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Mitchell 5 Expires: April 18, 2014 Microsoft Corporation 6 October 15, 2013 8 Reservation of Last Autonomous System (AS) Numbers 9 draft-ietf-idr-last-as-reservation-01 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 April 18, 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 [RFC6996] ranges, they are not defined or reserved as Private Use 61 ASNs by [IANA.AS]. This document describes the reasoning for 62 reserving these Last ASNs and provides guidance both to operators and 63 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 A subset of the BGP communities of ASN 65535, the last ASN of the 16 74 bit range, are reserved for use by Well-known communities as 75 described in [RFC1997] and [IANA.WK]. Although this is not currently 76 true of ASN 4294967295, if there is a future need for another Special 77 Use ASN that is not designed to be globally routable, or the 78 associated BGP communities of such an ASN, ASN 4294967295 could be a 79 valid candidate for such purpose. This document does not prescribe 80 any such Special Use to this ASN at the time of publication. 82 4. Operational Considerations 84 Operators SHOULD NOT use these Last ASNs as if they are Private Use 85 ASNs or for any other purpose. Operational use of these Last ASNs 86 could have undesirable results. For example; use of AS 65535 as if 87 it were a Private Use ASN, may result in inadvertent use of BGP Well- 88 known Community values [IANA.WK], causing undesireable routing 89 behavior. 91 These last ASNs MUST NOT be advertised to the global Internet within 92 AS_PATH or AS4_PATH attributes. Operators that choose to do inbound 93 filtering of Private Use ASNs within the AS_PATH and AS4_PATH 94 attributes SHOULD also filter these Last ASNs. 96 5. Implementation Considerations 97 While these Last ASNs are reserved, they remain valid ASNs from a BGP 98 protocol perspective. Therefore, implementations of BGP [RFC4271] 99 SHOULD NOT treat the use of these Last ASNs as any type of protocol 100 error. However, implementations MAY generate a local warning message 101 indicating improper use of a reserved ASN. 103 Implementations that provide tools that filter Private Use ASNs 104 within the AS_PATH and AS4_PATH attributes MAY also include these 105 Last ASNs. 107 6. IANA Considerations 109 IANA has reserved last Autonomous System number 65535 from the 110 "16-bit Autonomous System Numbers" registry for the reasons described 111 in this document. 113 IANA has also reserved last Autonomous System number 4294967295 from 114 the "32-bit Autonomous System Numbers" registry for the reasons 115 described in this document. 117 This reservation has been documented in the IANA Autonomous System 118 Numbers Registry [IANA.AS]. 120 7. Security Considerations 122 This document does not introduce any additional security concerns in 123 regards to usage of Last ASNs. Although the BGP protocol is designed 124 to allow usage of these Last ASNs, security issues related to BGP 125 implementation errors could be triggered by Last ASN usage. 127 8. References 129 8.1. Normative References 131 [IANA.AS] IANA, ., "Autonomous System (AS) Numbers", October 2013, 132 . 134 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 135 Requirement Levels", BCP 14, RFC 2119, March 1997. 137 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway 138 Protocol 4 (BGP-4)", RFC 4271, January 2006. 140 [RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet 141 Autonomous System (AS) Number Space", RFC 6793, December 142 2012. 144 8.2. Informative References 146 [IANA.WK] IANA, ., "Border Gateway Protocol (BGP) Well-known 147 Communities", October 2013, . 150 [RFC1997] Chandrasekeran, R., Traina, P., and T. Li, "BGP 151 Communities Attribute", RFC 1997, August 1996. 153 [RFC6996] Mitchell, J., "Autonomous System (AS) Reservation for 154 Private Use", BCP 6, RFC 6996, July 2013. 156 Appendix A. Acknowledgements 158 The authors would like to thank Michelle Cotton and Elwyn Davis for 159 encouraging the proper documentation of the reservation of these ASNs 160 and David Farmer for his contributions to the document. 162 Authors' Addresses 164 Jeffrey Haas 165 Juniper Networks 167 Email: jhaas@juniper.net 169 Jon Mitchell 170 Microsoft Corporation 171 One Microsoft Way 172 Redmond, WA 98052 173 USA 175 Email: Jon.Mitchell@microsoft.com