| 6man Working Group | M. Boucadair |
| Internet-Draft | France Telecom |
| Updates: 3306,3956,4291 (if approved) | S. Venaas |
| Intended status: Standards Track | Cisco |
| Expires: August 17, 2014 | February 13, 2014 |
Updates to the IPv6 Multicast Addressing Architecture
draft-ietf-6man-multicast-addr-arch-update-03
This document updates the IPv6 multicast addressing architecture by defining the 17-20 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 multicast addressing architecture [RFC4291] by defining the 17-20 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 recommendation on the flag bits (Section 3).
Textual representation of IPv6 addresses included in the RFC updates follows the recommendation in [RFC5952].
Bits 17-20 of a multicast address 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. Figure 1 and Figure 2 show the updated structure of the addressing architecture. The first diagram shows the update of the base IPv6 addressing architecture, and the second shows the update of so-called Embedded-RP.
OLD:
| 8 | 4 | 4 | 112 bits |
+--------+----+----+----------------------------------------------+
|11111111|flgs|scop| group ID |
+--------+----+----+----------------------------------------------+
NEW:
| 8 | 4 | 4 | 4 | 108 bits |
+--------+----+----+----------------------------------------------+
|11111111|ff1 |scop|ff2 | group ID |
+--------+----+----+----+-----------------------------------------+
* ff1 refers to "flag field 1"
* ff2 refers to "flag field 2"
* flag bits denote both ff1 and ff2.
Figure 1: Updated IPv6 Multicast Addressing Architecture
OLD (RFC 3956): | 8 | 4 | 4 | 4 | 4 | 8 | 64 | 32 | +--------+----+----+----+----+--------+----------------+----------+ |11111111|flgs|scop|rsvd|RIID| plen | network prefix | group ID | +--------+----+----+----+----+--------+----------------+----------+ NEW: | 8 | 4 | 4 | 4 | 4 | 8 | 64 | 32 | +--------+----+----+----+----+--------+----------------+----------+ |11111111|ff1 |scop|ff2 |RIID| plen | network prefix | group ID | +--------+----+----+----+----+--------+----------------+----------+
Figure 2: Embedded-RP with Updated IPv6 Multicast Address Arch.
Further specification documents may define a meaning for these flag bits. 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.
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.
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.
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|
+-+-+-+-+
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.
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|
+-+-+-+-+
X may be set to 0 or 1.
R = 1 indicates a multicast address that embeds the address of the RP.
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.
The behavior is unspecified if P or T is not set to 1. When the
R-bit is set, the last 4 bits of the previously reserved field 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.
Security considerations discussed in [RFC3956], [RFC3306] and [RFC4291] MUST be taken into account.
Special thanks to B. Haberman for the discussions prior to the publication of this document.
Many thanks to J. Korhonen and T. Jinmei their comments.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC3956] | Savola, P. and B. Haberman, "Embedding the Rendezvous Point (RP) Address in an IPv6 Multicast Address", RFC 3956, November 2004. |
| [RFC3306] | Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6 Multicast Addresses", RFC 3306, August 2002. |
| [RFC5952] | Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 Address Text Representation", RFC 5952, August 2010. |
| [RFC4291] | Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. |