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 (C) The Internet Society (2001). All Rights Reserved.
This document defines the policy for the use of 233/8 for statically
assigned multicast addresses.
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 |
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.
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
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
Meyer & Lothberg Best Current Practice [Page 2]RFC 3180 GLOP Addressing in 233/8 September 20016. 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.
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