DHCPv6 Option for
IPv4-Embedded Multicast and Unicast IPv6 PrefixesFrance TelecomRennes35000Francemohamed.boucadair@orange.comCiscoChinajacni@jacni.comHuawei Technologies (USA)2330 Central ExpresswaySanta ClaraUSA+1 408 330 4424tina.tsou.zouting@huawei.comThe University of New South WalesNSW 2052SydneyAustraliadxhbupt@gmail.com
Internet
Softwire WGPREFIX64, SSM, ASM, Prefix Discovery, IPv4-Converted IPv6
AddressesThis document defines Dynamic Host Configuration Protocol version 6
(DHCPv6) Option for multicast transition solutions, aiming to convey the
IPv6 prefixes to be used to build unicast and multicast IPv4-embedded
IPv6 addresses.Several solutions (e.g., ) are proposed for
the delivery of multicast services in the context of transition to IPv6.
Even if these solutions may have different applicable use cases, they
all use specific IPv6 addresses to embed IPv4 addresses, for both
multicast group, and multicast source addresses.This document defines a DHCPv6 option
to convey the IPv6 prefixes to be used for constructing these
IPv4-embedded IPv6 addresses.This option can be in particular used in the context of DS-Lite , Stateless A+P
and other IPv4-IPv6 transition techniques.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.This document makes use of the following terms:IPv4-embedded IPv6 address: is an IPv6 address which embeds a 32
bit-encoded IPv4 address . An
IPv4-embedded IPv6 address can be a unicast or a multicast
address.PREFIX64: is an IPv6 prefix used for synthesizing IPv4-embedded
IPv6 addresses. A PREFIX64 can be of unicast or multicast.Note: "64" is used as an abbreviation for IPv6-IPv4
interconnection.ASM_PREFIX64: is a multicast PREFIX64 which belongs to the
Any-Source Multicast (ASM) range.SSM_PREFIX64: is a multicast PREFIX64 which belongs to the
Source-Specific Multicast (SSM, )
range.U_PREFIX64: is a unicast PREFIX64 for building the IPv4-embedded
IPv6 addresses of multicast sources in SSM mode.OPTION_V6_PREFIX64 () conveys the IPv6
prefix(es) to be used (e.g., by a mB4 ) to synthesize
IPv4-embbedded IPv6 addresses.The fields of the option shown in are
as follows:OPTION_V6_PREFIX64 (see ).length of the PREFIX64 option.the prefix-length for the ASM
IPv4-embedded prefix, as an 8-bit unsigned integer (0 to 128). This
field represents the number of valid leading bits in the prefix.this field identifies the IPv6 multicast
prefix to be used to synthesize the IPv4-embedded IPv6 addresses of
the multicast groups in the ASM mode. It is a variable size field
with the length of the field defined by the asm-length field and is
rounded up to the nearest octet boundary. In such case any
additional padding bits must be zeroed. The conveyed multicast IPv6
prefix MUST belong to the ASM range. This prefix is likely to be a
/96.the prefix-length for the SSM
IPv4-embedded prefix, as an 8-bit unsigned integer (0 to 128). This
field represents the number of valid leading bits in the prefix.this field identifies the IPv6 multicast
prefix to be used to synthesize the IPv4-embedded IPv6 addresses of
the multicast groups in the SSM mode. It is a variable size field
with the length of the field defined by the ssm-length field and is
rounded up to the nearest octet boundary. In such case any
additional padding bits must be zeroed. The conveyed multicast IPv6
prefix MUST belong to the SSM range. This prefix is likely to be a
/96.the prefix-length for the IPv6 unicast
prefix to be used to synthesize the IPv4-embedded IPv6 addresses of
the multicast sources, as an 8-bit unsigned integer (0 to 128). This
field represents the number of valid leading bits in the prefix.this field identifies the IPv6 unicast
prefix to be used in SSM mode for constructing the IPv4-embedded
IPv6 addresses representing the IPv4 multicast sources in the IPv6
domain. U_PREFIX64 may also be used to extract the IPv4 address from
the received multicast data flows. It is a variable size field with
the length of the field defined by the unicast-length field and is
rounded up to the nearest octet boundary. In such case any
additional padding bits must be zeroed. The address mapping MUST
follow the guidelines documented in .DHCP servers supporting OPTION_V6_PREFIX64 should be configured with
U_PREFIX64 and at least one ASM_PREFIX64 or one SSM_PREFIX64.When ASM_PREFIX64 and SSM_PREFIX64 are configured, the length of
these prefixes must be /96.Both ASM_PREFIX64 and SSM_PREFIX64 may be configured and therefore be
returned to a requesting DHCP client; it is deployment-specific. In
particular, if both SSM and ASM modes are supported, ASM_PREFIX64 and
SSM_PREFIX64 prefixes must be configured. For SSM deployments, both
SSM_PREFIX64 and U_PREFIX64 should be configured.To retrieve the IPv6 prefixes that will be used to synthesize unicast
and multicast IPv4-embedded IPv6 addresses, the DHCPv6 client MUST
include OPTION_V6_PREFIX64 in its OPTION_ORO. If the DHCPv6 client
receives more than one OPTION_V6_PREFIX64 option from the DHCPv6
server:If all the enclosed IPv4-embedded IPv6 multicast prefixes have
the same scope, the first instance of the option MUST be used.If each enclosed IPv4-embedded IPv6 multicast prefix has a
distinct scope, the client MUST select the appropriate IPv4-embedded
IPv6 multicast prefix having a scope matching the IPv4 multicast
address used to synthesize an IPv4-embedded IPv6 multicast
address.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 in the response received from the DHCPv6 server.If the asm-length field is non-null, the IPv6 prefix identified by
ASM_PREFIX64 is used to synthesize IPv4-embedded IPv6 multicast
addresses in the ASM range. This is achieved by concatenating the
ASM_PREFIX64 and the IPv4 multicast address; the Pv4 multicast address
is inserted in the last 32 bits of the IPv4-embedded IPv6 multicast
address.If the ssm-length field is non-null, the IPv6 prefix identified by
SSM_PREFIX64 is used to synthesize IPv4-embedded IPv6 multicast
addresses in the SSM range. This is achieved by concatenating the
SSM_PREFIX64 and the IPv4 multicast address; the Pv4 multicast address
is inserted in the last 32 bits of the IPv4-embedded IPv6 multicast
address.If the unicast-length field is non-null, the IPv6 prefix identified
by U_PREFIX64 field is used to synthesize IPv4-embedded IPv6 unicast
addresses as specified in .The security considerations documented in and are to be
considered.Particular thanks to C. Jacquenet, S. Venaas, B. Volz and T. Taylor
for their review.Authors of this document request IANA to assign a new DHCPv6 option
in the registry maintained in
http://www.iana.org/assignments/dhcpv6-parameters: