Cisco IOS Dynamic Host Configuration Protocol Client

Feature Overview

Benefits

Cisco IOS Dynamic Host Configuration Protocol Client

This feature module describes the Cisco IOS Dynamic Host Configuration Protocol (DHCP) Client feature and includes the following sections:

Feature Overview

The Cisco DHCP Client is a host requesting configuration parameters, such as an IP address, from a DHCP server.

Figure 1 shows the basic steps that occur when a DHCP client requests an IP address from a DHCP server. The client, Host A, sends a DHCPDISCOVER broadcast message to locate a Cisco IOS DHCP server. A DHCP server offers configuration parameters (such as an IP address, a MAC address, a domain name, and a lease for the IP address) to the client in a DHCPOFFER unicast message.

Figure 1: DHCP Request for an IP Address from a DHCP Server

The client returns a formal request for the offered IP address to the DHCP server in a DH CPREQUEST broadcast message. The DHCP server confirms that the IP address has been allocated to the client by returning a DH CPACK unicast message to the client.

The Cisco IOS DHCP client now enables you to obtain an IP address from a DHCP server dynamically using the DHCP protocol as specified in RFC 2131. Initially, only Ethernet interfaces are supported; work is in progress to support all interface types.

Benefits

Reduces time to configure and deploy
Reduces configuration errors
Enables customers to centrally control the IP address assigned to a Cisco IOS router

Supported Platforms

Catalyst 5000 family switches with an installed Route Switch Module
Catalyst 6000 family switches with an installed MultiLayer Switch Feature Card
Catalyst 8500 series
Cisco 800 series
Cisco 1000 series
Cisco 1400 series
Cisco 1600 series
Cisco 1700 series (support for the Cisco 1700 series was added in Cisco IOS Release 12.0(2)T)
Cisco 2500 series
Cisco 2600 series
Cisco 3600 series
Cisco 3800 series
Cisco MC3810 series
Cisco 4000 series
Cisco AS5100 access server
Cisco AS5200 universal access server
Cisco AS5300 universal access server
Cisco 7000 series
Cisco 7100 series
Cisco 7200 series
Cisco MGX 8800 with an installed Route Processor Module
Cisco 12000 series
Cisco uBR900 series
Cisco uBR7200 series

Supported Standards, MIBs, and RFCs

Standards

No new or modified standards are supported by this feature.

MIBs

No new or modified MIBs are supported by this feature.

For descriptions of supported MIBs, see the Cisco MIB web site on CCO at http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml.

RFCs

RFC 951, Bootstrap Protocol (BOOTP)
RFC 1542, Clarifications and Extensions for the Bootstrap Protocol
RFC 2131, Dynamic Host Configuration Protocol
RFC 2132, DHCP Options and BOOTP Vendor Extensions

Configuration Tasks

See the following section for configuration tasks for the Cisco IOS Dynamic Host Control Protocol Client feature:

Configuring the DHCP Client on Ethernet Interfaces

Configuring the DHCP Client on Ethernet Interfaces

Command Purpose

Router(config-if)# ip address dhcp
Specifies that the Ethernet interface acquires an IP address through DHCP.

Command	Purpose
Router(config-if)# ip address dhcp	Specifies that the Ethernet interface acquires an IP address through DHCP.

Configuration Examples

Figure 2 shows a simple network diagram of a DHCP client on an Ethernet LAN.

Figure 2: Topology Showing DHCP Client with
Ethernet Interface

On the DHCP server, configure:

ip dhcp pool 1
 network 10.1.1.0 255.255.255.0
 lease 0 0 5

On the DHCP client, configure on interface E2:

interface Ethernet2
 ip address dhcp

This configuration allows the DHCP client to aquire an IP address from the DHCP server through an Ethernet interface.

Command Reference

This section documents the new ip address dhcp command. All other commands used with this feature are documented in the Cisco IOS Release 12.1 Cisco IOS IP and IP Routing Command Reference.

ip address dhcp

To acquire an IP address on an Ethernet interface from the Dynamic Host Configuration Protocol (DHCP), use the ip address dhcp interface configuration command. To deconfigure any address that was acquired, use the no form of this command.

ip address dhcp

no ip address dhcp

Syntax Description

This command has no arguments or keywords.

Defaults

No default behavior or values.

Command Modes

Interface configuration

Command History

Release Modification

12.1(2)T

This command was introduced.

Release	Modification
12.1(2)T	This command was introduced.

Usage Guidelines

The address assigned to the Ethernet interface can be used with the overload Port Address Translation (PAT) of Cisco IOS Network Address Translation (NAT).

Examples

The following example shows an IP address being acquired via DHCP on interface Ethernet2:

interface Ethernet2
 ip address dhcp

Related Commands

Command Description

ip dhcp pool

Configures a DHCP address pool on a Cisco IOS DHCP server and places you in DHCP pool configuration mode.

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