Internet Engineering Task Force (IETF) S. Venaas
Request for Comments: 6676 R. Parekh
Category: Informational G. Van de Velde
ISSN: 2070-1721 Cisco Systems
T. Chown
University of Southampton
M. Eubanks
Iformata Communications
August 2012
Multicast Addresses for Documentation
Abstract
This document discusses which multicast addresses should be used for
documentation purposes and reserves multicast addresses for such use.
Some multicast addresses are derived from AS numbers or unicast
addresses. This document also explains how these can be used for
documentation purposes.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6676.
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Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................2
2. IPv4 Multicast Documentation Addresses ..........................3
2.1. Administratively Scoped IPv4 Multicast Addresses ...........3
2.2. GLOP Multicast Addresses ...................................3
2.3. Unicast Prefix-Based IPv4 Multicast Addresses ..............4
3. IPv6 Multicast Documentation Addresses ..........................4
3.1. Unicast Prefix-Based IPv6 Multicast Addresses ..............5
3.2. Embedded-RP IPv6 Multicast Addresses .......................5
4. Security Considerations .........................................5
5. IANA Considerations .............................................5
6. Acknowledgments .................................................6
7. Informative References ..........................................6
1. Introduction
It is often useful in documentation, IETF documents, etc., to provide
examples containing IP multicast addresses. For documentation where
examples of general purpose multicast addresses are needed, one
should use multicast addresses that will never be assigned or in
actual use. There is a risk that addresses used in examples may
accidentally be used. It is then important that the same addresses
not be used by other multicast applications or services. It may also
be beneficial to filter out such addresses from multicast signalling
and to filter out multicast data sent to such addresses.
For unicast, there are both IPv4 and IPv6 addresses reserved for this
purpose; see [RFC5737] and [RFC3849], respectively. This document
reserves multicast addresses for this same purpose.
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There are also some multicast addresses that are derived from AS
numbers or unicast addresses. For examples where such addresses are
desired, one should derive them from the AS numbers and unicast
addresses reserved for documentation purposes. This document also
discusses the use of these.
2. IPv4 Multicast Documentation Addresses
For Any-Source Multicast (ASM), the IPv4 multicast addresses
allocated for documentation purposes are 233.252.0.0 - 233.252.0.255
(233.252.0.0/24).
For Source-Specific Multicast (SSM), it is less important which
multicast addresses are used, since a host/application joins a
channel identified by both source and group. Any source addresses
used in SSM examples should be unicast addresses reserved for
documentation purposes. There are three unicast address ranges
provided for documentation use in [RFC5737]. The ranges are
192.0.2.0/24, 198.51.100.0/24 and 203.0.113.0/24.
Sometimes one wants to give examples where a specific type of address
is desired. For example, for text about multicast scoping, one might
want the examples to use addresses that are to be used for
administrative scoping. See below for guidance on how to construct
specific types of example addresses.
2.1. Administratively Scoped IPv4 Multicast Addresses
Administratively scoped IPv4 multicast addresses [RFC2365] are
reserved for scoped multicast. They can be used within a site or an
organization. Apart from a small set of scope-relative addresses,
these addresses are not assigned. The high order /24 in every scope
is reserved for relative assignments. A relative assignment is an
integer offset from the highest address in the scope and represents
an IPv4 address. For documentation purposes, the integer offset is
10. This provides one multicast address per scope.
For example in the Local Scope 239.255.0.0/16, the multicast address
for documentation purposes is 239.255.255.245.
2.2. GLOP Multicast Addresses
GLOP [RFC3180] is a method for deriving IPv4 multicast group
addresses from 16-bit AS numbers. For examples where GLOP addresses
are desired, the addresses should be derived from the AS numbers
reserved for documentation use.
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RFC 6676 Multicast Addresses for Documentation August 2012
The 16-bit AS numbers reserved for documentation use in [RFC5398] are
64496 - 64511. By use of [RFC3180], we then get 16 /24 multicast
prefixes for documentation use. The first one is 233.251.240.0/24,
and the last one is 233.251.255.0/24.
2.3. Unicast Prefix-Based IPv4 Multicast Addresses
IPv4 multicast addresses can be derived from IPv4 unicast prefixes,
see [RFC6034]. For examples where this type of address is desired,
the addresses should be derived from the unicast addresses reserved
for documentation purposes, see [RFC5737].
There are three unicast address ranges provided for documentation use
in [RFC5737]. The ranges are 192.0.2.0/24, 198.51.100.0/24, and
203.0.113.0/24. Using [RFC6034], this leaves the unicast prefix-
based IPv4 multicast addresses 234.192.0.2, 234.198.51.100, and
234.203.0.113.
3. IPv6 Multicast Documentation Addresses
For Any-Source Multicast (ASM), the IPv6 multicast addresses
allocated for documentation purposes are FF0X::DB8:0:0/96. This is a
/96 prefix so that it can be used with group IDs, according to the
allocation guidelines in [RFC3307]. Also note that for these
addresses, the transient flag, or "T-flag" as defined in [RFC4291],
is zero. This is because they are permanently assigned. There can
be no permanently assigned addresses for documentation purposes with
the transient flag set to one, since the flag set to one means that
they are not permanently assigned.
For Source-Specific Multicast (SSM), it is less important which
multicast addresses are used, since a host/application joins a
channel identified by both source and group. Any source addresses
used in SSM examples should be unicast addresses reserved for
documentation purposes. The IPv6 unicast prefix reserved for
documentation purposes is 2001:DB8::/32, see [RFC3849].
Sometimes one wants to give examples where a specific type of address
is desired. For example, for text about multicast scoping, one might
want the examples to use addresses that are to be used for
administrative scoping. See below for guidance on how to construct
specific types of example addresses.
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RFC 6676 Multicast Addresses for Documentation August 2012
3.1. Unicast Prefix-Based IPv6 Multicast Addresses
IPv6 multicast addresses can be derived from IPv6 unicast prefixes,
see [RFC3306]. For examples where this type of address is desired,
the addresses should be derived from the unicast addresses reserved
for documentation purposes.
The IPv6 unicast prefix reserved for documentation purposes is 2001:
DB8::/32, see [RFC3849]. This allows a wide range of different IPv6
multicast addresses. Using just the base /32 prefix, one gets the
IPv6 multicast prefixes FF3X:20:2001:DB8::/64 -- one for each
available scope X. One can also produce longer prefixes from this.
Just as an example, one can pick a /64 prefix 2001:DB8:DEAD:
BEEF::/64, which gives the multicast prefixes FF3X:40:2001:DB8:DEAD:
BEEF::/96 -- one for each available scope X.
3.2. Embedded-RP IPv6 Multicast Addresses
There is a type of IPv6 multicast address called an "Embedded-RP"
address, where the IPv6 address of a Rendezvous-Point (RP) is
embedded inside the multicast address, see [RFC3956]. For examples
where this type of address is desired, the addresses should be
derived from the unicast addresses reserved for documentation
purposes, see [RFC3849].
For documentation purposes, the RP address can be any address from
the range 2001:DB8::/32 that follows the constraints specified in
[RFC3956]. One example address could be 2001:DB8::1. The
Embedded-RP multicast prefixes might then be FF7X:120:2001:DB8::/96.
Another example could be the RP address 2001:DB8:BEEF:FEED::7, which
gives the prefixes FF7X:740:2001:DB8:BEEF:FEED::/96. See also the
examples in [RFC3956].
4. Security Considerations
The use of specific multicast addresses for documentation purposes
has no negative impact on security.
5. IANA Considerations
IANA has added a reference to this document for the IPv4 MCAST-TEST-
NET allocation so that all the different documentation multicast
assignments reference this document.
IANA has assigned a scope-relative IPv4 address for documentation
purposes.
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RFC 6676 Multicast Addresses for Documentation August 2012
IANA has assigned "variable-scope" IPv6 multicast addresses for
documentation purposes. This is a /96 prefix.
6. Acknowledgments
The authors thank Roberta Maglione, Leonard Giuliano and Dave Thaler
for providing comments on this document.
7. Informative References
[RFC2365] Meyer, D., "Administratively Scoped IP Multicast", BCP 23,
RFC 2365, July 1998.
[RFC3180] Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8",
BCP 53, RFC 3180, September 2001.
[RFC3306] Haberman, B. and D. Thaler, "Unicast-Prefix-based IPv6
Multicast Addresses", RFC 3306, August 2002.
[RFC3307] Haberman, B., "Allocation Guidelines for IPv6 Multicast
Addresses", RFC 3307, August 2002.
[RFC3849] Huston, G., Lord, A., and P. Smith, "IPv6 Address Prefix
Reserved for Documentation", RFC 3849, July 2004.
[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.
[RFC5398] Huston, G., "Autonomous System (AS) Number Reservation for
Documentation Use", RFC 5398, December 2008.
[RFC5737] Arkko, J., Cotton, M., and L. Vegoda, "IPv4 Address Blocks
Reserved for Documentation", RFC 5737, January 2010.
[RFC6034] Thaler, D., "Unicast-Prefix-Based IPv4 Multicast
Addresses", RFC 6034, October 2010.
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Authors' Addresses
Stig Venaas
Cisco Systems
Tasman Drive
San Jose, CA 95134
USA
EMail: stig@cisco.com
Rishabh Parekh
Cisco Systems
Tasman Drive
San Jose, CA 95134
USA
EMail: riparekh@cisco.com
Gunter Van de Velde
Cisco Systems
De Kleetlaan 6a
Diegem 1831
Belgium
Phone: +32 476 476 022
EMail: gvandeve@cisco.com
Tim Chown
University of Southampton
Highfield
Southampton, Hampshire SO17 1BJ
United Kingdom
EMail: tjc@ecs.soton.ac.uk
Marshall Eubanks
Iformata Communications
130 W. Second Street
Dayton, Ohio 45402
US
Phone: +1 703 501 4376
EMail: marshall.eubanks@iformata.com
URI: http://www.iformata.com/
Venaas, et al. Informational [Page 7]
