Configuring the Cisco IOS XE DHCP Client
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Configuring the Cisco IOS XE DHCP Client

Table Of Contents

Configuring the Cisco IOS XE DHCP Client

Finding Feature Information

Contents

Information About the DHCP Client

DHCP Client Operation

DHCP Client Overview

How to Configure the DHCP Client

Configuring the DHCP Client

DHCP Client Default Behavior

Prerequisites

Troubleshooting Tips

Configuration Examples for the DHCP Client

Configuring the DHCP Client: Example

Customizing the DHCP Client Configuration: Example

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Feature Information for the Cisco IOS XE DHCP Client


Configuring the Cisco IOS XE DHCP Client


First Published: May 2, 2005
Last Updated: May 4, 2009

Cisco IOS XE Dynamic Host Configuration Protocol (DHCP) client software provides the flexibility to include various configuration options for the DHCP client. A DHCP client is defined as an Internet host using DHCP to obtain configuration parameters such as an IP address. This module describes the concepts and tasks needed to configure the Cisco IOS XE DHCP client.

Finding Feature Information

For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for the Cisco IOS XE DHCP Client" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS XE software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

Information About the DHCP Client

Information About the DHCP Client

How to Configure the DHCP Client

Configuration Examples for the DHCP Client

Additional References

Feature Information for the Cisco IOS XE DHCP Client

Information About the DHCP Client

To configure the DHCP client, you must understand the following concepts:

DHCP Client Operation

DHCP Client Overview

DHCP Client Operation

DHCP provides a framework for passing configuration information to hosts on a TCP/IP network. A DHCP client is an Internet host using DHCP to obtain configuration parameters such as an IP address. 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 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

A DHCP client may receive offers from multiple DHCP servers and can accept any one of the offers; however, the client usually accepts the first offer it receives. Additionally, the offer from the DHCP server is not a guarantee that the IP address will be allocated to the client; however, the server usually reserves the address until the client has had a chance to formally request the address.

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

DHCP Client Overview

The configurable DHCP client functionality allows a DHCP client to use a user-specified client identifier, class identifier, or suggested lease time when requesting an address from a DHCP server.

Configuration parameters and other control information are carried in tagged data items that are stored in the options field of the DHCP message. The DHCP client provides flexibility by allowing the following options to be configured for a DHCP client:

Option 12This option specifies the name of the client. The name may or may not be qualified with the local domain.

Option 51This option is used in a client request (DHCPDISCOVER or DHCPREQUEST) to allow the client to request a lease time for the IP address.

Option 55This option allows the DHCP client to request certain options from the DHCP server. The ip dhcp client request command allows the system administrator to turn off some of the requested options, thus removing them from the request list.

Option 60This option allows the user to configure the vendor class identifier string to use in the DHCP interaction.

Option 61This option is used by DHCP clients to specify their unique identifier. DHCP servers use this value to index their database of address bindings. This value is expected to be unique for all clients in an administrative domain.

How to Configure the DHCP Client

This section contains the following tasks:

Configuring the DHCP Client

Configuration Examples for the DHCP Client

Configuring the DHCP Client

Perform this task to configure the DHCP client.

DHCP Client Default Behavior

Cisco routers running Cisco IOS XE software include DHCP server and relay agent software, which are enabled by default. Your router can act as both the DHCP client and DHCP server. Use the ip address dhcp interface command to obtain IP address information for the configured interface.

Prerequisites

You must configure the ip dhcp client commands before entering the ip address dhcp command on an interface to ensure that the DHCPDISCOVER messages that are generated contain the correct option values. The ip dhcp client commands are checked only when an IP address is acquired from DHCP. If any of the ip dhcp client commands are entered after an IP address has been acquired from DHCP, it will not take effect until the next time the router acquires an IP address from DHCP. This means that the new configuration will only take effect after the ip address dhcp command command has been configured.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface type number

4. ip dhcp client client-id {interface-name | ascii string | hex string}

5. ip dhcp client class-id {string | hex string}

6. ip dhcp client lease days [hours] [minutes]

7. ip dhcp client hostname host-name

8. [no] ip dhcp client request option-name

9. ip address dhcp

10. exit

11. ip dhcp compatibility lease-query client {cisco | standard}

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

interface type number

Example:

Router(config)# interface GigabitEthernet 0/0/1

Configures an interface type and enters interface configuration mode.

Step 4 

ip dhcp client client-id {interface-name | ascii string | hex string}

Example:

Router(config-if)# ip dhcp client client-id ascii mytest1

(Optional) Specifies the client identifier.

When you specify the no form of this command, the configuration is removed and the system returns to using the default form. It is not possible to configure the system to not include a client identifier.

Step 5 

ip dhcp client class-id {string | hex string}

Example:

Router(config-if)# ip dhcp client class-id my-class-id

(Optional) Specifies the class identifier.

Step 6 

ip dhcp client lease days [hours] [minutes]

Example:

Router(config-if)# ip dhcp client lease 2

(Optional) Configures the duration of the lease for an IP address that is requested from a DHCP client to a DHCP server.

Step 7 

ip dhcp client hostname host-name

Example:

Router(config-if)# ip dhcp client hostname router1

(Optional) Specifies or modifies the host name sent in the DHCP message.

Step 8 

[no] ip dhcp client request option-name

Example:

Router(config-if)# no ip dhcp client request tftp-server-address

(Optional) Configures a DHCP client to request an option from a DHCP server.

The option name can be tftp-server-address, netbios-nameserver, vendor-specific, static-route, domain-name, dns-nameserver, or router. By default, all these options are requested. The no form of the command instructs the system to not request certain options.

Step 9 

ip address dhcp

Example:

Router(config-if)# ip address dhcp

Acquires an IP address on an interface from DHCP.

Step 10 

exit

Example:

Router(config-if)# exit

(Optional) Exits interface configuration mode.

Step 11 

ip dhcp compatibility lease-query client {cisco | standard}

Example:

Router(config)# ip dhcp compatibility lease-query client standard

(Optional) Configures a DHCP client to send a lease query according to RFC 4388 standard.

Troubleshooting Tips

To verify the configuration, you can use the debug dhcp detail EXEC command to display the DHCP packets that were sent and received. To display the server side of the DHCP interaction, use the debug ip dhcp server packets command.

Configuration Examples for the DHCP Client

This section provides the following configuration examples:

Configuring the DHCP Client: Example

Customizing the DHCP Client Configuration: Example

Configuring the DHCP Client: Example

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

Figure 2 Topology Showing DHCP Client with GigabitEthernet Interface

On the DHCP server, the configuration is as follows:

ip dhcp pool 1
 network 10.1.1.0 255.255.255.0
 lease 1 6 

On the DHCP client, the configuration is as follows on interface GigabitEthernet 0/0/0:

interface GigabitEthernet 0/0/0
 ip address dhcp

This configuration allows the DHCP client to acquire an IP address from the DHCP server through GigabitEthernet interface 0/0/0.

Customizing the DHCP Client Configuration: Example

The following example shows how to customize the DHCP client configuration with various options on GigabitEthernet interface 0/0/1:

interface GigabitEthernet 0/0/1
 ip dhcp client client-id ascii my-test1
 ip dhcp client class-id my-class-id
 ip dhcp client lease 0 1 0
 ip dhcp client hostname sanfran
 no ip dhcp client request tftp-server-address
 ip address dhcp

Additional References

The following sections provide references related to the DHCP client.

Related Documents

Related Topic
Document Title

DHCP commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples.

Cisco IOS IP Addressing Services Command Reference

DHCP conceptual information

"DHCP Overview" module

DHCP server configuration

"Configuring the Cisco IOS XE DHCP Server" module

DHCP server on-demand address pools

"Configuring the DHCP Server On-Demand Address Pool Manager" module

DHCP relay agent configuration

"Configuring the Cisco IOS XE DHCP Relay Agent" module

DHCP advanced features

"Configuring DHCP Services for Accounting and Security"module


Standards

Standards
Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.


MIBs

MIBs
MIBs Link

No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

To locate and download MIBs for selected platforms, Cisco IOS XE software releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs


RFCs

RFCs
Title

RFC 2131

Dynamic Host Configuration Protocol

RFC 2132

DHCP Options and BOOTP Vendor Extensions


Technical Assistance

Description
Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies.

To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds.

Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/techsupport


Feature Information for the Cisco IOS XE DHCP Client

Table 1 lists the features in this module and provides links to specific configuration information.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.


Note Table 1 lists only the Cisco IOS XE software release that introduced support for a given feature in a given Cisco IOS XE software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE software release train also support that feature.


Table 1 Feature Information for the Cisco IOS XE DHCP Client 

Feature Name
Releases
Feature Configuration Information

DHCP Client

Cisco IOS XE Release 2.3

A DHCP client is defined as an Internet host using DHCP to obtain configuration parameters such as an IP address.

The following command was introduced by this feature:
ip address dhcp

Configurable DHCP Client

Cisco IOS XE Release 2.3

The configurable DHCP client functionality allows a DHCP client to use a user-specified client identifier, class identifier, or suggested lease time when requesting an address from a DHCP server.

The following sections provide information about this feature:

Configuring the DHCP Client

The following commands were introduced by this feature: ip dhcp client class-id, ip dhcp client client-id, ip dhcp client hostname, ip dhcp client lease, ip dhcp client request