101 lines
7.1 KiB
HTML
101 lines
7.1 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="reference" />
|
||
|
|
<meta name="DC.Title" content="DHCP client-server interaction" />
|
||
|
|
<meta name="abstract" content="A client gets the DHCP information from the server, and specific messages are sent between the client and the server. DHCP obtains and returns leases." />
|
||
|
|
<meta name="description" content="A client gets the DHCP information from the server, and specific messages are sent between the client and the server. DHCP obtains and returns leases." />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzakgconceptparent.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzakgconceptrelayrouter.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzakgconceptleases.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="rzakgconceptinteract" />
|
||
|
|
<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>DHCP client-server interaction</title>
|
||
|
|
</head>
|
||
|
|
<body id="rzakgconceptinteract"><a name="rzakgconceptinteract"><!-- --></a>
|
||
|
|
<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
|
||
|
|
<h1 class="topictitle1">DHCP client-server interaction</h1>
|
||
|
|
<div><p>A client gets the DHCP information from the server, and specific
|
||
|
|
messages are sent between the client and the server. DHCP obtains and returns
|
||
|
|
leases.</p>
|
||
|
|
<div class="section"><p>DHCP provides an automated method for dynamic
|
||
|
|
client configuration. Clients that are DHCP enabled automatically obtain their
|
||
|
|
own IP address and configuration parameters from the server. This process
|
||
|
|
occurs through a series of steps, illustrated in the following figure.</p>
|
||
|
|
<div class="fignone"><span class="figcap">Figure 1. DHCP client-server interaction</span><br /><img src="rzakg508.gif" alt="DHCP client-server interaction." /><br /></div>
|
||
|
|
<dl><dt class="dlterm">Client requests DHCP information: DHCPDISCOVER</dt>
|
||
|
|
<dd>First, the client sends out a DISCOVER message requesting an IP address.
|
||
|
|
The DISCOVER message contains an identifier unique to the client (typically
|
||
|
|
the MAC address). The message might also contain other requests, such as requested
|
||
|
|
options (for example, subnet mask, domain name server, domain name, or static
|
||
|
|
route). The message is sent out as a broadcast. If the network contains routers,
|
||
|
|
those routers can be configured to forward DISCOVER packets to DHCP servers
|
||
|
|
on attached networks.</dd>
|
||
|
|
<dt class="dlterm">DHCP server offers information to client: DHCPOFFER</dt>
|
||
|
|
<dd>Any DHCP server that receives the DISCOVER message might send an OFFER
|
||
|
|
message in response. The DHCP server might not send an OFFER message back
|
||
|
|
to the client for multiple reasons: the most common reasons are
|
||
|
|
that all available addresses are currently leased, the subnet is not configured,
|
||
|
|
or the client is not supported. If the DHCP server sends an OFFER message
|
||
|
|
in response, the DHCPOFFER will contain an available IP address and any other
|
||
|
|
configuration information that is defined in the DHCP setup.</dd>
|
||
|
|
<dt class="dlterm">Client accepts DHCP server offer: DHCPREQUEST</dt>
|
||
|
|
<dd>The client receives OFFER messages from the DHCP servers that responded
|
||
|
|
to the DISCOVER. The client compares the offers with the settings that it
|
||
|
|
requested, and then selects the server that it wants to use. It sends a REQUEST
|
||
|
|
message to accept the offer, indicating which server it selected. This message
|
||
|
|
is broadcast to the entire network to let all DHCP servers know which server
|
||
|
|
was selected.</dd>
|
||
|
|
<dt class="dlterm">DHCP server acknowledges the client and leases the IP address: DHCPACK</dt>
|
||
|
|
<dd>If a server receives a REQUEST message, the server marks the address as
|
||
|
|
leased. Servers that are not selected will return offered addresses to their
|
||
|
|
available pool. The selected server sends the client an acknowledgment (DHCPACK),
|
||
|
|
which contains additional configuration information.<p>The client might now
|
||
|
|
use the IP address and configuration parameters. It will use these settings
|
||
|
|
until its lease expires or until the client sends a DHCPRELEASE message to
|
||
|
|
the server to end the lease.</p>
|
||
|
|
</dd>
|
||
|
|
<dt class="dlterm">Client attempts to renew the lease: DHCPREQUEST, DHCPACK</dt>
|
||
|
|
<dd>The client starts to renew a lease when half of the lease time has passed.
|
||
|
|
The client requests the renewal by sending a REQUEST message to the server.
|
||
|
|
If the server accepts the request, it will send a DHCPACK message back to
|
||
|
|
the client. If the server does not respond to the request, the client might
|
||
|
|
continue to use the IP address and configuration information until the lease
|
||
|
|
expires. As long as the lease is still active, the client and server do not
|
||
|
|
need to go through the DHCPDISCOVER and DHCPREQUEST process. When the lease
|
||
|
|
has expired, the client must start over with the DHCPDISCOVER process.</dd>
|
||
|
|
<dt class="dlterm">Client ends the lease: DHCPRELEASE</dt>
|
||
|
|
<dd>The client ends the lease by sending a RELEASE message to the DHCP server.
|
||
|
|
The server will then return the client's IP address to the available address
|
||
|
|
pool.</dd>
|
||
|
|
</dl>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
<div>
|
||
|
|
<div class="familylinks">
|
||
|
|
<div class="parentlink"><strong>Parent topic:</strong> <a href="rzakgconceptparent.htm" title="DHCP interacts with clients and works in a network.">DHCP concepts</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="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="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>
|
||
|
|
</body>
|
||
|
|
</html>
|