DHCP External Server Identification of Clients with Duplicate MAC Addresses Overview

You can configure the DHCP external server application to use a combination of the media access control (MAC) address and the gateway IP address (giaddr) to uniquely identify DHCP clients attached to the router. Using this feature enables you to manage DHCP clients in network environments in which MAC addresses are not unique.

In some network environments where the DHCP external server application manages DHCP clients from multiple DHCP relays, the same MAC address might be assigned to more than one DHCP client. This can occur, for example, when network adapters are manufactured with the same hardware address, resulting in duplicate MAC addresses among the DHCP clients attached to the router.

To better manage DHCP clients in network environments with multiple DHCP relays in which MAC addresses are not unique, you can configure the DHCP external server application to use a combination of the MAC address and the giaddr to uniquely identify the clients connected to the router. This setting for DHCP external server is also referred to as duplicate MAC mode.

By default, DHCP external server uses only the MAC address to uniquely identify DHCP clients. The default setting for DHCP external server is also referred to as unique MAC mode.

To enable duplicate MAC mode for the DHCP external server application, you must issue the dhcp-external duplicate-mac-address command from Global Configuration mode. To restore the default behavior and re-enable unique MAC mode, issue the no dhcp-external duplicate-mac-address command.

Configuration Guidelines for Using Duplicate MAC Mode

Observe the following guidelines when you configure the DHCP external server application to use a combination of the MAC address and giaddr to uniquely identify DHCP clients, otherwise known as enabling duplicate MAC mode:

Restrictions for Using Duplicate MAC Mode to Manage Clients

The following restrictions apply when you configure the DHCP external server application to use a combination of the MAC address and giaddr to uniquely identify DHCP clients, otherwise known as duplicate MAC mode:

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