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Guidelines for Configuring Support for DHCP Duplicate Clients
This topic describes the guidelines for configuring 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.
- 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.
For the Layer 3 wholesale model:
- The wholesaler and retailer logical system/routing instances must have the same duplicate-clients-on-interface statement configuration.
- For DHCP relay, the wholesaler and the retailer routing contexts must both be configured with the Agent Circuit ID suboption (suboption 1) in option 82.
