When the DHCPv6 Relay Agent is relaying to a third party DHCPv6 external server, following conditions should be met:
The third party DHCPv6 server must return a unique IA_PD IPv6 delegated prefix (/64 or lower) for each allocation. The length of the IA_PD IPv6 delegated prefix must match the delegated-prefix-len configured on the subscriber interface on the 7750 DHCP L3 relay. This length is also included in the Relay-Forward message as PFX_LEN option (3) in a Vendor-Specific-Information-Option (17).
For IPv6oE routed CPEs, the 3rd party DHCPv6 server must return a unique IA_NA IPv6 address (/128) from a different /64 subnet for each allocation.
For IPv6oE hosts behind bridged CPE's
the third party DHCPv6 server must return a unique IA_NA IPv6 address (/128) from a different /64 subnet for each allocation (host) that belongs to a different CPE.
the third party DHCPv6 server may return a unique IA_NA IPv6 address (/128) from the same /64 subnet for allocations (hosts) that belong to the same CPE and that are attached to the same VLAN (SAP) on the BNG.
Following information is available to the third party DHCPv6 server in a Vendor-Specific-Information-Option (17) included in the Relay-Forward message:
WAN_POOL option (1) contains the pool name from which the IA_NA IPv6 address should be allocated.
PFX_POOL option (2) contains the pool name from which the IA_PD IPv6 delegated prefix should be allocated.
PFX_LEN option (3): contains the IA_PD IPv6 delegated prefix length that should be allocated.