RFC 3180 BEST CURRENT PRACTICE MULTICAST · ADDRESSING
GLOP Addressing in 233/8
Divides the 233/8 multicast block into fixed allocations based on two-octet AS numbers.
RFC EDITOR
Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8", BCP 53, RFC 3180, DOI 10.17487/RFC3180, September 2001, <https://www.rfc-editor.org/info/rfc3180>.
BIBTEX
@misc{rfc3180,
series = {Request for Comments},
number = 3180,
howpublished = {RFC 3180},
publisher = {RFC Editor},
doi = {10.17487/RFC3180},
url = {https://www.rfc-editor.org/info/rfc3180},
author = {D. Meyer and P. Lothberg},
title = {{GLOP Addressing in 233/8}},
pagetotal = 5,
year = 2001,
month = sep,
} LINEAGE · FROM THE RFC INDEXOpen full graph →
RFC text
Contents
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.
Abstract
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
scheme.
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.
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
document.
9. References
[IANA] http://www.iana.org/numbers.html
[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.
[RFC2365] Meyer, D., "Administratively Scoped IP Multicast", RFC
2365, July 1998.
[RFC2374] Hinden, R., O'Dell, M. and S. Deering, "An IPv6
Aggregatable Global Unicast Address Format", RFC 2374, July
1998.
[RFC2730] Hanna, S., Patel, B. and M. Shah, "Multicast Address
Dynamic Client Allocation Protocol (MADCAP)", RFC 2730,
December 1999.
[RFC2770] Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8", RFC
2770, February 2000.
[RFC2909] Radoslavov, P., Estrin, D., Govindan, R., Handley, M.,
Kumar, S. and D. Thaler, "The Multicast Address-Set Claim
(MASC) Protocol", RFC 2909, September 2000.
[RFC2974] Handley, M., Perkins, C. and E. Whelan, "Session
Announcement Protocol", RFC 2974, October 2000.
[RFC3138] Meyer, D., "Extended Assignments in 233/8", RFC 3138, June
2001.
10. Authors' Addresses
David Meyer
Sprint
VARESA0104
12502 Sunrise Valley Drive
Reston VA, 20196
EMail: dmm@sprint.net
Peter Lothberg
Sprint
VARESA0104
12502 Sunrise Valley Drive
Reston VA, 20196
EMail: roll@sprint.net
11. Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
ISO Plain Language
On this page
PROBLEMSome multicast applications need group addresses that remain fixed, but dynamic allocation does not meet every deployment's needs and there was no broadly agreed allocation scheme.
MECHANISMThe first octet is 233, the next 16 bits hold an assigned Autonomous System number, and the remaining 8 bits are local, providing one /24 per AS.
THE LIMITThe RFC defines an automatic allocation scheme for two-octet AS numbers and obsoletes RFC 2770. It does not work with extended AS numbers.
§2Why Fixed Multicast Addresses
Multicast addresses were often allocated dynamically, but some applications need addresses that stay fixed for longer periods. The memo gives content aggregators as an example and notes that the community lacked a coherent allocation scheme.
This approach addresses a subset of multicast allocation needs, specifically cases not covered by Source Specific Multicast.
Some applications need multicast addresses that stay the same rather than being assigned dynamically. This memo defines one way to allocate fixed addresses.
§3How the 233/8 Block Is Divided
The high-order octet is 233, the next 16 bits contain an already assigned Autonomous System (AS) number, and the last 8 bits are for local use. This gives each AS one /24 block.
For example, the RFC shows AS 5662 mapping to 233.22.30/24. Using the assigned AS number means the allocation is automatic and requires no additional registration step.
The address includes a network's AS number, followed by bits it can use locally. This lets the network determine its own block without a separate registration.
§5The Two-Octet AS Limit
The scheme works only with two-octet AS numbers. It cannot represent an AS number extension because the address has only 16 bits available for the AS number.
The address leaves 16 bits for the AS number. A longer AS number does not fit in this format.
§6Security and Allocation Notes
The memo says this approach may reduce exposure to denial-of-service attacks based on dynamic allocation. Because dynamic assignment does not cross domain boundaries in this scheme, familiar within-domain security techniques can be used.
IANA assigned 233/8 for this purpose. RFC 3180 obsoletes RFC 2770.
The memo notes that fixed allocation may reduce some risks tied to dynamic assignment. It also records the block's assignment and replaces the earlier RFC 2770 description.
§5References
[RFC1797]RFC 1797IANA, "Class A Subnet Experiment", RFC 1797, April 1995.April 1995[RFC1930]RFC 1930Hawkinson, J. and T. Bates, "Guidelines for creation, selection, and registration of an Autonomous System (AS)", RFC 1930, March 1996.March 1996[RFC2770]RFC 2770Meyer, D. and P. Lothberg, "GLOP Addressing in 233/8", RFC 2770, February 2000.February 2000[RFC2974]RFC 2974Handley, M., Perkins, C. and E. Whelan, "Session Announcement Protocol", RFC 2974, October 2000.October 2000