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DHCPv6 Duplicate Client Management

DHCPv6 Duplicate Client DUIDs

The DHCP unique identifier (DUID) is used to identify a client for the proper application of configuration parameters. The DUID is supposed to be unique across all clients. A duplicate DHCPv6 client occurs when a client attempts to obtain a lease, and that client has the same DUID as an existing DHCPv6 client. Because the DUIDs are supposed to be unique, by default the router treats the request from the duplicate client as a renegotiation by the original client, and replaces the existing client entry with a new entry.

However, in some cases the duplicate request is legitimate, because some network equipment vendors do not guarantee the uniqueness of DUIDs. In these circumstances the router can support the duplication of the DUID by accommodating the new client without affecting the existing client.

Starting in Junos OS Release 16.1, you can enable duplicate DHCPv6 client support. When enabled, the router uses the clients’ underlying (incoming) interfaces to differentiate between clients with the same DUID. The router can then create a new client entry for the duplicate client and grant it a lease. The router retains the existing client entry with the original lease.

All underlying interface types are supported. Only 1:1 VLANs are supported, because the client requests are received over different underlying interfaces. N:1 VLANs are not supported, because the client requests can be received over the same underlying interface and therefore cannot be differentiated if the DUIDs are the same.

Configuring the Router to Use Underlying Interfaces to Distinguish Between DHCPv6 Duplicate Client DUIDs

DHCPv6 duplicate clients occur when two clients in a subnet have the same DHCP Unique Identifier (DUID).

The following procedure describes how to configure the router to use the client’s underlying (incoming) interface to differentiate between clients with duplicate DUIDs. The first part of the procedure describes the configuration for DHCPv6 relay agent and the second part configures the DHCPv6 local server.

Note:

Duplicate client DUIDs are supported only when the clients use different underlying interfaces, as in the case of 1:1 VLANs. They are not supported when the clients share an underlying interface, as in the case of N:1 VLANs.

Before configuring duplicate client support, you must ensure the following:

  • DHCPv6 relay agent is configured to insert the DHCPv6 Interface-ID option (option 18) in packets forwarded to the DHCPv6 local server.

  • Option 18 specifies the interface name, not the text description of the interface.

  • DHCPv6 local server must echo option 18 in the RELAY-REPLY messages returned to the DHCPv6 relay agent, as is the case for DHCPv6 local server configured on a Juniper Networks router. The relay agent uses the echoed option 18 information to find the client’s interface and construct the client key.

To configure the DHCPv6 relay agent to support duplicate DUIDs:

  1. Specify that you want to configure DHCPv6 relay agent.
  2. Configure DHCPv6 relay agent to insert DHCPv6 option 18 in the packets forwarded to the DHCPv6 local server.
    Note:

    You must not include the use-interface-description statement because it specifies a text description of the interface.

  3. Specify that the DHCPv6 relay agent uses the clients’ incoming interfaces to differentiate between the duplicate DUIDs.

To configure the DHCPv6 local server to support duplicate DUIDs:

  1. Specify that you want to configure DHCPv6 local server.

  2. Configure the DHCPv6 local server to support duplicate clients based on the clients’ incoming interfaces.

Related Documentation

Release History Table
Release
Description
16.1
Starting in Junos OS Release 16.1, you can enable duplicate DHCPv6 client support.