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2 Network Working Group J. Haas
3 Internet-Draft Juniper Networks
4 Intended status: Informational J. Mitchell
5 Expires: November 17, 2013 Microsoft Corporation
6 May 16, 2013
8 Last Autonomous System (AS) Reservations
9 draft-jhjm-idr-last-as-reservations-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 recommends they not be used by operators.
17 Status of This Memo
19 This Internet-Draft is submitted in full conformance with the
20 provisions of BCP 78 and BCP 79.
22 Internet-Drafts are working documents of the Internet Engineering
23 Task Force (IETF). Note that other groups may also distribute
24 working documents as Internet-Drafts. The list of current Internet-
25 Drafts is at http://datatracker.ietf.org/drafts/current/.
27 Internet-Drafts are draft documents valid for a maximum of six months
28 and may be updated, replaced, or obsoleted by other documents at any
29 time. It is inappropriate to use Internet-Drafts as reference
30 material or to cite them other than as "work in progress."
32 This Internet-Draft will expire on November 17, 2013.
34 Copyright Notice
36 Copyright (c) 2013 IETF Trust and the persons identified as the
37 document authors. All rights reserved.
39 This document is subject to BCP 78 and the IETF Trust's Legal
40 Provisions Relating to IETF Documents
41 (http://trustee.ietf.org/license-info) in effect on the date of
42 publication of this document. Please review these documents
43 carefully, as they describe your rights and restrictions with respect
44 to this document. Code Components extracted from this document must
45 include Simplified BSD License text as described in Section 4.e of
46 the Trust Legal Provisions and are provided without warranty as
47 described in the Simplified BSD License.
49 1. Introduction
51 IANA has reserved the last Autonomous System Number (ASN), 65535, of
52 the 16 bit autonomous system number range for over a decade with the
53 intention that it not be used by BGP [RFC4271] network operators.
54 Since the introduction of BGP Support for Four-Octet AS Number Space
55 [RFC6793], IANA has also reserved the ASN of the 32 bit autonomous
56 system number range, 4294967295. These reservations have been
57 documented in the IANA Autonomous System Numbers Registry [IANA.AS].
58 Although these "Last ASNs" border on Private Use ASN ranges, they are
59 not defined as Private Use ASNs by
60 [I-D.ietf-idr-as-private-reservation]. This document describes the
61 reasoning for these reservations and provides guidance both to
62 operators and to authors of future protocol enhancements on their
63 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 ASN Reservations
73 The primary reason for reserving the Last ASNs of the 16 bit and 32
74 bit ASN ranges is that these numbers are also at the end of typical
75 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 RFC 1997 [RFC1997] and IANA [IANA.WK].
83 Although this not currently true of ASN 4294967295, if there is a
84 future need for a Special Use ASN that is not designed to be globally
85 routable, or the associated BGP attributes (such as communities) of
86 such an ASN, this may be a valid candidate for such purpose. This
87 document does not prescribe any such purpose to this ASN.
89 4. Operational Considerations
91 Operators MUST NOT use Last ASNs as if they are Private Use ASNs, or
92 for any other purpose, since they are reserved and implementations
93 may have errors in regards to handling these ASNs. Implementations
94 SHOULD NOT handle Last ASNs in the same fashion as Private Use ASNs.
95 Operators are accustomed to being able to fully utilize the
96 communities associated with the ASN's they have deployed utilizing
97 the format described in RFC 1997 [RFC1997], even in the case of
98 Private Use ASNs. In the case of usage of ASN 65535 as if it was a
99 Private Use ASN, operators might not recognize these communities are
100 reserved as BGP Well-known community values [IANA.WK], causing
101 undesirable routing behavior if prefixes are tagged with such
102 communities within the network.
104 Operators that choose to filter or provide tools that filter AS_PATH,
105 MAY choose to filter Last ASNs in the same way as Private Use ASNs,
106 to prevent the use of these reserved ASNs on their networks.
108 5. Acknowledgements
110 The author would like to thank Michelle Cotton and Elwyn Davis for
111 encouraging the proper documentation of the reservation of these
112 ASNs.
114 6. IANA Considerations
116 IANA has reserved Autonomous System number 65535 from the "16-bit
117 Autonomous System Numbers" registry for the reasons described in this
118 document.
120 IANA has also reserved Autonomous System number 4294967295 from the
121 "32-bit Autonomous System Numbers" registry for the reasons described
122 in this document.
124 These reservations have been documented in the IANA Autonomous System
125 Numbers Registry [IANA.AS].
127 7. Security Considerations
129 This document does not introduce any additional security concerns in
130 regards to the Last ASNs usage. Although the BGP protocol is
131 designed to allow usage of these Last ASNs, security issues related
132 to BGP implementation errors may be triggered by Last ASN usage.
134 8. References
136 8.1. Normative References
138 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
139 Requirement Levels", BCP 14, RFC 2119, March 1997.
141 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
142 Protocol 4 (BGP-4)", RFC 4271, January 2006.
144 [RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
145 Autonomous System (AS) Number Space", RFC 6793, December
146 2012.
148 8.2. Informative References
150 [I-D.ietf-idr-as-private-reservation]
151 Mitchell, J., "Autonomous System (AS) Reservation for
152 Private Use", draft-ietf-idr-as-private-reservation-04
153 (work in progress), April 2013.
155 [IANA.AS] IANA, "Autonomous System (AS) Numbers", May 2013,
156 .
158 [IANA.WK] IANA, "Border Gateway Protocol (BGP) Well-known
159 Communities", May 2013, .
162 [RFC1997] Chandrasekeran, R., Traina, P., and T. Li, "BGP
163 Communities Attribute", RFC 1997, August 1996.
165 Authors' Addresses
167 Jeffrey Haas
168 Juniper Networks
170 Email: jhaas@juniper.net
172 Jon Mitchell
173 Microsoft Corporation
174 One Microsoft Way
175 Redmond, WA 98052
176 USA
178 Email: Jon.Mitchell@microsoft.com