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: [email protected]


  Rishabh Parekh
  Cisco Systems
  Tasman Drive
  San Jose, CA  95134
  USA
  EMail: [email protected]


  Gunter Van de Velde
  Cisco Systems
  De Kleetlaan 6a
  Diegem  1831
  Belgium
  Phone: +32 476 476 022
  EMail: [email protected]


  Tim Chown
  University of Southampton
  Highfield
  Southampton, Hampshire  SO17 1BJ
  United Kingdom
  EMail: [email protected]


  Marshall Eubanks
  Iformata Communications
  130 W. Second Street
  Dayton, Ohio  45402
  US
  Phone: +1 703 501 4376
  EMail: [email protected]
  URI:   http://www.iformata.com/








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