Table Of Contents

Configuring DHCP on the GGSN

Configuring DHCP Server Communication Globally

Configuring DHCP at the GPRS Configuration Level

Specifying a DHCP Server for All Access Points

Specifying a DHCP Server for a Particular Access Point

Configuring DHCP on the GGSN

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This chapter describes how to configure the Dynamic Host Configuration Protocol (DHCP) on the Gateway General Packet Radio Service (GPRS) Support Node (GGSN). The GGSN uses DHCP to assign IP addresses to mobile station users who need to access the PDN.

For a complete description of the GPRS commands in this chapter, refer to the Cisco IOS Mobile Wireless Command Reference. To locate documentation of other commands that appear in this chapter, use the command reference master index or search online.

This chapter includes the following sections:

•Configuring DHCP Server Communication Globally (Required)

•Configuring DHCP at the GPRS Configuration Level (Optional)

Configuring DHCP Server Communication Globally

This section describes how to configure a global DHCP server host that the GGSN can use to assign IP addresses to mobile users. You can configure additional DHCP server communication at the GPRS configuration level.

To globally configure DHCP server communication on the router, use the following commands beginning in global configuration mode:

	Command	Purpose
Step 1	router(config)# ip address-pool {dhcp-proxy-client | local}	Specifies an IP address pool mechanism, where: •dhcp-proxy-client—Specifies the router as the proxy-client between a third-party DHCP server and peers connecting to the router. •local—Specifies the local address pool named "default". Note There is no default option for the ip address-pool command. If you configure a local address pool using the local keyword, you can also configure the optional commands in Step 4 and Step 5.
Step 2	router(config)# ip dhcp-server {ip-address | name}	Specifies the IP address or name of a DHCP server.
Step 3	router(config)# ip dhcp excluded address low-address [high-address]	(Optional) Specifies IP addresses that a DHCP server should not assign to DHCP clients, where: •low-address—Specifies the first IP address in an excluded address range. This address is typically the address of the DHCP server itself. •high-address—(Optional) Specifies the last IP address in the excluded address range.
Step 4	router(config)# ip dhcp pool name	(Optional—Supports ip address-pool local command only.) Configures a DHCP address pool and enters DHCP pool configuration mode, where name can be either a symbolic string (such as "engineering") or an integer (such as 0).
Step 5	router(config-dhcp)# network network-number [mask | /prefix-length]	(Optional—Supports ip address-pool local command only.) Specifies the subnet network number and mask of the DHCP address pool. The prefix length specifies the number of bits that comprise the address prefix. The prefix is an alternative way of specifying the network mask of the client. The prefix length must be preceded by a forward slash (/).

For more information about configuring global DHCP services, refer to the Cisco IOS IP Configuration Guide, Cisco IOS IP Command References, and the Cisco IOS Dial Technologies Command Reference publications.

Configuring DHCP at the GPRS Configuration Level

To complete the DHCP configuration for the GGSN, you can configure DHCP at the GPRS configuration level. When you configure DHCP at the GPRS configuration level, you can configure DHCP server communication for all access points, or for a specific access point.

Configuring DHCP at the GPRS configuration level includes the following tasks:

•Specifying a DHCP Server for All Access Points (Optional)

•Specifying a DHCP Server for a Particular Access Point (Optional)

Specifying a DHCP Server for All Access Points

When processing DHCP address allocation, the GGSN software first checks to see whether a DHCP server has been specified at the access-point configuration level. If so, it uses the DHCP server specified at the access point. If no DHCP server is specified at the access-point configuration level, then the GGSN uses the default GPRS DHCP server.

To specify a DHCP server for all GGSN access points, use the following commands beginning in global configuration mode:

	Command	Purpose
Step 1	router(config)# gprs default ip-address-pool {dhcp-proxy-client | radius-client | disable}	Specifies a dynamic address allocation method using IP address pools for the GGSN, where: •dhcp-proxy-client—Specifies that the GGSN dynamically acquires IP addresses for an MS from a DHCP server. Use this keyword to enable DHCP services. •radius-client—Specifies that the GGSN dynamically acquires IP addresses for an MS from a RADIUS server. •disable—Disables dynamic address allocation by the GGSN. There is no default option for this command.
Step 2	router(config)# gprs default dhcp-server {ip-address | name} [{ip-address | name}]	Specifies a primary (and backup) DHCP server from which the GGSN obtains IP address leases for mobile users, where: •ip-address—Specifies the IP address of a DHCP server. The second (optional) ip-address argument specifies the IP address of a backup DHCP server. •name—Specifies the host name of a DHCP server. The second (optional) name argument specifies the host name of a backup DHCP server.

Specifying a DHCP Server for a Particular Access Point

To override the default DHCP server configured for all access points, you can specify a different DHCP server for a particular access point. Or, if you choose not to configure a default GPRS DHCP server, you can specify a DHCP server at each access point.

To specify a DHCP server for a particular access point, use the following commands beginning in access-point configuration mode:

	Command	Purpose
Step 1	router(config-access-point)# ip-address-pool {dhcp-proxy-client | radius-client | disable}	Specifies a dynamic address allocation method using IP address pools for the current access point, where: •dhcp-proxy-client—Specifies that the access point IP address pool is maintained on a DHCP server. Use this keyword to enable DHCP services. •radius-client—Specifies that the access point IP address pool is allocated through a RADIUS server. •disable—Disables dynamic address allocation for the current access point. There is no default option for this command.
Step 2	router(config-access-point)# dhcp-server {ip-address | name} [{ip-address | name}]	Specifies a primary (and backup) DHCP server that the GGSN uses at a particular access point to obtain IP address leases for mobile users for access to a PDN, where: •ip-address—Specifies the IP address of a DHCP server. The second (optional) ip-address argument specifies the IP address of a backup DHCP server. •name—Specifies the host name of a DHCP server. The second (optional) name argument specifies the host name of a backup DHCP server.