Configuration Guidelines For Using Duplicate Mac Mode; Restrictions For Using Duplicate Mac Mode To Manage Clients - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - BROADBAND ACCESS CONFIGURATION GUIDE 2010-10-12 Configuration Manual

Configuration Guidelines for Using Duplicate MAC Mode

Restrictions for Using Duplicate MAC Mode to Manage Clients

Copyright © 2010, Juniper Networks, Inc.
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.
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:
Unlike other commands for configuring DHCP external server, the dhcp-external
duplicate-mac-address command applies globally to all instances of the DHCP
external server application on the router, and is not issued on a per-VR basis.
Although the same MAC address can be assigned to more than one DHCP client in the
network, MAC addresses must be unique for each giaddr assigned by a DHCP relay in
the network when duplicate MAC mode is enabled.
As is the case with unique MAC mode, client IP addresses managed by the DHCP
external server application must be unique across all VRs configured on the router.
You can configure DHCP external server to support both duplicate MAC mode (by
issuing the dhcp-external duplicate-mac-address command) and creation of
subscriber state information based on lease renewals (by issuing the ip dhcp-external
server-sync command) simultaneously.
DHCP external server supports the following VR topology changes for DHCP clients
regardless of whether duplicate MAC mode is enabled or disabled:
A client roams across VRs; this might occur, for example, when a laptop computer
moves to a different building in a campus network.
A client is assigned to a different VR; this might occur, for example, when a quality
of service (QoS) policy assigns a client to a different VR during the DHCP binding
process.
When DHCP external server is configured to support unique MAC mode, which is the
default, it uses only the MAC address to uniquely identify DHCP clients. Consequently,
when unique MAC mode is enabled, the MAC addresses for all DHCP clients must be
unique across all VRs configured on the router.
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:
You can issue the dhcp-external duplicate-mac-address command at any time to
enable duplicate MAC mode. However, you cannot issue the no dhcp-external
Chapter 21: Configuring the DHCP External Server Application
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