IDR J. Haas
Internet-Draft Juniper Networks
Intended status: Informational J. Mitchell
Expires: January 16, 2014 Microsoft Corporation
July 15, 2013
Reservation of Last Autonomous System (AS) Numbers
draft-ietf-idr-last-as-reservation-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 provides guidance to implementers and operators on
their use.
Status of This Memo
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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 network operators running BGP
[RFC4271]. 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. This reservation has
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 reserving these Last ASNs and provides guidance both to
operators and to implementers 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 ASNs Reservation
The primary reason for reserving the Last ASN of both 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 [RFC1997] and [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
could 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 these Last ASNs as if they are Private Use
ASNs, and SHOULD NOT use these Last ASNs for any other purpose,
except a Special Uses defined elsewhere. Any other operational use
of these Last ASNs could have unpredictable or undesirable results.
For example; use of AS 65535 as if it were a Private Use ASN, may
result in inadvertent use of BGP Well-known community values
[IANA.WK], causing undesired routing behavior.
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Operators that choose to filter Private Use ASNs within the AS_PATH
and AS4_PATH attributes SHOULD also filter these Last ASNs. These
last ASNs MUST NOT be advertised to the global Internet within
AS_PATH or AS4_PATH attributes.
5. Implementation Considerations
While these Last ASNs are reserved, they remain valid ASNs from a
protocol perspective. Therefore, implementations of BGP [RFC4271]
SHOULD NOT treat the use of these Last ASNs as any type of protocol
error. However, implementations MAY generate a local warning message
indicating probable improper use of a reserved ASN.
Implementations that provide tools that filter Private Use ASNs
within the AS_PATH and AS4_PATH attributes MAY also include these
Last ASNs.
6. IANA Considerations
IANA has reserved last Autonomous System number 65535 from the
"16-bit Autonomous System Numbers" registry for the reasons described
in this document.
IANA has also reserved last Autonomous System number 4294967295 from
the "32-bit Autonomous System Numbers" registry for the reasons
described in this document.
This reservation has 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 usage of Last ASNs. Although the BGP protocol is designed
to allow usage of these Last ASNs, security issues related to BGP
implementation errors could be triggered by Last ASN usage.
8. References
8.1. Normative References
[IANA.AS] IANA, ., "Autonomous System (AS) Numbers", July 2013,
.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[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-05
(work in progress), May 2013.
[IANA.WK] IANA, ., "Border Gateway Protocol (BGP) Well-known
Communities", July 2013, .
[RFC1997] Chandrasekeran, R., Traina, P., and T. Li, "BGP
Communities Attribute", RFC 1997, August 1996.
Appendix A. Acknowledgements
The authors would like to thank Michelle Cotton and Elwyn Davis for
encouraging the proper documentation of the reservation of these
ASNs. The authors would also like to thank David Farmer for his
contributions to the document.
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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