A local DHCPv6 pool server for both addresses (IA_NA) and prefixed (IA_PD) manages the address and prefixes sent to either routing gateways or hosts.
Because IPv6 home networks lack NAT, the IPv6 addresses delegated to a routing gateway are in turn assigned to hosts in the home. These addresses are assigned with reasonably long (but configurable) lifetimes so the loss of the WAN connection does not result in the IPv6 hosts in the LAN losing their IPv6 addresses. One consequence of these long lifetimes is that the IPv6 hosts retains any IPv6 address provided the valid-lifetime is greater than zero. If an operator delegates a prefix and then at a later time delegate a second IPv6 prefix, a host may end up with two or more valid prefixes. This situation affects IPv6 source address selection and may result in impaired service.
To overcome the problems of multiple IPv6 prefixes in the home, the operator must ensure that the individual subscriber has the same IPv6 prefix even across modem reboots (that is, if a subscriber session is destroyed and later re-created, an attempt should be made to use the previously delegated prefix). In Release 8.0, the operator used RADIUS for all address and prefix assignment, but in Release 9.0, with the introduction of the local DHCPv6 server, it requires the 7750 to process and maintain some state even after a session disconnects.
For the DHCPv6 local server to function, a DHCPv6 relay or proxy function must also operate alongside ESM. For the purposes of this document, to relay means to implement a DHCPv6 Relay as indicated in RFC 3315: a relay encapsulates the client DHCP message within a DHCP Relay-Forward message and unicasts it to a specified destination.
A proxy is an internal concept. Unlike a DHCPv6 relay, the DHCPv6 proxy does not encapsulate the client message in a Relay-Forward, nor does it send packets toward the Local DHCPv6 Server. The DHCPv6 proxy is exclusively used as an interface between the RADIUS Access-Accept or local user database lookup and the DHCPv6 client in the consumer device.
The use of the DHCPv6 relay or proxy function depends on the attributes returned from authentication phase (RADIUS or LUDB).
DHCPv6 proxy:
If only the IPv6 address/prefix information is provided (Framed-IPv6-Prefix, Alc-IPv6-Address or Delegated-IPv6-Prefix).
DHCPv6 relay:
If no IPv6 address/prefix (Framed-IPv6-Prefix, Alc-IPv6-Address or Delegated-IPv6-Prefix) and no IPv6 pool (Framed-Pool, Delegated-Pool) information provided.
If no IPv6 address/prefix (Framed-IPv6-Prefix, Alc-IPv6-Address or Delegated-IPv6-Prefix) and IPv6 pool (Framed-Pool, Delegated-Pool) information provided.
If both IPv6 address/prefix (Framed-IPv6-Prefix, Alc-IPv6-Address or Delegated-IPv6-Prefix) and IPv6 pool (Framed-Pool, Delegated-Pool) information are present, the DHCP packet is DROPPED.