresses. To understand how to set up DHCP correctly
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for this scenario, it is helpful to understand what happens when a client
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sends out a DHCP DISCOVER packet.</p>
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<p>When a client sends out a DHCP DISCOVER
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packet, it is broadcast on the ring. Therefore, iSeries server cannot determine
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which IP address the packet was intended for. If this packet is marked with
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the 10.1.1.1 interface IP (the one used for DHCP), your clients receive their
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IP information as expected. But it is possible that the packet can actually
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get marked with the 192.168.1.1 address (the one connected to the Internet).
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If the packet is received on the 192.168.1.1 interface, your data entry client
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does not receive any IP information.</p>
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<p>To set up DHCP in this situation,
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you need to not only create the data entry DHCP subnet, but also one for the
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Internet network. The Internet policy consists of a subnet with no available
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addresses. The easiest way to do this is to define the subnet with at least
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one IP address (like 192.168.1.1), then exclude that same IP address. With
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the two subnets defined, you now combine the two (or more) subnets into a
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subnet group. If the DISCOVER packet gets marked with the 192.168.1.1 interface,
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the data entry subnet will still issue valid IP information.</p>
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<p>To make
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this scenario work, the policy for the Data Entry subnet must pass its clients
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their router address for access to the Internet. In this case, the router
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address is the iSeries interface
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of 10.1.1.1. You must also set IP Datagram forwarding to 'on' for the two
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interfaces to route packets to each other. This example uses reserved IP addresses
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to represent both internal and external IP addresses. If your network matches
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this scenario, you also need to use NAT for your Data Entry clients to communicate
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with the Internet.</p>
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<p>Using subnet groups to eliminate this marking problem
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is not only limited to multihoming examples. Any time multiple interfaces
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connect to the same network, you can encounter the same problem. The following
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figure illustrates how the iSeries server can have two physical connections
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to the data entry network. This network configuration requires a similar DHCP
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group policy as the multihoming setup, because DHCP DISCOVER packets can conceivably
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be answered by the 192.168.1.1 interface.</p>
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<div class="fignone"><span class="figcap">Figure 2. Using DHCP with multiple
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interfaces connected to the same network</span><br /><img src="rzakg504.gif" alt="Using DHCP with multiple interfaces connected to the same network." /><br /></div>
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</div>
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<div class="section"><h4 class="sectiontitle">Planning the DHCP setup for multihoming</h4>
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" width="100%" frame="border" border="1" rules="all"><caption>Table 1. Global configuration options (applies to all clients served by the
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DHCP server)</caption><thead align="left"><tr><th valign="top" width="42.2680412371134%" id="d0e75">Object</th>
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<th valign="top" width="57.73195876288659%" id="d0e77">Value</th>
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</tr>
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</thead>
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<tbody><tr><td valign="top" width="42.2680412371134%" headers="d0e75 ">Is the server performing DNS updates?</td>
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<td valign="top" width="57.73195876288659%" headers="d0e77 ">No</td>
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</tr>
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<tr><td valign="top" width="42.2680412371134%" headers="d0e75 ">Is the server supporting BOOTP clients?</td>
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<td valign="top" width="57.73195876288659%" headers="d0e77 ">No</td>
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</tr>
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</tbody>
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</table>
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</div>
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" width="100%" frame="border" border="1" rules="all"><caption>Table 2. Subnet for Data Entry clients</caption><thead align="left"><tr><th colspan="2" valign="top" id="d0e99">Object</th>
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<th valign="top" width="58.18815331010453%" id="d0e101">Value</th>
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</tr>
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</thead>
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<tbody><tr><td colspan="2" valign="top" headers="d0e99 ">Subnet name</td>
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<td valign="top" width="58.18815331010453%" headers="d0e101 ">Data Entry</td>
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</tr>
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<tr><td colspan="2" valign="top" headers="d0e99 ">Addresses to manage</td>
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<td valign="top" width="58.18815331010453%" headers="d0e101 ">10.1.1.2 - 10.1.1.150</td>
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</tr>
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<tr><td colspan="2" valign="top" headers="d0e99 ">Lease time</td>
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<td valign="top" width="58.18815331010453%" headers="d0e101 ">24 hours (default)</td>
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</tr>
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<tr><td rowspan="4" valign="top" width="13.937282229965156%" headers="d0e99 ">Configuration options </td>
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<td valign="top" width="27.874564459930312%" headers="d0e99 ">option 1: Subnet mask </td>
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<td valign="top" width="58.18815331010453%" headers="d0e101 ">255.255.255.0 </td>
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</tr>
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<tr><td valign="top" width="27.874564459930312%" headers="d0e99 ">option 3: Router </td>
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<td valign="top" width="58.18815331010453%" headers="d0e101 ">10.1.1.1 </td>
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</tr>
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<tr><td valign="top" width="27.874564459930312%" headers="d0e99 ">option 6: Domain name server </td>
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<td valign="top" width="58.18815331010453%" headers="d0e101 ">10.1.1.1 </td>
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</tr>
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<tr><td valign="top" width="27.874564459930312%" headers="d0e99 ">option 15: Domain name</td>
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<td valign="top" width="58.18815331010453%" headers="d0e101 ">mycompany.com </td>
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</tr>
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<tr><td colspan="2" valign="top" headers="d0e99 ">Subnet addresses not assigned by server</td>
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<td valign="top" width="58.18815331010453%" headers="d0e101 ">10.1.1.1 (Router, DNS server)</td>
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</tr>
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</tbody>
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</table>
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</div>
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" width="100%" frame="border" border="1" rules="all"><caption>Table 3. Subnet for Internet clients (empty Subnet)</caption><thead align="left"><tr><th valign="top" width="41.62436548223351%" id="d0e154">Object</th>
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<th valign="top" width="58.37563451776649%" id="d0e156">Value</th>
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</tr>
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</thead>
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<tbody><tr><td valign="top" width="41.62436548223351%" headers="d0e154 ">Subnet name</td>
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<td valign="top" width="58.37563451776649%" headers="d0e156 ">Internet</td>
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</tr>
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<tr><td valign="top" width="41.62436548223351%" headers="d0e154 ">Addresses to manage</td>
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<td valign="top" width="58.37563451776649%" headers="d0e156 ">192.168.1.1 - 192.168.1.1</td>
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</tr>
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<tr><td valign="top" width="41.62436548223351%" headers="d0e154 ">Subnet addresses not assigned by server</td>
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<td valign="top" width="58.37563451776649%" headers="d0e156 ">192.168.1.1 (All IP addresses available)</td>
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</tr>
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</tbody>
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</table>
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</div>
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<div class="tablenoborder"><table cellpadding="4" cellspacing="0" summary="" width="100%" frame="border" border="1" rules="all"><caption>Table 4. Subnet group for all incoming DISCOVER
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packets</caption><thead align="left"><tr><th valign="top" width="41.62436548223351%" id="d0e182">Object</th>
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<th valign="top" width="58.37563451776649%" id="d0e184">Value</th>
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</tr>
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</thead>
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<tbody><tr><td valign="top" width="41.62436548223351%" headers="d0e182 ">Subnet Group Name</td>
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<td valign="top" width="58.37563451776649%" headers="d0e184 ">Multihomed</td>
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</tr>
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<tr><td valign="top" width="41.62436548223351%" headers="d0e182 ">Subnets included in group</td>
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<td valign="top" width="58.37563451776649%" headers="d0e184 "><p>Subnet Internet<br />
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Subnet DataEntry</p>
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</td>
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</tr>
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</tbody>
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</table>
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</div>
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</div>
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<div class="section"><h4 class="sectiontitle">Other setup</h4><ul><li>Set IP Datagram forwarding to 'on' for the two interfaces</li>
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<li>Set up NAT for the Data Entry clients</li>
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</ul>
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</div>
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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="rzakgexampleparent.htm" title="By reviewing diagrams and examples of how different networks are set up, you can determine which is the best choice for your installation.">DHCP examples</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="rzakgproblemnoip.htm" title="Problems might occur if the clients cannot receive an IP address or the configuration information. An IP address is leased to a client through a four-step process between the client and the DHCP server.">Problem: Clients are not receiving an IP address or their configuration information</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="rzakgscenario1.htm" title="You can learn how to set up the iSeries server as a DHCP server in a simple LAN with four PC clients and a LAN-based printer.">Example: Simple DHCP subnet</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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