| 6man Working Group | M. Boucadair |
| Internet-Draft | France Telecom |
| Updates: 3306,3956,4607,4291 (if approved) | S. Venaas |
| Intended status: Standards Track | Cisco |
| Expires: November 24, 2013 | May 23, 2013 |
Updates to the IPv6 Multicast Addressing Architecture
draft-ietf-6man-multicast-addr-arch-update-01
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, RFC 4607 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 Internet-Draft will expire on November 24, 2013.
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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 3.1) and also about IANA assigned SSM blocks (Section 3.2).
This document updates [RFC3956], [RFC3306], [RFC4607] and [RFC4291].
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|flgs|scop|flgs| group ID | +--------+----+----+----+-----------------------------------------+
Figure 1: Updated IPv6 Multicast Addressing Architecture
OLD (RFC3956): | 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|flgs|scop|flgs|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 recommendation is made
Another issue related to SSM is the IANA assigned SSM address block. Per [RFC4607], ff3x::4000:0001 through ff3x::7fff:fff is the block for IANA assignments (http://www.iana.org/assignments/ipv6-multicast-addresses/ipv6-multicast-addresses.xml). However, IANA assignments are permanent addresses and should not have the transient bit set. Quoting from [RFC4607]:
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 | 8 | 8 | 64 | 32 |
+--------+----+----+--------+--------+----------------+----------+
|11111111|flgs|scop|reserved| plen | network prefix | group ID |
+--------+----+----+--------+--------+----------------+----------+
+-+-+-+-+
flgs 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 [ADDRARCH].
o P = 1 indicates a multicast address that is assigned based
on the network prefix.
o T is set according to the definition in Section 2.7
of [ADDRARCH]. Unicast-Prefix-based addresses would
typically not be IANA assigned, so in most cases T would
be set to 1.
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.)
As described in [RFC3306], the multicast address format is as
follows:
| 8 | 4 | 4 | 4 | 4 | 8 | 64 | 32 |
+--------+----+----+---------+----+----------------+----------+
|11111111|flgs|scop|flgs|rsvd|plen| network prefix | group ID |
+--------+----+----+---------+----+----------------+----------+
+-+-+-+-+
flgs is a set of four flags: |X|R|P|T|
+-+-+-+-+
X may be set to 0 or 1.
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|flgs|scop|flgs|RIID|plen| network prefix | group ID |
+--------+----+----+----+----+----+----------------+----------+
+-+-+-+-+
flgs 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 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, but all multicast
addresses with the R-bit set to 1 MUST be treated as Embedded RP
addresses. The behavior is unspecified if P 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 changes the abstract of [RFC4607] as follows:
OLD:
NEW:
This document changes Section 1 of [RFC4607] as follows:
OLD:
NEW:
This document may require IANA updates. However, at this point it is not clear exactly what these updates may be.
Security considerations discussed in [RFC3956], [RFC3306], [RFC4607] and [RFC4291] MUST be taken into account.
Many thanks to B. Haberman for the discussions prior to the publication of this document.
| [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. |
| [RFC4607] | Holbrook, H. and B. Cain, "Source-Specific Multicast for IP", RFC 4607, August 2006. |
| [RFC4291] | Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006. |