212 lines
15 KiB
HTML
212 lines
15 KiB
HTML
|
<?xml version="1.0" encoding="UTF-8"?>
|
||
|
|
<!DOCTYPE html
|
||
|
|
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
||
|
|
<html lang="en-us" xml:lang="en-us">
|
||
|
|
<head>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
||
|
|
<meta name="security" content="public" />
|
||
|
|
<meta name="Robots" content="index,follow" />
|
||
|
|
<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))' />
|
||
|
|
<meta name="DC.Type" content="concept" />
|
||
|
|
<meta name="DC.Title" content="Network topology considerations" />
|
||
|
|
<meta name="abstract" content="You can plan for most of the DHCP setup by looking at your network topology, the devices on the network (for example, routers), and how you want to support your clients in DHCP." />
|
||
|
|
<meta name="description" content="You can plan for most of the DHCP setup by looking at your network topology, the devices on the network (for example, routers), and how you want to support your clients in DHCP." />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzakgplanning.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzakgconceptrelayrouter.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzakgexampleparent.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzakgconceptrelayrouter.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzakgconceptsupport.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzakgconceptleases.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzakgconceptbootp.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzakgconceptoptions.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzakgconceptddns.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="../rzakk/rzakkkickoff.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzakgscenario5.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzakgscenario6.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzakgproblemnoip.htm" />
|
||
|
|
<meta name="copyright" content="(C) Copyright IBM Corporation 2004, 2006" />
|
||
|
|
<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 2004, 2006" />
|
||
|
|
<meta name="DC.Format" content="XHTML" />
|
||
|
|
<meta name="DC.Identifier" content="rzakgplanningdemands" />
|
||
|
|
<meta name="DC.Language" content="en-us" />
|
||
|
|
<!-- All rights reserved. Licensed Materials Property of IBM -->
|
||
|
|
<!-- US Government Users Restricted Rights -->
|
||
|
|
<!-- Use, duplication or disclosure restricted by -->
|
||
|
|
<!-- GSA ADP Schedule Contract with IBM Corp. -->
|
||
|
|
<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
|
||
|
|
<link rel="stylesheet" type="text/css" href="./ic.css" />
|
||
|
|
<title>Network topology considerations</title>
|
||
|
|
</head>
|
||
|
|
<body id="rzakgplanningdemands"><a name="rzakgplanningdemands"><!-- --></a>
|
||
|
|
<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
|
||
|
|
<h1 class="topictitle1">Network topology considerations</h1>
|
||
|
|
<div><p>You can plan for most of the DHCP setup by looking at your network
|
||
|
|
topology, the devices on the network (for example, routers), and how you want
|
||
|
|
to support your clients in DHCP.</p>
|
||
|
|
<div class="section"><h4 class="sectiontitle">Understand your network topology</h4><p>One of the most
|
||
|
|
important aspects of planning a DHCP implementation is understanding you network
|
||
|
|
layout or topology. When you understand your network topology, you will be
|
||
|
|
able to quickly identify the IP address ranges for DHCP, the configuration
|
||
|
|
information that each client needs, the devices that need to be configured
|
||
|
|
to forward DHCP messages, and whether DHCP can work with your DNS or PPP servers.
|
||
|
|
Depending on the complexity of your network, you might even want to sketch
|
||
|
|
your network topology on a piece of scrap paper. You should include all of
|
||
|
|
the LANs, the devices that connect the LANs, and the IP addresses for devices
|
||
|
|
and clients (for example, a printer) that need a defined IP address. You might
|
||
|
|
want to look at some of the DHCP examples to help you sketch out your network
|
||
|
|
topology.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"><h4 class="sectiontitle">Determine the number of DHCP servers</h4><p>Even with a
|
||
|
|
complex network, you can still manage all of your network clients using only
|
||
|
|
one DHCP server. Depending on your network topology, you might need to set
|
||
|
|
up a few DHCP/BOOTP relay agents or enable your routers to forward DHCP packets
|
||
|
|
to make it work. </p>
|
||
|
|
<p>Using only one DHCP server for your entire network
|
||
|
|
will centralize host configuration management for all of your clients. However,
|
||
|
|
there are cases where you might want to consider using multiple DHCP servers
|
||
|
|
in your network.</p>
|
||
|
|
<p>To avoid a single point of failure, you can configure
|
||
|
|
two or more DHCP servers to serve the same subnet. If one server fails, the
|
||
|
|
other can continue to serve the subnet. Each of the DHCP servers must be accessible
|
||
|
|
either by direct attachment to the subnet or by using a DHCP/BOOTP relay agent.</p>
|
||
|
|
<p>Because
|
||
|
|
two DHCP servers cannot serve the same addresses, address pools defined for
|
||
|
|
a subnet must be unique across DHCP servers. Therefore, when using two or
|
||
|
|
more DHCP servers to serve a particular subnet, the complete list of addresses
|
||
|
|
for that subnet must be divided among the servers. For example, you can configure
|
||
|
|
one server with an address pool consisting of 70% of the available addresses
|
||
|
|
for the subnet and the other server with an address pool consisting of the
|
||
|
|
remaining 30% of the available addresses.</p>
|
||
|
|
<p>Using multiple DHCP servers
|
||
|
|
decreases the probability of having a DHCP-related network access failure,
|
||
|
|
but it does not guarantee against it. If a DHCP server for a particular subnet
|
||
|
|
fails, the other DHCP server might not be able to service all the requests
|
||
|
|
from new clients, which might, for example, exhaust the server's limited pool
|
||
|
|
of available addresses.</p>
|
||
|
|
<p>If you are considering multiple DHCP servers,
|
||
|
|
remember that multiple DHCP servers cannot share any of the same addresses.
|
||
|
|
If you use more than one DHCP server in your network, each server must be
|
||
|
|
configured with their own unique IP address ranges.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"><h4 class="sectiontitle">Identify the IP addresses that your DHCP server should manage</h4><p>Using
|
||
|
|
your network topology, you should start documenting which network address
|
||
|
|
ranges you want the DHCP server to manage. You should identify which devices
|
||
|
|
have a manually configured IP addresses (for example, the router's IP address)
|
||
|
|
that you want to exclude from the DHCP's address pool.</p>
|
||
|
|
<p>In addition,
|
||
|
|
you will want to consider whether these addresses should be assigned dynamically
|
||
|
|
by the DHCP server or if you want to assign a specific IP address to certain
|
||
|
|
clients. You might want to reserve a specific address and configuration parameters
|
||
|
|
for a specific client on a particular subnet, such as a file server. Or, you
|
||
|
|
might want to map all of your clients to a specific IP address. Refer to DHCP
|
||
|
|
client support for more information about assigning IP addresses dynamically
|
||
|
|
versus statically.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"><h4 class="sectiontitle">Determine the lease time for the IP addresses</h4><p>The
|
||
|
|
default lease time for the DHCP server is 24 hours. The duration for which
|
||
|
|
you set the lease time on your DHCP server depends on several factors. You
|
||
|
|
will need to consider your goals, your site's usage patterns, and service
|
||
|
|
arrangements for your DHCP server. For more information to help you determine
|
||
|
|
the lease time for your DHCP clients, refer to Leases.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"><h4 class="sectiontitle">Support BOOTP clients</h4><p>If you are currently using
|
||
|
|
a BOOTP server, consider that the DHCP server can replace the BOOTP server
|
||
|
|
on your network with little or no impact to your BOOTP clients. There are
|
||
|
|
three options for you if you have BOOTP clients currently on your network.</p>
|
||
|
|
<p>The
|
||
|
|
easiest option is to configure your DHCP server to support BOOTP clients.
|
||
|
|
When you use DHCP to support your BOOTP clients, each BOOTP client is essentially
|
||
|
|
being mapped to a single IP address, and that address is therefore not re-usable
|
||
|
|
by another client. The advantage, however, of using DHCP in this case is that
|
||
|
|
there is no need to configure a one-to-one mapping of BOOTP clients to IP
|
||
|
|
addresses. The DHCP server will still dynamically assign an IP addresses to
|
||
|
|
the BOOTP client from the address pool. After the IP address is assigned to
|
||
|
|
the BOOTP client, it is permanently reserved for use by that client until
|
||
|
|
you explicitly delete the address reservation. This is a good option if you
|
||
|
|
have a large number of BOOTP clients in your network.</p>
|
||
|
|
<p>Another option
|
||
|
|
is to migrate your iSeries™ BOOTP server configuration to the DHCP server.
|
||
|
|
A DHCP client will be created for each BOOTP client listed in the BOOTP server
|
||
|
|
configuration. In this option, it is recommended that you reconfigure your
|
||
|
|
clients to be DHCP clients. However, when you migrate your BOOTP configuration
|
||
|
|
to DHCP, the DHCP address assignments will work for either a BOOTP or DHCP
|
||
|
|
client. This might be a good option to transition your BOOTP clients to DHCP.
|
||
|
|
Your BOOTP clients will still be supported during the process of reconfiguring
|
||
|
|
them to DHCP.</p>
|
||
|
|
<p>Eventually, you might want to do the third option: change
|
||
|
|
each BOOTP client to DHCP and configure DHCP to dynamically assign them addresses.
|
||
|
|
Essentially, this option removes BOOTP entirely from the network.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"><h4 class="sectiontitle">Identify the configuration information for the network clients</h4><p>Using
|
||
|
|
your network topology layout, you can clearly see the devices (for example,
|
||
|
|
routers) that must be identified in the DHCP configuration. In addition, you
|
||
|
|
should identify other servers in your network, such as the Domain Name System
|
||
|
|
(DNS) server, that your clients might need to know about. You can either specify
|
||
|
|
this information for the entire network, a specific subnet, or a specific
|
||
|
|
client regardless of the subnet.</p>
|
||
|
|
<p>If you have devices that apply to many
|
||
|
|
clients, you will want to specify them at the highest level possible (for
|
||
|
|
example, at the Global level for the entire network, or at the subnet level
|
||
|
|
for a specific subnet). This will minimize the changes you will need to make
|
||
|
|
to the DHCP configuration when the device changes. If you have specified the
|
||
|
|
same router, for example, for every client in your network, you need to change
|
||
|
|
the configuration for every client when the router has changed. However, if
|
||
|
|
you have specified the router at the global level (all of the clients will
|
||
|
|
inherit this configuration information), you only need to change the information
|
||
|
|
once and the information is changed for all clients.</p>
|
||
|
|
<p>Some of your clients
|
||
|
|
might have unique TCP/IP configuration requirements that requires information
|
||
|
|
to be configured at the client level. DHCP can recognize those clients and
|
||
|
|
provide the unique configuration data to them. This is not only true for the
|
||
|
|
configuration options, but also for the lease time and IP address. For example,
|
||
|
|
a client might need a longer lease time that all of the other clients. Or,
|
||
|
|
maybe only one client, such as a file server, needs a dedicated IP address.
|
||
|
|
Identifying those clients up front and what unique information they require
|
||
|
|
will help you when you start configuring the DHCP server.</p>
|
||
|
|
<p>For
|
||
|
|
a quick reference to all of the configuration options, refer to <a href="rzakgconceptoptions.htm#rzakgconceptoptions">DHCP options lookup</a>.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"><h4 class="sectiontitle">Use dynamic DNS with your DHCP server</h4><p>If you are
|
||
|
|
currently using a DNS server to manage all of your client's host names and
|
||
|
|
IP addresses, you will definitely want to reconfigure your DNS server to accept
|
||
|
|
dynamic updates from DHCP. If you use Dynamic DNS, the clients will not notice
|
||
|
|
any interruption or changes in the DNS service when you switch over to DHCP.
|
||
|
|
For more information about using DHCP with your DNS server, refer to Dynamic
|
||
|
|
updates.</p>
|
||
|
|
<p>If you are not currently using a DNS server, you might want
|
||
|
|
to consider adding a DNS server when you add the DHCP server. You can read
|
||
|
|
the DNS topic to find out more about DNS benefits and requirements in the
|
||
|
|
information center.</p>
|
||
|
|
</div>
|
||
|
|
<div class="section"><h4 class="sectiontitle">Use DHCP for your remote clients</h4><p>If you have any
|
||
|
|
remote clients that connect to your network using PPP, you can set up DHCP
|
||
|
|
to dynamically assign an IP address to them when they connect to the network.
|
||
|
|
To see some examples of networks where this might be useful, see Example:
|
||
|
|
PPP and DHCP on a single iSeries Server or Example: DHCP and PPP profile on
|
||
|
|
different iSeries servers.
|
||
|
|
These examples also explain how to set up the network to use PPP and DHCP
|
||
|
|
together for your remote clients.</p>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div>
|
||
|
|
<div class="familylinks">
|
||
|
|
<div class="parentlink"><strong>Parent topic:</strong> <a href="rzakgplanning.htm" title="There are several steps you must take to plan how DHCP should be set up for your network.">Plan for DHCP</a></div>
|
||
|
|
</div>
|
||
|
|
<div class="relconcepts"><strong>Related concepts</strong><br />
|
||
|
|
<div><a href="rzakgconceptrelayrouter.htm" title="You might need to use a DHCP relay agent in your network; sometimes a router is sufficient. You can use both a DHCP relay agent and a router to efficiently and securely transfer data throughout the network.">Relay agents and routers</a></div>
|
||
|
|
<div><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>
|
||
|
|
<div><a href="rzakgconceptsupport.htm" title="Using DHCP, you can manage each client in your network individually, rather than managing all of the clients as a large group (subnet).">DHCP client support</a></div>
|
||
|
|
<div><a href="rzakgconceptleases.htm" title="You can find what DHCP leases are and some questions are provided for you to consider when determining the lease time for your DHCP clients.">Leases</a></div>
|
||
|
|
<div><a href="rzakgconceptbootp.htm" title="This topic describes what BOOTP is, and gives some history about BOOTP and DHCP.">BOOTP</a></div>
|
||
|
|
<div><a href="rzakgconceptddns.htm" title="You can use your DHCP server in conjunction with your DNS server to dynamically update the client information in the DNS when DHCP assigns the client an IP address.">Dynamic updates</a></div>
|
||
|
|
<div><a href="../rzakk/rzakkkickoff.htm">DNS</a></div>
|
||
|
|
<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>
|
||
|
|
</div>
|
||
|
|
<div class="relref"><strong>Related reference</strong><br />
|
||
|
|
<div><a href="rzakgconceptoptions.htm" title="DHCP has many configuration options that can be sent to the client when they request information from the DHCP server. You can use a lookup tool that describes all of the DHCP options.">DHCP options lookup</a></div>
|
||
|
|
<div><a href="rzakgscenario5.htm" title="You can learn how to set up the iSeries server as a DHCP server for a LAN and a remote dial-in client.">Example: PPP and DHCP on a single iSeries server</a></div>
|
||
|
|
<div><a href="rzakgscenario6.htm" title="You can learn how to set up two iSeries servers as the network DHCP server and a DHCP/BOOTP relay agent for two LANs and remote dial-in clients.">Example: DHCP and PPP profile on different iSeries servers</a></div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</body>
|
||
|
|
</html>
|