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.
Venaas, et al. Informational [Page 1]
RFC 6676 Multicast Addresses for Documentation August 2012
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.
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.
Venaas, et al. Informational [Page 2]
RFC 6676 Multicast Addresses for Documentation August 2012
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.
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.
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.
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.
Venaas, et al. Informational [Page 3]
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.
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.
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.
Venaas, et al. Informational [Page 4]
RFC 6676 Multicast Addresses for Documentation August 2012
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.
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].
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.
Venaas, et al. Informational [Page 5]
RFC 6676 Multicast Addresses for Documentation August 2012
IANA has assigned "variable-scope" IPv6 multicast addresses for documentation purposes. This is a /96 prefix.