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12.1. Requesting Router Behavior

12.1. Requesting Router Behavior​

The requesting router uses a Request message to populate IA_PDs with prefixes. The requesting router includes one or more IA_PD options in the Request message. The delegating router then returns the prefixes for the IA_PDs to the requesting router in IA_PD options in a Reply message.

The requesting router includes IA_PD options in any Renew, or Rebind messages sent by the requesting router. The IA_PD option includes all of the prefixes the requesting router currently has associated with that IA_PD.

In some circumstances the requesting router may need verification that the delegating router still has a valid binding for the requesting router. Examples of times when a requesting router may ask for such verification include:

  • The requesting router reboots.
  • The requesting router's upstream link flaps.
  • The requesting router is physically disconnected from a wired connection.

If such verification is needed the requesting router MUST initiate a Rebind/Reply message exchange as described in section 18.1.4, "Creation and Transmission of Rebind Messages" of RFC 3315, with the exception that the retransmission parameters should be set as for the Confirm message, described in section 18.1.2, "Creation and Transmission of Confirm Messages" of RFC 3315. The requesting router includes any IA_PDs, along with prefixes associated with those IA_PDs in its Rebind message.

Each prefix has valid and preferred lifetimes whose durations are specified in the IA_PD Prefix option for that prefix. The requesting router uses Renew and Rebind messages to request the extension of the lifetimes of a delegated prefix.

The requesting router uses a Release message to return a delegated prefix to a delegating router. The prefixes to be released MUST be included in the IA_PDs.

The Confirm and Decline message types are not used with Prefix Delegation.

Upon the receipt of a valid Reply message, for each IA_PD the requesting router assigns a subnet from each of the delegated prefixes to each of the links to which the associated interfaces are attached, with the following exception: the requesting router MUST NOT assign any delegated prefixes or subnets from the delegated prefix(es) to the link through which it received the DHCP message from the delegating router.

When a requesting router subnets a delegated prefix, it must assign additional bits to the prefix to generate unique, longer prefixes. For example, if the requesting router in Figure 1 were delegated 3FFE:FFFF:0::/48, it might generate 3FFE:FFFF:0:1::/64 and 3FFE:FFFF:0:2::/64 for assignment to the two links in the subscriber network. If the requesting router were delegated 3FFE:FFFF:0::/48 and 3FFE:FFFF:5::/48, it might assign 3FFE:FFFF:0:1::/64 and 3FFE:FFFF:5:1::/64 to one of the links, and 3FFE:FFFF:0:2::/64 and 3FFE:FFFF:5:2::/64 for assignment to the other link.

If the requesting router assigns a delegated prefix to a link to which the router is attached, and begins to send router advertisements for the prefix on the link, the requesting router MUST set the valid lifetime in those advertisements to be no later than the valid lifetime specified in the IA_PD Prefix option. A requesting router MAY use the preferred lifetime specified in the IA_PD Prefix option.

Handling of Status Codes options in received Reply messages is described in section 18.1.8, "Receipt of Reply Messages" of RFC 3315. The NoPrefixAvail Status Code is handled in the same manner as the NoAddrsAvail Status Code.

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