GLOP Addressing in 233/8
RFC 3180

Document Type RFC - Best Current Practice (September 2001; Errata)
Obsoletes RFC 2770
Also known as BCP 53
Authors Peter Lothberg  , David Meyer 
Last updated 2020-01-21
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Network Working Group                                           D. Meyer
Request for Comments: 3180                                   P. Lothberg
Obsoletes: 2770                                                   Sprint
BCP: 53                                                   September 2001
Category: Best Current Practice

                        GLOP Addressing in 233/8

Status of this Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2001).  All Rights Reserved.


   This document defines the policy for the use of 233/8 for statically
   assigned multicast addresses.

1. Introduction

   It is envisioned that the primary use of this space will be many-to-
   many applications.  This allocation is in addition to those described
   on [IANA] (e.g., [RFC2365]).  The IANA has allocated 223/8 as per RFC
   2770 [RFC2770].  This document obsoletes RFC 2770.

2. Problem Statement

   Multicast addresses have traditionally been allocated by a dynamic
   mechanism such as SDR [RFC2974].  However, many current multicast
   deployment models are not amenable to dynamic allocation.  For
   example, many content aggregators require group addresses that are
   fixed on a time scale that is not amenable to allocation by a
   mechanism such as described in [RFC2974].  Perhaps more seriously,
   since there is not general consensus by providers, content
   aggregators, or application writers as to the allocation mechanism,
   the Internet is left without a coherent multicast address allocation

Meyer & Lothberg         Best Current Practice                  [Page 1]
RFC 3180                GLOP Addressing in 233/8          September 2001

   The MALLOC working group has created a specific strategy for global
   multicast address allocation [RFC2730, RFC2909].  However, this
   approach has not been widely implemented or deployed.  This document
   proposes a solution for a subset of the problem, namely, those cases
   not covered by Source Specific Multicast.

3. Address Space

   The IANA has allocated 223/8 as per RFC 2770 [RFC2770].  RFC 2770
   describes the administration of the middle two octets of 233/8 in a
   manner similar to that described in RFC 1797:

       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      |      233      |           16 bits AS          |  local bits   |

3.1. Example

   Consider, for example, AS 5662.  Written in binary, left padded with
   0s, we get 0001011000011110.  Mapping the high order octet to the
   second octet of the address, and the low order octet to the third
   octet, we get 233.22.30/24.

4. Allocation

   As mentioned above, the allocation proposed here follows the RFC 1797
   (case 1) allocation scheme, modified as follows: the high-order octet
   has the value 233, and the next 16 bits are a previously assigned
   Autonomous System number (AS), as registered by a network registry
   and listed in the RWhois database system.  This allows a single /24
   per AS.

   As was the case with RFC 1797, using the AS number in this way allows
   automatic assignment of a single /24 to each service provider and
   does not require an additional registration step.

4.1. Private AS Space

   The part of 233/8 that is mapped to the private AS space [RFC1930] is
   assigned to the IRRs [RFC3138].

5. Large AS Numbers

   It is important to note that this approach will work only for two
   octet AS numbers.  In particular, it does not work for any AS number
   extension scheme.

Meyer & Lothberg         Best Current Practice                  [Page 2]
RFC 3180                GLOP Addressing in 233/8          September 2001

6. Security Considerations

   The approach described here may have the effect of reduced exposure
   to denial-of-service attacks based on dynamic allocation.  Further,
   since dynamic assignment does not cross domain boundaries, well-known
   intra-domain security techniques can be applied.

7. IANA Considerations

   The IANA has assigned 233/8 for this purpose.

8. Acknowledgments

   This proposal originated with Peter Lothberg's idea that we use the
   same allocation (AS based) as described in RFC 1797.  Randy Bush and
   Mark Handley contributed many insightful comments, and Pete and
   Natalie Whiting contributed greatly to the readability of this

9. References


   [RFC1797] IANA, "Class A Subnet Experiment", RFC 1797, April 1995.

   [RFC1930] Hawkinson, J. and T. Bates,  "Guidelines for creation,
             selection, and registration of an Autonomous System (AS)",
             RFC 1930, March 1996.
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