Multicast Doc Addresses: Multicast Addresses for Documentation
Reserved multicast addresses and schemes for use in documentation and examples.
Venaas, S., Parekh, R., Van de Velde, G., Chown, T., and M. Eubanks, "Multicast Addresses for Documentation", RFC 6676, DOI 10.17487/RFC6676, August 2012, <https://www.rfc-editor.org/info/rfc6676>.
@misc{rfc6676,
series = {Request for Comments},
number = 6676,
howpublished = {RFC 6676},
publisher = {RFC Editor},
doi = {10.17487/RFC6676},
url = {https://www.rfc-editor.org/info/rfc6676},
author = {S. Venaas and R. Parekh and G. Van de Velde and T. Chown and M. Eubanks},
title = {{Multicast Addresses for Documentation}},
pagetotal = 7,
year = 2012,
month = aug,
} RFC text
Contents
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.
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.
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.
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.
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.
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.
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/
AI ELI5
On this page
§1Introduction
When writing technical documentation and IETF specifications, examples often need to include multicast addresses. Without reserved addresses for this purpose, example code could accidentally send traffic to real multicast groups in use on production networks. This RFC reserves specific multicast address ranges for documentation only, similar to how RFC 5737 reserves unicast addresses like 192.0.2.0/24 and RFC 3849 reserves 2001:DB8::/32 for documentation.
The document defines both direct address reservations and guidance on deriving documentation addresses from reserved unicast prefixes and AS numbers, so that examples can use consistent addressing schemes without risk.
Just like books print fake phone numbers starting with 555 so real people don't get random calls, this RFC picks special network addresses that documentation can use without accidentally affecting real networks.
§2IPv4 Documentation Multicast Addresses
For IPv4, the reserved multicast addresses for documentation are 233.252.0.0/24. This block is reserved for Any-Source Multicast (ASM) examples, where any source can send to the group.
For Source-Specific Multicast (SSM) examples, writers should use the documentation unicast addresses from RFC 5737 (192.0.2.0/24, 198.51.100.0/24, and 203.0.113.0/24) as the source addresses. The RFC also provides guidance on deriving addresses using two additional methods: Administratively Scoped multicast addresses (using offset 10 within reserved scopes) and GLOP addresses derived from the reserved AS numbers 64496–64511, which produce the prefixes 233.251.240.0/24 through 233.251.255.0/24.
IPv4 has one block of fake multicast addresses (233.252.0.0/24) that's always safe to use in examples. For other methods, you can build them from the fake unicast addresses or fake AS numbers reserved for documentation.
§3IPv6 Documentation Multicast Addresses
For IPv6, the reserved multicast addresses for documentation are FF0X::DB8:0:0/96. This is a /96 prefix that allows use with different scope values (represented by the X). The addresses are marked as permanently assigned (T-flag is zero), making them suitable for stable documentation examples.
For Source-Specific Multicast (SSM) examples, writers should use the reserved IPv6 unicast prefix 2001:DB8::/32 as the source addresses. The RFC explains how to derive Unicast Prefix-Based IPv6 multicast addresses from this documentation prefix and how to create Embedded-RP addresses where the Rendezvous Point IPv6 address is embedded inside the multicast group address.
IPv6 has a similar block of fake multicast addresses (starting with FF0X::DB8) for documentation. You can also build examples using the fake IPv6 address prefix 2001:DB8, which is well known as a documentation placeholder.
§4Deployment and Operational Considerations
The RFC recommends that network operators filter out multicast traffic destined to these documentation addresses to further reduce any risk of accidental impact. Tools that process multicast signalling can also be configured to filter and discard signalling packets for these reserved addresses. This defense-in-depth approach ensures that even if example code escapes into production, these addresses will not be assigned or used by actual services.
The use of these reserved addresses has no negative impact on network security; instead, the practice improves operational safety by preventing documentation examples from interfering with real multicast traffic.
Networks can also filter out these fake addresses at the borders, so even if example code somehow runs on a real network, the fake addresses won't cause problems.