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INFORMATIONAL

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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   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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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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   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/








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