IDR J. Haas
Internet-Draft Juniper Networks
Intended status: Informational J. Mitchell
Expires: September 21, 2014 Microsoft Corporation
March 20, 2014
Reservation of Last Autonomous System (AS) Numbers
draft-ietf-idr-last-as-reservation-04
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 last 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
[RFC6996] ranges, they are not defined or reserved as Private Use
ASNs by [IANA.AS]. 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
A subset of the BGP communities of ASN 65535, the last ASN of the 16
bit range, are reserved for use by Well-known communities as
described in [RFC1997] and [IANA.WK]. Although this is not currently
true of ASN 4294967295, if there is a future need for another Special
Use ASN that is not designed to be globally routable, or the
associated BGP communities of such an ASN, ASN 4294967295 could be a
valid candidate for such purpose. This document does not prescribe
any such Special Use to this ASN at the time of publication.
4. Operational Considerations
Operators SHOULD NOT use these Last ASNs as if they are Private Use
ASNs or for any other purpose. Operational use of these Last ASNs
could have 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 undesireable routing
behavior.
These last ASNs MUST NOT be advertised to the global Internet within
AS_PATH or AS4_PATH attributes. Operators that choose to do
filtering of Private Use ASNs within the AS_PATH and AS4_PATH
attributes SHOULD also filter these Last ASNs.
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5. Implementation Considerations
While these Last ASNs are reserved, they remain valid ASNs from a BGP
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 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
[Note to IANA, TO BE REMOVED BEFORE PUBLICATION: IANA please update
the reservations for values 65535 and 4294967295 in the three
registries mentioned below to reference this document. Please note
at the time of this comment the "Special-Purpose AS Numbers registry"
has not yet been created but should be before publication of this
document.]
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 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].
This reservation has also been documented in the IANA Special-Purpose
AS Numbers Registry as described by [I-D.housley-number-registries].
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.
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8. References
8.1. Normative References
[I-D.housley-number-registries]
Housley, R., "Internet Numbers Registries", draft-housley-
number-registries-04 (work in progress), February 2014.
[IANA.AS] IANA, , "Autonomous System (AS) Numbers", March 2014,
.
[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.
[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
Autonomous System (AS) Number Space", RFC 6793, December
2012.
8.2. Informative References
[IANA.WK] IANA, , "Border Gateway Protocol (BGP) Well-known
Communities", March 2014, .
[RFC1997] Chandrasekeran, R., Traina, P., and T. Li, "BGP
Communities Attribute", RFC 1997, August 1996.
[RFC6996] Mitchell, J., "Autonomous System (AS) Reservation for
Private Use", BCP 6, RFC 6996, July 2013.
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
and David Farmer for his contributions to the document.
Authors' Addresses
Jeffrey Haas
Juniper Networks
Email: jhaas@juniper.net
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Jon Mitchell
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
USA
Email: Jon.Mitchell@microsoft.com
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