Guidelines For Configuring Support For Dhcp Duplicate Clients - Juniper ACX1000 Configuration Manual

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Guidelines for Configuring Support for DHCP Duplicate Clients

Copyright © 2017, Juniper Networks, Inc.
By default, a DHCP local server uses the subnet information to differentiate between
duplicate clients. However, in some cases, this level of differentiation is not adequate.
For example, when multiple subinterfaces share the same underlying loopback interface
with the same preferred source address, the interfaces appear to be on the same subnet.
In this situation, the default configuration prevents duplicate clients.
You can provide greater differentiation between duplicate clients by configuring DHCP
to consider the client subinterface when duplicate clients occur. In this optional
configuration, DHCP uniquely identifies:
The subnet on which the client resides
The subinterface on which the client resides
The client within the subnet
Extended DHCP Local Server Overview on page 315
DHCP Local Server Handling of Client Information Request Messages on page 335
Address-Assignment Pools Overview on page 317
Guidelines for Configuring Support for DHCP Duplicate Clients on page 363
Understanding DHCP Client Operation on page 359
This topic describes the guidelines for configuring Dynamic Host Configuration Protocol
(DHCP) to include the client subinterface in order to distinguish between duplicate clients
(clients with the same MAC address or client ID) in a subscriber access environment.
When configuring DHCP duplicate client support, consider the following guidelines:
The optional DHCP duplicate client support feature is used for DHCPv4 clients. For
DHCPv6, client identification is independent of MAC address.
For DHCP relay agent configuration:
DHCP relay must be configured to insert option 82, regardless of whether or not the
incoming packet has option 82.
Option 82 must include the Agent Circuit ID suboption (suboption 1).
Option 82 must be the interface name, not the interface description.
The DHCP server must echo option 82 in the server's reply. This is required because
of the following:
The giaddr inserted by DHCP relay is the same for duplicate clients on different
subinterfaces. The DHCP local server uses option 82 when allocating the IP address.
DHCP relay uses the echoed option 82 to learn the client subinterface and to
construct the client key.
Chapter 10: Configuring DHCP Client and DHCP Server
363