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2 IDR J. Haas
3 Internet-Draft Juniper Networks
4 Intended status: Informational J. Mitchell
5 Expires: January 16, 2014 Microsoft Corporation
6 July 15, 2013
8 Reservation of Last Autonomous System (AS) Numbers
9 draft-ietf-idr-last-as-reservation-00
11 Abstract
13 This document reserves two Autonomous System numbers (ASNs) at the
14 end of the 16 bit and 32 bit ranges, described in this document as
15 "Last ASNs" and provides guidance to implementers and operators on
16 their use.
18 Status of This Memo
20 This Internet-Draft is submitted in full conformance with the
21 provisions of BCP 78 and BCP 79.
23 Internet-Drafts are working documents of the Internet Engineering
24 Task Force (IETF). Note that other groups may also distribute
25 working documents as Internet-Drafts. The list of current Internet-
26 Drafts is at http://datatracker.ietf.org/drafts/current/.
28 Internet-Drafts are draft documents valid for a maximum of six months
29 and may be updated, replaced, or obsoleted by other documents at any
30 time. It is inappropriate to use Internet-Drafts as reference
31 material or to cite them other than as "work in progress."
33 This Internet-Draft will expire on January 16, 2014.
35 Copyright Notice
37 Copyright (c) 2013 IETF Trust and the persons identified as the
38 document authors. All rights reserved.
40 This document is subject to BCP 78 and the IETF Trust's Legal
41 Provisions Relating to IETF Documents
42 (http://trustee.ietf.org/license-info) in effect on the date of
43 publication of this document. Please review these documents
44 carefully, as they describe your rights and restrictions with respect
45 to this document. Code Components extracted from this document must
46 include Simplified BSD License text as described in Section 4.e of
47 the Trust Legal Provisions and are provided without warranty as
48 described in the Simplified BSD License.
50 1. Introduction
52 IANA has reserved the last Autonomous System Number (ASN), 65535, of
53 the 16 bit autonomous system number range for over a decade with the
54 intention that it not be used by network operators running BGP
55 [RFC4271]. Since the introduction of BGP Support for Four-Octet AS
56 Number Space [RFC6793], IANA has also reserved the ASN of the 32 bit
57 autonomous system number range, 4294967295. This reservation has
58 been documented in the IANA Autonomous System Numbers Registry
59 [IANA.AS]. Although these "Last ASNs" border on Private Use ASN
60 ranges, they are not defined as Private Use ASNs by
61 [I-D.ietf-idr-as-private-reservation]. This document describes the
62 reasoning for reserving these Last ASNs and provides guidance both to
63 operators and to implementers on their use.
65 2. Requirements Language
67 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
68 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
69 document are to be interpreted as described in RFC 2119 [RFC2119].
71 3. Reasons for Last ASNs Reservation
73 The primary reason for reserving the Last ASN of both the 16 bit and
74 32 bit ASN ranges is that these numbers are also at the end of
75 typical computational data structures holding the underlying number.
76 Programmatic errors are more common when handling of end of range
77 values, and sometimes last values (binary all ones) have been used as
78 "magic numbers", to represent a different number or behavior.
80 Secondly, a subset of the standard BGP communities of the last ASN of
81 the 16 bit range, 65535, are reserved for use by Well-known
82 communities as described in [RFC1997] and [IANA.WK]. Although this
83 not currently true of ASN 4294967295, if there is a future need for a
84 Special Use ASN that is not designed to be globally routable, or the
85 associated BGP attributes (such as communities) of such an ASN, this
86 could be a valid candidate for such purpose. This document does not
87 prescribe any such purpose to this ASN.
89 4. Operational Considerations
91 Operators MUST NOT use these Last ASNs as if they are Private Use
92 ASNs, and SHOULD NOT use these Last ASNs for any other purpose,
93 except a Special Uses defined elsewhere. Any other operational use
94 of these Last ASNs could have unpredictable or undesirable results.
95 For example; use of AS 65535 as if it were a Private Use ASN, may
96 result in inadvertent use of BGP Well-known community values
97 [IANA.WK], causing undesired routing behavior.
99 Operators that choose to filter Private Use ASNs within the AS_PATH
100 and AS4_PATH attributes SHOULD also filter these Last ASNs. These
101 last ASNs MUST NOT be advertised to the global Internet within
102 AS_PATH or AS4_PATH attributes.
104 5. Implementation Considerations
106 While these Last ASNs are reserved, they remain valid ASNs from a
107 protocol perspective. Therefore, implementations of BGP [RFC4271]
108 SHOULD NOT treat the use of these Last ASNs as any type of protocol
109 error. However, implementations MAY generate a local warning message
110 indicating probable improper use of a reserved ASN.
112 Implementations that provide tools that filter Private Use ASNs
113 within the AS_PATH and AS4_PATH attributes MAY also include these
114 Last ASNs.
116 6. IANA Considerations
118 IANA has reserved last Autonomous System number 65535 from the
119 "16-bit Autonomous System Numbers" registry for the reasons described
120 in this document.
122 IANA has also reserved last Autonomous System number 4294967295 from
123 the "32-bit Autonomous System Numbers" registry for the reasons
124 described in this document.
126 This reservation has been documented in the IANA Autonomous System
127 Numbers Registry [IANA.AS].
129 7. Security Considerations
131 This document does not introduce any additional security concerns in
132 regards to usage of Last ASNs. Although the BGP protocol is designed
133 to allow usage of these Last ASNs, security issues related to BGP
134 implementation errors could be triggered by Last ASN usage.
136 8. References
138 8.1. Normative References
140 [IANA.AS] IANA, ., "Autonomous System (AS) Numbers", July 2013,
141 .
143 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
144 Requirement Levels", BCP 14, RFC 2119, March 1997.
146 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
147 Protocol 4 (BGP-4)", RFC 4271, January 2006.
149 [RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
150 Autonomous System (AS) Number Space", RFC 6793, December
151 2012.
153 8.2. Informative References
155 [I-D.ietf-idr-as-private-reservation]
156 Mitchell, J., "Autonomous System (AS) Reservation for
157 Private Use", draft-ietf-idr-as-private-reservation-05
158 (work in progress), May 2013.
160 [IANA.WK] IANA, ., "Border Gateway Protocol (BGP) Well-known
161 Communities", July 2013, .
164 [RFC1997] Chandrasekeran, R., Traina, P., and T. Li, "BGP
165 Communities Attribute", RFC 1997, August 1996.
167 Appendix A. Acknowledgements
169 The authors would like to thank Michelle Cotton and Elwyn Davis for
170 encouraging the proper documentation of the reservation of these
171 ASNs. The authors would also like to thank David Farmer for his
172 contributions to the document.
174 Authors' Addresses
176 Jeffrey Haas
177 Juniper Networks
179 Email: jhaas@juniper.net
181 Jon Mitchell
182 Microsoft Corporation
183 One Microsoft Way
184 Redmond, WA 98052
185 USA
187 Email: Jon.Mitchell@microsoft.com