| 6man Working Group | M. Boucadair |
| Internet-Draft | France Telecom |
| Updates: 3306,3956,4291 (if approved) | S. Venaas |
| Intended status: Standards Track | Cisco |
| Expires: February 12, 2015 | August 11, 2014 |
Updates to the IPv6 Multicast Addressing Architecture
draft-ietf-6man-multicast-addr-arch-update-08
This document updates the IPv6 multicast addressing architecture by re-defining the reserved bits as generic flag bits. The document provides also some clarifications related to the use of these flag bits.
This document updates RFC 3956, RFC 3306 and RFC 4291.
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 [RFC2119].
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This document updates the IPv6 addressing architecture [RFC4291] by re-defining reserved bits as generic flag bits (Section 2). The document provides also some clarifications related to the use of these flag bits (Section 3).
This document updates [RFC3956], [RFC3306], and [RFC4291]. These updates are logical consequences of the new processing rules in Section 3.
Textual representation of IPv6 addresses included in the RFC updates follows the recommendation in [RFC5952].
Bits 17-20 of a multicast address, where bit 1 is the most significant bit, are defined in [RFC3956] and [RFC3306] as reserved bits. This document defines these bits as generic flag bits so that they apply to any multicast address. These bits are referred to as ff2 (flag field 2) while the flgs bits in [RFC4291][RFC3956] are renamed to ff1 (flag field 1).
Within this document, flag bits denote both ff1 and ff2.
Defining the bits 17-20 as flags for all IPv6 multicast addresses allows addresses to be treated in a more uniform and generic way, and allows for these bits to be defined in the future for different purposes, irrespective of the specific type of multicast address. For the record, this design choice was initially triggered by the specification in [I-D.ietf-mboned-64-multicast-address-format] which proposed for associating a meaning with one of the reserved bits. Moreover, [I-D.ietf-mboned-64-multicast-address-format] considered also the use of the last remaining flag in ff1 but that approach was abandoned because it is not clear at this stage whether there is other usage scenarios of the flag.
Section 4 specifies the updated structure of the addressing architecture.
Further specification documents may define a meaning for these flag bits.
Some implementations and specification documents do not treat the flag bits as separate bits but tend to use their combined value as a 4-bit integer. This practice is a hurdle for assigning a meaning to the remaining flag bits. Below are listed some examples for illustration purposes:
To avoid such confusion and to unambiguously associate a meaning with the remaining flags, the following requirement is made:
This document changes Section 4 of [RFC3306] as follows:
OLD:
| 8 | 4 | 4 | 8 | 8 | 64 | 32 |
+--------+----+----+--------+--------+----------------+----------+
|11111111|flgs|scop|reserved| plen | network prefix | group ID |
+--------+----+----+--------+--------+----------------+----------+
+-+-+-+-+
flgs is a set of 4 flags: |0|0|P|T|
+-+-+-+-+
o P = 0 indicates a multicast address that is not assigned
based on the network prefix. This indicates a multicast
address as defined in [ADDRARCH].
o P = 1 indicates a multicast address that is assigned based
on the network prefix.
o If P = 1, T MUST be set to 1, otherwise the setting of the T
bit is defined in Section 2.7 of [ADDRARCH].
The reserved field MUST be zero.
NEW:
| 8 | 4 | 4 | 4 | 4 | 8 | 64 | 32 |
+--------+----+----+----+----+--------+----------------+----------+
|11111111|ff1 |scop|ff2 |rsvd| plen | network prefix | group ID |
+--------+----+----+----+----+--------+----------------+----------+
+-+-+-+-+
ff1 (flag field 1) is a set of 4 flags: |X|Y|P|T|
+-+-+-+-+
X and Y may each be set to 0 or 1. Note, X is for future assignment
while a meaning is associated with Y in RFC3956.
o P = 0 indicates a multicast address that is not assigned
based on the network prefix. This indicates a multicast
address as defined in [RFC4291].
o P = 1 indicates a multicast address that is assigned based
on the network prefix.
o If P = 1, T MUST be set to 1, otherwise the setting of the T
bit is defined in Section 2.7 of [RFC4291].
+-+-+-+-+
ff2 (flag field 2) is a set of 4 flags: |r|r|r|r|
+-+-+-+-+
where "rrrr" are for future assignment as additional flag bits.
r bits MUST each be sent as zero and MUST be ignored on receipt.
Flag bits denote both ff1 and ff2.
This document changes Section 6 of [RFC3306] as follows:
OLD:
NEW:
This document changes Section 2 of [RFC3956] as follows:
OLD:
As described in [RFC3306], the multicast address format is as
follows:
| 8 | 4 | 4 | 8 | 8 | 64 | 32 |
+--------+----+----+--------+----+----------------+----------+
|11111111|flgs|scop|reserved|plen| network prefix | group ID |
+--------+----+----+--------+----+----------------+----------+
Where flgs are "0011". (The first two bits are as yet undefined,
sent as zero and ignored on receipt.)
The multicast address format is as follows:
| 8 | 4 | 4 | 4 | 4 | 8 | 64 | 32 |
+--------+----+----+----+----+----+----------------+----------+
|11111111|ff1 |scop|ff2 |rsvd|plen| network prefix | group ID |
+--------+----+----+----+----+----+----------------+----------+
+-+-+-+-+
ff1 (flag field 1) is a set of four flags: |X|R|P|T|
+-+-+-+-+
where X is for future assignment as additional flag bit. X may be
set to 0 or 1.
+-+-+-+-+
ff2 (flag field 2) is a set of 4 flags: |r|r|r|r|
+-+-+-+-+
where "rrrr" are for future assignment as additional flag bits.
r bits MUST each be sent as zero and MUST be ignored on receipt.
Flag bits denote both ff1 and ff2.
This document changes Section 3 of [RFC3956] as follows:
OLD:
| 8 | 4 | 4 | 4 | 4 | 8 | 64 | 32 |
+--------+----+----+----+----+----+----------------+----------+
|11111111|flgs|scop|rsvd|RIID|plen| network prefix | group ID |
+--------+----+----+----+----+----+----------------+----------+
+-+-+-+-+
flgs is a set of four flags: |0|R|P|T|
+-+-+-+-+
When the highest-order bit is 0, R = 1 indicates a multicast address
that embeds the address on the RP. Then P MUST be set to 1, and
consequently T MUST be set to 1, as specified in [RFC3306]. In
effect, this implies the prefix FF70::/12. In this case, the last 4
bits of the previously reserved field are interpreted as embedding
the RP interface ID, as specified in this memo.
The behavior is unspecified if P or T is not set to 1, as then the
prefix would not be FF70::/12. Likewise, the encoding and the
protocol mode used when the two high-order bits in "flgs" are set to
11 ("FFF0::/12") is intentionally unspecified until such time that
the highest-order bit is defined. Without further IETF
specification, implementations SHOULD NOT treat the FFF0::/12 range
as Embedded-RP.
NEW:
| 8 | 4 | 4 | 4 | 4 | 8 | 64 | 32 |
+--------+----+----+----+----+----+----------------+----------+
|11111111|ff1 |scop|ff2 |RIID|plen| network prefix | group ID |
+--------+----+----+----+----+----+----------------+----------+
+-+-+-+-+
ff1 is a set of four flags: |X|R|P|T|
+-+-+-+-+
where X is for future assignment as additional flag bit. X may be
set to 0 or 1.
R = 1 indicates a multicast address that embeds the address of the
RP. Then P MUST be set to 1, and consequently T MUST be set to 1,
according to [RFC3306], as this is a special case of unicast-prefix
based addresses. This implies that, for instance, prefixes ff70::/12
and fff0::/12 are embedded RP prefixes. When the R-bit is set, the
last 4 bits of the field that were reserved in [RFC3306] are
interpreted as embedding the RP interface ID, as specified in this
memo.
This document changes Section 4 of [RFC3956] as follows:
OLD:
NEW:
This document changes Section 7.1 of [RFC3956] as follows:
OLD:
NEW:
This document does not require any action from IANA.
The same security considerations as those discussed in [RFC3956], [RFC3306] and [RFC4291] are to be taken into account.
Special thanks to Brian Haberman for the discussions prior to the publication of this document.
Many thanks to Jouni Korhonen, Tatuya Jinmei, Charlie Kaufman, and Ben Campbell for their review.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC3306] | Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 Multicast Addresses", RFC 3306, August 2002. |
| [RFC3956] | Savola, P. and B. Haberman, "Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address", RFC 3956, November 2004. |
| [RFC4291] | Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. |
| [RFC5952] | Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 Address Text Representation", RFC 5952, August 2010. |
| [I-D.ietf-mboned-64-multicast-address-format] | Boucadair, M., Qin, J., Lee, Y., Venaas, S., Li, X. and M. Xu, "IPv6 Multicast Address With Embedded IPv4 Multicast Address", Internet-Draft draft-ietf-mboned-64-multicast-address-format-05, April 2013. |