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Checking references for intended status: Informational ---------------------------------------------------------------------------- No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 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