Internet DRAFT - draft-jhjm-idr-last-as-reservations
draft-jhjm-idr-last-as-reservations
Network Working Group J. Haas
Internet-Draft Juniper Networks
Intended status: Informational J. Mitchell
Expires: November 17, 2013 Microsoft Corporation
May 16, 2013
Last Autonomous System (AS) Reservations
draft-jhjm-idr-last-as-reservations-00
Abstract
This document reserves two Autonomous System numbers (ASNs) at the
end of the 16 bit and 32 bit ranges, described in this document as
"Last ASNs" and recommends they not be used by operators.
Status of This Memo
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This Internet-Draft will expire on November 17, 2013.
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1. Introduction
IANA has reserved the last Autonomous System Number (ASN), 65535, of
the 16 bit autonomous system number range for over a decade with the
intention that it not be used by BGP [RFC4271] network operators.
Since the introduction of BGP Support for Four-Octet AS Number Space
[RFC6793], IANA has also reserved the ASN of the 32 bit autonomous
system number range, 4294967295. These reservations have been
documented in the IANA Autonomous System Numbers Registry [IANA.AS].
Although these "Last ASNs" border on Private Use ASN ranges, they are
not defined as Private Use ASNs by
[I-D.ietf-idr-as-private-reservation]. This document describes the
reasoning for these reservations and provides guidance both to
operators and to authors of future protocol enhancements on their
use.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3. Reasons for Last ASN Reservations
The primary reason for reserving the Last ASNs of the 16 bit and 32
bit ASN ranges is that these numbers are also at the end of typical
computational data structures holding the underlying number.
Programmatic errors are more common when handling of end of range
values, and sometimes last values (binary all ones) have been used as
"magic numbers", to represent a different number or behavior.
Secondly, a subset of the standard BGP communities of the last ASN of
the 16 bit range, 65535, are reserved for use by Well-known
communities as described in RFC 1997 [RFC1997] and IANA [IANA.WK].
Although this not currently true of ASN 4294967295, if there is a
future need for a Special Use ASN that is not designed to be globally
routable, or the associated BGP attributes (such as communities) of
such an ASN, this may be a valid candidate for such purpose. This
document does not prescribe any such purpose to this ASN.
4. Operational Considerations
Operators MUST NOT use Last ASNs as if they are Private Use ASNs, or
for any other purpose, since they are reserved and implementations
may have errors in regards to handling these ASNs. Implementations
SHOULD NOT handle Last ASNs in the same fashion as Private Use ASNs.
Operators are accustomed to being able to fully utilize the
communities associated with the ASN's they have deployed utilizing
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the format described in RFC 1997 [RFC1997], even in the case of
Private Use ASNs. In the case of usage of ASN 65535 as if it was a
Private Use ASN, operators might not recognize these communities are
reserved as BGP Well-known community values [IANA.WK], causing
undesirable routing behavior if prefixes are tagged with such
communities within the network.
Operators that choose to filter or provide tools that filter AS_PATH,
MAY choose to filter Last ASNs in the same way as Private Use ASNs,
to prevent the use of these reserved ASNs on their networks.
5. Acknowledgements
The author would like to thank Michelle Cotton and Elwyn Davis for
encouraging the proper documentation of the reservation of these
ASNs.
6. IANA Considerations
IANA has reserved Autonomous System number 65535 from the "16-bit
Autonomous System Numbers" registry for the reasons described in this
document.
IANA has also reserved Autonomous System number 4294967295 from the
"32-bit Autonomous System Numbers" registry for the reasons described
in this document.
These reservations have been documented in the IANA Autonomous System
Numbers Registry [IANA.AS].
7. Security Considerations
This document does not introduce any additional security concerns in
regards to the Last ASNs usage. Although the BGP protocol is
designed to allow usage of these Last ASNs, security issues related
to BGP implementation errors may be triggered by Last ASN usage.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
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[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
Autonomous System (AS) Number Space", RFC 6793, December
2012.
8.2. Informative References
[I-D.ietf-idr-as-private-reservation]
Mitchell, J., "Autonomous System (AS) Reservation for
Private Use", draft-ietf-idr-as-private-reservation-04
(work in progress), April 2013.
[IANA.AS] IANA, "Autonomous System (AS) Numbers", May 2013,
<http://www.iana.org/assignments/as-numbers/>.
[IANA.WK] IANA, "Border Gateway Protocol (BGP) Well-known
Communities", May 2013, <http://www.iana.org/assignments/
bgp-well-known-communities/>.
[RFC1997] Chandrasekeran, R., Traina, P., and T. Li, "BGP
Communities Attribute", RFC 1997, August 1996.
Authors' Addresses
Jeffrey Haas
Juniper Networks
Email: jhaas@juniper.net
Jon Mitchell
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
USA
Email: Jon.Mitchell@microsoft.com
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