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Heasly 9 September 9, 2020 11 BGP Well Known Large Community 12 draft-heitz-idr-wklc-01 14 Abstract 16 A range of BGP Autonomous System Numbers is reserved to create a set 17 of BGP Well Known Large Communities. 19 Requirements Language 21 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 22 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 23 document are to be interpreted as described in [RFC2119]. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at https://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on March 13, 2021. 42 Copyright Notice 44 Copyright (c) 2020 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (https://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 2. Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . 2 61 3. Transitivity . . . . . . . . . . . . . . . . . . . . . . . . 3 62 4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 4 63 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 64 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 65 7. Normative References . . . . . . . . . . . . . . . . . . . . 5 66 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 68 1. Introduction 70 The Global Administrator field of the BGP Large community [RFC8092] 71 is an Autonomous System Number (ASN). To create a set of Well Known 72 Large Communities, a set of ASNs must be reserved for them, such that 73 a real ASN in the Global Administrator field cannot be mistaken for a 74 Well Known Large Community. 76 2. Encoding 78 Each BGP Well Known Large Community value is encoded as a 12-octet 79 quantity, as follows: 81 0 1 2 3 82 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 83 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 84 |1 1 1 1 0 1| T | WKLC ID | Data 1 | 85 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 86 | Data 2 | 87 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 88 | Data 3 | 89 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 91 The fields are as shown below: 93 T - Transitivity field (2 bits). This is further 94 described below. 96 WKLC ID - Well Known Large Community Identifier (1 octet). 97 See IANA Considerations. If an experimental type 98 is used, then it MUST NOT be hard coded in the BGP 99 speaker software; it MUST be configurable. 100 Different experiments can then run in the same 101 network without having to coordinate identifier 102 assignment during the coding stage. 104 Data 1,2,3 - A 10 octet value specific to the WKLC. Data 1 is 105 16 bits long and Data 2 and Data 3 are 32 bits long 106 each. The data portion is divided into the three 107 fields only to encourage a canonical representation 108 that follows [RFC8092]. If any WKLC cannot make 109 use of this data division, it is free to define 110 another division. 112 3. Transitivity 114 The Large Community path attribute is a transitive attribute. Thus, 115 BGP speakers that do not implement the transitivity described here 116 will transit the WKLC regardless. If such a speaker wishes not to 117 receive a particular large community, it MUST filter it out using 118 local policy. The transitivity field determines how BGP speakers 119 transfer the WKLC across real Autonomous System (AS) boundaries. The 120 values are: 122 0 - Transitive: The WKLC is transitive across ASes. 124 1 - Non-transitive: The WKLC is not transitive across ASes. 126 2 - Administration Transitive: The WKLC is transitive across 127 ASes under the same administration only. By default, every 128 AS boundary is also an administration boundary. If an 129 external BGP session is configured as a non-administrative 130 boundary, then it will send and receive WKLCs with 131 transitivity 2, else it will discard the WKLC from the 132 UPDATE message. 134 3 - One-time Transitive: The WKLC is transitive across ASes 135 under the same administration and into an AS under the 136 neighboring administration, but not into an AS under a 137 further administration. A BGP speaker that receives a WKLC 138 with transitivity 3 on an external BGP session on an 139 administrative boundary SHOULD change the transitivity to 2. 141 4. Discussion 143 A criterion considered important is the number of data octets 144 available for any WKLC type. This is maximized to 10 at the expense 145 of ASN space and type space. 147 8 bits for the type is considered to be plenty. 255 types are more 148 than enough for WKLC, considering how many extended community types 149 have been used so far (19 at time of this publication). If a large 150 set of types, each of which requires less than 10 octets of data, is 151 required, then they can all be specified under a single type code and 152 further distinguished by using the Data 1 field as a sub-type. An 153 equivalent example is the EVPN Extended Community type, which defines 154 further sub types. 156 The range of AS numbers currently unallocated by IANA is 399,261 to 157 4,199,999,999. The WKLC reserves 67,108,864 AS numbers. That still 158 leaves 4,132,491,874 unallocated AS numbers. For comparison, there 159 are 94,968,317 AS numbers reserved for private use. Thus, the number 160 of ASNs reserved for WKLCs is considered insignificant. 162 5. Security Considerations 164 The BGP Large Community Path attribute is transitive. Thus, a BGP 165 speaker that does not recognize the transitivity field may transmit 166 the WKLC contrary to the advisement of the transitivity field. If a 167 BGP speaker wishes not to receive any Large Community, it must 168 continue to filter it in the same way it was doing before the 169 transitivity field was introduced. 171 In some cases, a received route that contains an AS number from the 172 range assigned to WKLC in its AS_PATH may be considered unusual. A 173 receiving BGP speaker MAY drop such a received route in route-policy. 175 6. IANA Considerations 177 IANA is requested to assign the range 4093640704 (0xF4000000) to 178 4160749567 (0xF7FFFFFF) from the BGP ASN registry for BGP Well Known 179 Large Communities. 181 IANA is requested to create a registry of Well Known Large 182 Communities in the range 0 to 255. Numbers from this registry are to 183 be assigned in accordance with the policies defined in [RFC8126]. 184 The policies for the following number ranges are: 186 0-63 - RFC Required 188 64-223 - First Come First Served 189 224-255 - Experimental 191 7. Normative References 193 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 194 Requirement Levels", BCP 14, RFC 2119, 195 DOI 10.17487/RFC2119, March 1997, 196 . 198 [RFC8092] Heitz, J., Ed., Snijders, J., Ed., Patel, K., Bagdonas, 199 I., and N. Hilliard, "BGP Large Communities Attribute", 200 RFC 8092, DOI 10.17487/RFC8092, February 2017, 201 . 203 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 204 Writing an IANA Considerations Section in RFCs", BCP 26, 205 RFC 8126, DOI 10.17487/RFC8126, June 2017, 206 . 208 Authors' Addresses 210 Jakob Heitz 211 Cisco 212 170 West Tasman Drive 213 San Jose, CA 95134 214 USA 216 Email: jheitz@cisco.com 218 Kotikalapudi Sriram 219 USA National Institute of Standards and Technology 220 100 Bureau Drive 221 Gaithersburg, MD 20899 222 USA 224 Email: kotikalapudi.sriram@nist.gov 226 Brian Dickson 228 Email: brian.peter.dickson@gmail.com 230 John Heasly 232 Email: heas@shrubbery.net