DHCPv6 Option for IPv4-Embedded Multicast and Unicast IPv6 Prefixes
Extracted elements (18)
The option was designed as a single combined structure rather than three distinct DHCPv6 options to avoid the unintended side effect of enabling unicast Prefix64 discovery in multicast-disabled environments, which would conflict with the recommended Well-Known DNS Name heuristic discovery method for unicast-only environments (RFC 7051 Section 6).
OPTION_V6_PREFIX64 is applicable in the context of Dual-Stack Lite (DS-Lite, RFC 6333), Stateless Address plus Port (A+P, RFC 6346), and other IPv4-IPv6 transition techniques that use IPv4-embedded IPv6 addresses.
If asm-length, ssm-length, and unicast-length fields are all set to 0, the DHCPv6 client MUST behave as if OPTION_V6_PREFIX64 had not been received.
If at least two received OPTION_V6_PREFIX64 options convey IPv6 multicast prefixes with the same scope, those options MUST be discarded.
If the client receives multiple OPTION_V6_PREFIX64 options where each enclosed IPv6 multicast prefix has a distinct scope, the client MUST select the appropriate prefix whose scope matches the IPv4 multicast address being synthesized.
The address mapping for uPrefix64 MUST follow the guidelines documented in RFC 6052.
The asm-length field MUST be set to 96, representing the prefix length for the ASM IPv4-embedded prefix.
The conveyed ASM multicast IPv6 prefix MUST belong to the ASM range.
The conveyed SSM multicast IPv6 prefix MUST belong to the SSM range.
The DHCPv6 client MUST include the OPTION_V6_PREFIX64 code in its OPTION_ORO to retrieve the IPv6 prefixes for synthesizing unicast and multicast IPv4-embedded IPv6 addresses.
The ssm-length field MUST be set to 96, representing the prefix length for the SSM IPv4-embedded prefix.
The unicast-length field MUST be one of 32, 40, 48, 56, 64, or 96, as specified in RFC 6052.
Multiple instances of OPTION_V6_PREFIX64 may be returned to a DHCPv6 client to support distinct IPv6 multicast address scopes (per RFC 7346) when translating IPv4 multicast addresses with scope preservation.
OPTION_V6_PREFIX64 is a DHCPv6 option (code 113) that conveys IPv6 prefixes used to synthesize IPv4-embedded IPv6 addresses for multicast and unicast in IPv4-IPv6 transition scenarios. It carries ASM_mPrefix64, SSM_mPrefix64, and uPrefix64 fields.
uPrefix64 is the IPv6 unicast prefix used in SSM mode to construct IPv4-embedded IPv6 addresses representing IPv4 multicast sources in the IPv6 domain; it may also be used to extract the IPv4 address from received multicast data flows.
IANA assigned option code 113 to OPTION_V6_PREFIX64 in the 'Dynamic Host Configuration Protocol for IPv6 (DHCPv6)' registry.
The security considerations documented in RFC 3315 (DHCPv6) and RFC 6052 (IPv6 Addressing of IPv4/IPv6 Translators) apply to this option.
The OPTION_V6_PREFIX64 option contains: option-code (16-bit), option-length (16-bit), asm-length (8-bit unsigned), ASM_mPrefix64 (variable), ssm-length (8-bit unsigned), SSM_mPrefix64 (variable), unicast-length (8-bit unsigned), and uPrefix64 (variable, rounded up to nearest octet boundary with zero padding).