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Mitchell 5 Expires: September 21, 2014 Microsoft Corporation 6 March 20, 2014 8 Reservation of Last Autonomous System (AS) Numbers 9 draft-ietf-idr-last-as-reservation-04 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 September 21, 2014. 35 Copyright Notice 37 Copyright (c) 2014 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 last ASN of the 32 57 bit 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 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 98 While these Last ASNs are reserved, they remain valid ASNs from a BGP 99 protocol perspective. Therefore, implementations of BGP [RFC4271] 100 SHOULD NOT treat the use of these Last ASNs as any type of protocol 101 error. However, implementations MAY generate a local warning message 102 indicating improper use of a reserved ASN. 104 Implementations that provide tools that filter Private Use ASNs 105 within the AS_PATH and AS4_PATH attributes MAY also include these 106 Last ASNs. 108 6. IANA Considerations 110 [Note to IANA, TO BE REMOVED BEFORE PUBLICATION: IANA please update 111 the reservations for values 65535 and 4294967295 in the three 112 registries mentioned below to reference this document. Please note 113 at the time of this comment the "Special-Purpose AS Numbers registry" 114 has not yet been created but should be before publication of this 115 document.] 117 IANA has reserved last Autonomous System number 65535 from the 118 "16-bit Autonomous System Numbers" registry for the reasons described 119 in this document. 121 IANA has reserved last Autonomous System number 65535 from the 122 "16-bit Autonomous System Numbers" registry for the reasons described 123 in this document. 125 IANA has also reserved last Autonomous System number 4294967295 from 126 the "32-bit Autonomous System Numbers" registry for the reasons 127 described in this document. 129 This reservation has been documented in the IANA Autonomous System 130 Numbers Registry [IANA.AS]. 132 This reservation has also been documented in the IANA Special-Purpose 133 AS Numbers Registry as described by [I-D.housley-number-registries]. 135 7. Security Considerations 137 This document does not introduce any additional security concerns in 138 regards to usage of Last ASNs. Although the BGP protocol is designed 139 to allow usage of these Last ASNs, security issues related to BGP 140 implementation errors could be triggered by Last ASN usage. 142 8. References 144 8.1. Normative References 146 [I-D.housley-number-registries] 147 Housley, R., "Internet Numbers Registries", draft-housley- 148 number-registries-04 (work in progress), February 2014. 150 [IANA.AS] IANA, , "Autonomous System (AS) Numbers", March 2014, 151 . 153 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 154 Requirement Levels", BCP 14, RFC 2119, March 1997. 156 [RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway 157 Protocol 4 (BGP-4)", RFC 4271, January 2006. 159 [RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet 160 Autonomous System (AS) Number Space", RFC 6793, December 161 2012. 163 8.2. Informative References 165 [IANA.WK] IANA, , "Border Gateway Protocol (BGP) Well-known 166 Communities", March 2014, . 169 [RFC1997] Chandrasekeran, R., Traina, P., and T. Li, "BGP 170 Communities Attribute", RFC 1997, August 1996. 172 [RFC6996] Mitchell, J., "Autonomous System (AS) Reservation for 173 Private Use", BCP 6, RFC 6996, July 2013. 175 Appendix A. Acknowledgements 177 The authors would like to thank Michelle Cotton and Elwyn Davis for 178 encouraging the proper documentation of the reservation of these ASNs 179 and David Farmer for his contributions to the document. 181 Authors' Addresses 183 Jeffrey Haas 184 Juniper Networks 186 Email: jhaas@juniper.net 187 Jon Mitchell 188 Microsoft Corporation 189 One Microsoft Way 190 Redmond, WA 98052 191 USA 193 Email: Jon.Mitchell@microsoft.com