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(The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document date (January 7, 2019) is 1935 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: '0x00000000-0x0000FFFF' is mentioned on line 177, but not defined -- Possible downref: Non-RFC (?) normative reference: ref. 'IANA-WKS' Summary: 0 errors (**), 0 flaws (~~), 3 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group J. Borkenhagen 3 Internet-Draft AT&T 4 Intended status: Standards Track R. Bush 5 Expires: July 11, 2019 Internet Initiative Japan 6 R. Bonica 7 Juniper Networks 8 S. Bayraktar 9 Cisco Systems 10 January 7, 2019 12 Well-Known Community Policy Behavior 13 draft-ietf-grow-wkc-behavior-01 15 Abstract 17 Well-Known BGP Communities are manipulated inconsistently by current 18 implementations. This results in difficulties for operators. 19 Network operators are encouraged to deploy consistent community 20 handling across their networks, taking the inconsistent behaviors 21 from the various bgp implementations they operate into consideration. 22 Also, bgp implementors are expected to not create any further 23 inconsistencies from this point forward. 25 Requirements Language 27 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 28 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to 29 be interpreted as described in RFC 2119 [RFC2119] only when they 30 appear in all upper case. They may also appear in lower or mixed 31 case as English words, without normative meaning. 33 Status of This Memo 35 This Internet-Draft is submitted in full conformance with the 36 provisions of BCP 78 and BCP 79. 38 Internet-Drafts are working documents of the Internet Engineering 39 Task Force (IETF). Note that other groups may also distribute 40 working documents as Internet-Drafts. The list of current Internet- 41 Drafts is at https://datatracker.ietf.org/drafts/current/. 43 Internet-Drafts are draft documents valid for a maximum of six months 44 and may be updated, replaced, or obsoleted by other documents at any 45 time. It is inappropriate to use Internet-Drafts as reference 46 material or to cite them other than as "work in progress." 48 This Internet-Draft will expire on July 11, 2019. 50 Copyright Notice 52 Copyright (c) 2019 IETF Trust and the persons identified as the 53 document authors. All rights reserved. 55 This document is subject to BCP 78 and the IETF Trust's Legal 56 Provisions Relating to IETF Documents 57 (https://trustee.ietf.org/license-info) in effect on the date of 58 publication of this document. Please review these documents 59 carefully, as they describe your rights and restrictions with respect 60 to this document. Code Components extracted from this document must 61 include Simplified BSD License text as described in Section 4.e of 62 the Trust Legal Provisions and are provided without warranty as 63 described in the Simplified BSD License. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 68 2. Manipulation of Communities by Policy . . . . . . . . . . . . 3 69 3. Community Manipulation Policy Differences . . . . . . . . . . 3 70 4. Documentation of Vendor Implementations . . . . . . . . . . . 3 71 4.1. Note on an Inconsistency . . . . . . . . . . . . . . . . 4 72 5. Note for Those Writing RFCs for New Community-Like 73 Attributes . . . . . . . . . . . . . . . . . . . . . . . . . 4 74 6. Action Items . . . . . . . . . . . . . . . . . . . . . . . . 5 75 7. Security Considerations . . . . . . . . . . . . . . . . . . . 5 76 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 77 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 78 10. Normative References . . . . . . . . . . . . . . . . . . . . 5 79 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6 81 1. Introduction 83 The BGP Communities Attribute was specified in [RFC1997] which 84 introduced the concept of Well-Known Communities. In hindsight, 85 [RFC1997] did not prescribe as fully as it should have how Well-Known 86 Communities may be manipulated by policies applied by operators. 87 Currently, implementations differ in this regard, and these 88 differences can result in inconsistent behaviors that operators find 89 difficult to identify and resolve. 91 This document describes the current behavioral differences in order 92 to assist operators in generating consistent community-manipulation 93 policies in a multi-vendor environment, and to prevent the 94 introduction of additional divergence in implementations. 96 2. Manipulation of Communities by Policy 98 [RFC1997] says: 100 "A BGP speaker receiving a route with the COMMUNITIES path attribute 101 may modify this attribute according to the local policy." 103 A basic operational need is to add or remove one or more communities 104 to the received set. Another common need is to replace all received 105 communities with a new set. To simplify the second case, most BGP 106 policy implementations provide syntax to "set" community that 107 operators use to mean "remove any/all communities present on the 108 update received from the neighbor, and apply this set of communities 109 instead." 111 Some operators prefer to write explicit policy to delete unwanted 112 communities rather than using "set;" i.e. using a "delete community 113 *:*" and then "add community x:y ..." configuration statements in an 114 attempt to replace all received communities. The same community 115 manipulation policy differences described in the following section 116 exist in both "set" and "delete community *:*" syntax. For 117 simplicity, the remainder of this document refers only to the "set" 118 behaviors. 120 3. Community Manipulation Policy Differences 122 Vendor implementations differ in the treatment of certain Well-Known 123 communities when modified using the syntax to "set" the community. 124 Some replace all communities including the Well-Known ones with the 125 new set, while others replace all non-Well-Known Communities but do 126 not modify any Well-Known Communities that are present. 128 These differences result in what would appear to be identical policy 129 configurations having very different results on different platforms. 131 4. Documentation of Vendor Implementations 133 In Juniper Networks' JunOS, "community set" removes all received 134 communities, Well-Known or otherwise. 136 In Cisco Systems' IOS-XR, "set community" removes all received 137 communities except for the following: 139 +-------------+-----------------------------------+ 140 | Numeric | Common Name | 141 +-------------+-----------------------------------+ 142 | 0:0 | internet | 143 | 65535:0 | graceful-shutdown | 144 | 65535:1 | accept-own rfc7611 | 145 | 65535:65281 | NO_EXPORT | 146 | 65535:65282 | NO_ADVERTISE | 147 | 65535:65283 | NO_EXPORT_SUBCONFED (or local-AS) | 148 +-------------+-----------------------------------+ 150 Communities not removed by Cisco IOS/XR 152 Table 1 154 IOS-XR does allow Well-Known communities to be removed one at a time 155 by explicit policy; for example, "delete community accept-own". 156 Operators are advised to consult IOS-XR documentation and/or Cisco 157 Systems support for full details. 159 On Brocade NetIron: "set community X" removes all communities and 160 sets X. 162 In Huawei's VRP product, "community set" removes all received 163 communities, well-Known or otherwise. 165 In OpenBSD's OpenBGPD, "set community" does not remove any 166 communities, Well-Known or otherwise. 168 4.1. Note on an Inconsistency 170 The IANA publishes a list of Well-Known Communities [IANA-WKS]. 172 IOS-XR's set of well-known communities that "set community" will not 173 overwrite diverges from IANA's list. Quite a few well-known 174 communities from IANA's list do not receive special treatment in IOS- 175 XR, and at least one specific community on IOS-XR's special treatment 176 list (internet == 0:0) is not really on IANA's list -- it's taken 177 from the "Reserved" range [0x00000000-0x0000FFFF]. 179 This merely notes an inconsistency. It is not a plea to 'protect' 180 the entire IANA list from "set community." 182 5. Note for Those Writing RFCs for New Community-Like Attributes 184 Care should be taken when establishing new [RFC1997]-like attributes 185 (large communities, wide communities, etc) to avoid repeating this 186 mistake. 188 6. Action Items 190 Unfortunately, it would be operationally disruptive for vendors to 191 change their current implementations. 193 Vendors SHOULD share the behavior of their implementations for 194 inclusion in this document, especially if their behavior differs from 195 the examples described. 197 Vendors MUST ensure that any well-known communities specified after 198 this document's publication are removed by the "community set" 199 action. 201 Given the implementation inconsistencies described in this document, 202 network operators are urged never to rely on any implicit 203 understanding of a neighbor ASN's bgp community handling. I.e., 204 before announcing prefixes with NO_EXPORT or any other community to a 205 neighbor ASN, the operator should confirm with that neighbor how the 206 community will be treated. 208 7. Security Considerations 210 Surprising defaults and/or undocumented behaviors are not good for 211 security. This document attempts to remedy that. 213 8. IANA Considerations 215 This document has no IANA Considerations other than to be aware that 216 any future Well-Known Communities will be subject to the policy 217 treatment described here. 219 9. Acknowledgements 221 The authors thank Martijn Schmidt for his contribution, Qin Wu for 222 the Huawei data point. 224 10. Normative References 226 [IANA-WKS] 227 "IANA Well-Known Comunities", 228 . 231 [RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities 232 Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996, 233 . 235 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 236 Requirement Levels", BCP 14, RFC 2119, 237 DOI 10.17487/RFC2119, March 1997, 238 . 240 Authors' Addresses 242 Jay Borkenhagen 243 AT&T 244 200 Laurel Avenue South 245 Middletown, NJ 07748 246 United States of America 248 Email: jayb@att.com 250 Randy Bush 251 Internet Initiative Japan 252 5147 Crystal Springs 253 Bainbridge Island, WA 98110 254 United States of America 256 Email: randy@psg.com 258 Ron Bonica 259 Juniper Networks 260 2251 Corporate Park Drive 261 Herndon, VA 20171 262 US 264 Email: rbonica@juniper.net 266 Serpil Bayraktar 267 Cisco Systems 268 170 W. Tasman Drive 269 San Jose, CA 95134 270 United States of America 272 Email: serpil@cisco.com