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(The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document date (January 22, 2019) is 1915 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 180, 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 26, 2019 Internet Initiative Japan 6 R. Bonica 7 Juniper Networks 8 S. Bayraktar 9 Cisco Systems 10 January 22, 2019 12 Well-Known Community Policy Behavior 13 draft-ietf-grow-wkc-behavior-02 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 26, 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 this section we document the syntax and observed behavior of the 134 "set" directive in several popular bgp implementations. 136 In Juniper Networks' JunOS, "community set" removes all received 137 communities, Well-Known or otherwise. 139 In Cisco Systems' IOS-XR, "set community" removes all received 140 communities except for the following: 142 +-------------+-----------------------------------+ 143 | Numeric | Common Name | 144 +-------------+-----------------------------------+ 145 | 0:0 | internet | 146 | 65535:0 | graceful-shutdown | 147 | 65535:1 | accept-own rfc7611 | 148 | 65535:65281 | NO_EXPORT | 149 | 65535:65282 | NO_ADVERTISE | 150 | 65535:65283 | NO_EXPORT_SUBCONFED (or local-AS) | 151 +-------------+-----------------------------------+ 153 Communities not removed by Cisco IOS/XR 155 Table 1 157 IOS-XR does allow Well-Known communities to be removed one at a time 158 by explicit policy; for example, "delete community accept-own". 159 Operators are advised to consult IOS-XR documentation and/or Cisco 160 Systems support for full details. 162 On Brocade NetIron: "set community X" removes all communities and 163 sets X. 165 In Huawei's VRP product, "community set" removes all received 166 communities, well-Known or otherwise. 168 In OpenBSD's OpenBGPD, "set community" does not remove any 169 communities, Well-Known or otherwise. 171 4.1. Note on an Inconsistency 173 The IANA publishes a list of Well-Known Communities [IANA-WKS]. 175 IOS-XR's set of well-known communities that "set community" will not 176 overwrite diverges from IANA's list. Quite a few well-known 177 communities from IANA's list do not receive special treatment in IOS- 178 XR, and at least one specific community on IOS-XR's special treatment 179 list (internet == 0:0) is not really on IANA's list -- it's taken 180 from the "Reserved" range [0x00000000-0x0000FFFF]. 182 This merely notes an inconsistency. It is not a plea to 'protect' 183 the entire IANA list from "set community." 185 5. Note for Those Writing RFCs for New Community-Like Attributes 187 Care should be taken when establishing new [RFC1997]-like attributes 188 (large communities, wide communities, etc) to avoid repeating this 189 mistake. 191 6. Action Items 193 Unfortunately, it would be operationally disruptive for vendors to 194 change their current implementations. 196 Vendors SHOULD clearly document the behavior of "set" directive in 197 their implementations. 199 Vendors MUST ensure that any Well-Known Communities specified after 200 this document's publication are removed by their "set" directive. 202 Given the implementation inconsistencies described in this document, 203 network operators are urged never to rely on any implicit 204 understanding of a neighbor ASN's bgp community handling. I.e., 205 before announcing prefixes with NO_EXPORT or any other community to a 206 neighbor ASN, the operator should confirm with that neighbor how the 207 community will be treated. 209 Network operators are encouraged to limit their use of the "set" 210 directive (within reason), to improve the readability of their 211 configurations and hopefully to achieve behavioral consistency across 212 platforms. 214 7. Security Considerations 216 Surprising defaults and/or undocumented behaviors are not good for 217 security. This document attempts to remedy that. 219 8. IANA Considerations 221 This document has no IANA Considerations other than to be aware that 222 any future Well-Known Communities will be subject to the policy 223 treatment described here. 225 9. Acknowledgements 227 The authors thank Martijn Schmidt, Qin Wu for the Huawei data point, 228 Job Snijders, David Farmer,John Heasley, and Jakob Heitz. 230 10. Normative References 232 [IANA-WKS] 233 "IANA Well-Known Comunities", 234 . 237 [RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities 238 Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996, 239 . 241 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 242 Requirement Levels", BCP 14, RFC 2119, 243 DOI 10.17487/RFC2119, March 1997, 244 . 246 Authors' Addresses 248 Jay Borkenhagen 249 AT&T 250 200 Laurel Avenue South 251 Middletown, NJ 07748 252 United States of America 254 Email: jayb@att.com 256 Randy Bush 257 Internet Initiative Japan 258 5147 Crystal Springs 259 Bainbridge Island, WA 98110 260 United States of America 262 Email: randy@psg.com 264 Ron Bonica 265 Juniper Networks 266 2251 Corporate Park Drive 267 Herndon, VA 20171 268 US 270 Email: rbonica@juniper.net 272 Serpil Bayraktar 273 Cisco Systems 274 170 W. Tasman Drive 275 San Jose, CA 95134 276 United States of America 278 Email: serpil@cisco.com