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Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (December 27, 2018) is 1945 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) No issues found here. Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Global Routing Operations J. Snijders 3 Internet-Draft NTT Communications 4 Intended status: Standards Track M. Aelmans 5 Expires: June 30, 2019 Juniper Networks 6 December 27, 2018 8 BGP Maximum Prefix Limits 9 draft-sa-grow-maxprefix-01 11 Abstract 13 This document describes mechanisms to limit the negative impact of 14 route leaks [RFC7908] and/or resource exhaustion in BGP-4 [RFC4271] 15 implementations. 17 Requirements Language 19 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 20 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 21 "OPTIONAL" in this document are to be interpreted as described in BCP 22 14 [RFC2119] [RFC8174] when, and only when, they appear in all 23 capitals, as shown here. 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 June 30, 2019. 42 Copyright Notice 44 Copyright (c) 2018 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. Application of Control Theory to BGP-4 Operations . . . . . . 2 61 3. Inbound Maximum Prefix Limits . . . . . . . . . . . . . . . . 2 62 3.1. Type A: Pre-Policy Inbound Maximum Prefix Limits . . . . 3 63 3.2. Type B: Post-Policy Inbound Maximum Prefix Limits . . . . 3 64 4. Outbound Maximum Prefix Limits . . . . . . . . . . . . . . . 3 65 5. Considerations for Operations with Multi-Protocol BGP-4 . . . 4 66 6. Considerations for soft thresholds . . . . . . . . . . . . . 4 67 7. Security Considerations . . . . . . . . . . . . . . . . . . . 4 68 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 69 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5 70 10. Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION 5 71 11. Appendix: Implementation Guidance . . . . . . . . . . . . . . 6 72 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 73 12.1. Normative References . . . . . . . . . . . . . . . . . . 6 74 12.2. Informative References . . . . . . . . . . . . . . . . . 7 75 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 77 1. Introduction 79 This document describes mechanisms to reduce the negative impact of 80 certain types of misconfigurations and/or resource exhaustions in 81 BGP-4 [RFC4271] operations. While [RFC4271] already described a 82 method to tear down BGP-4 sessions when certain thresholds are 83 exceeded, some nuances in this specification were missing resulting 84 in inconsistencies between BGP-4 implementations. In addition to 85 clarifying "inbound maximum prefix limits", this document also 86 introduces a specification for "outbound maximum prefix limits". 88 2. Application of Control Theory to BGP-4 Operations 90 3. Inbound Maximum Prefix Limits 92 An operator MAY configure a BGP speaker to terminate its BGP session 93 with a neighbor when the number of address prefixes received from 94 that neighbor exceeds a locally configured upper limit. The BGP 95 speaker then MUST send the neighbor a NOTIFICATION message with the 96 Error Code Cease and the Error Subcode "Threshold reached: Maximum 97 Number of Prefixes Received", and MAY support other actions. 98 Reporting when thresholds have been exceeded is an implementation 99 specific consideration, but SHOULD include methods such as Syslog 100 [RFC5424]. Inbound Maximum Prefix Limits can be applied in two 101 distinct places in the conceptual model: before or after the 102 application of routing policy. 104 3.1. Type A: Pre-Policy Inbound Maximum Prefix Limits 106 The Adj-RIBs-In stores routing information learned from inbound 107 UPDATE messages that were received from another BGP speaker 108 Section 3.2 [RFC4271]. The Type A pre-policy limit uses the number 109 of NLRIs per Address Family Identifier (AFI) per Subsequent Address 110 Family Identifier (SAFI) as input into its threshold comparisons. 111 For example, when an operator configures the Type A pre-policy limit 112 for IPv4 Unicast to be 50 on a given EBGP session, and the other BGP 113 speaker announces its 51st IPv4 Unicast NLRI, the session MUST be 114 terminated. 116 Type A pre-policy limits are particularly useful to help dampen the 117 effects of full table route leaks and memory exhaustion when the 118 implementation stores rejected routes. 120 3.2. Type B: Post-Policy Inbound Maximum Prefix Limits 122 RFC4271 describes a Policy Information Base (PIB) that contains local 123 policies that can be applied to the information in the Routing 124 Information Base (RIB). The Type B post-policy limit uses the number 125 of NLRIs per Address Family Identifier (AFI) per Subsequent Address 126 Family Identifier (SAFI), after application of the Import Policy as 127 input into its threshold comparisons. For example, when an operator 128 configures the Type B post-policy limit for IPv4 Unicast to be 50 on 129 a given EBGP session, and the other BGP speaker announces a hundred 130 IPv4 Unicast routes of which none are accepted as a result of the 131 local import policy (and thus not considered for the Loc-RIB by the 132 local BGP speaker), the session is not terminated. 134 Type B post-policy limits are useful to help prevent FIB exhaustion. 136 4. Outbound Maximum Prefix Limits 138 An operator MAY configure a BGP speaker to terminate its BGP session 139 with a neighbor when the number of address prefixes to be advertised 140 to that neighbor exceeds a locally configured upper limit. The BGP 141 speaker then MUST send the neighbor a NOTIFICATION message with the 142 Error Code Cease and the Error Subcode "Threshold reached: Maximum 143 Number of Prefixes Send", and MAY support other actions. Reporting 144 when thresholds have been exceeded is an implementation specific 145 consideration, but SHOULD include methods such as Syslog [RFC5424]. 146 By definition, Outbound Maximum Prefix Limits are Post-Policy. 148 The Adj-RIBs-Out stores information selected by the local BGP speaker 149 for advertisement to its neighbors. The routing information stored 150 in the Adj-RIBs-Out will be carried in the local BGP speaker's UPDATE 151 messages and advertised to its neighbors Section 3.2 [RFC4271]. The 152 Outbound Maximum Prefix Limit uses the number of NLRIs per Address 153 Family Identifier (AFI) per Subsequent Address Family Identifier 154 (SAFI), after application of the Export Policy, as input into its 155 threshold comparisons. For example, when an operator configures the 156 Outbound Maximum Prefix Limit for IPv4 Unicast to be 50 on a given 157 EBGP session, and were about to announce its 51st IPv4 Unicast NLRI 158 to the other BGP speaker as a result of the local export policy, the 159 session MUST be terminated. 161 Outbound Maximum Prefix Limits are useful to help dampen the negative 162 effects of a misconfiguration in local policy. In many cases, it 163 would be more desirable to tear down a BGP session rather than 164 causing or propagating a route leak. 166 5. Considerations for Operations with Multi-Protocol BGP-4 168 6. Considerations for soft thresholds 170 describe soft and hard limits (warning vs teardown) 172 7. Security Considerations 174 TBD. Maximum Prefix Limits are an essential tool for routing 175 operations. 177 8. IANA Considerations 179 This memo requests that IANA updates the name of subcode "Maximum 180 Number of Prefixes Reached" to "Threshold exceeded: Maximum Number of 181 Prefixes Received" in the "Cease NOTIFICATION message subcodes" 182 registry under the "Border Gateway Protocol (BGP) Parameters" group. 184 This memo requests that IANA assigns a new subcode named "Threshold 185 exceeded: Maximum Number of Prefixes Send" in the "Cease NOTIFICATION 186 message subcodes" registry under the "Border Gateway Protocol (BGP) 187 Parameters" group. 189 9. Acknowledgments 191 The authors would like to thank Saku Ytti and John Heasley (NTT 192 Communications), Jeff Haas, Colby Barth and John Scudder (Juniper 193 Networks), Martijn Schmidt (i3D.net), Teun Vink (BIT), Sabri Berisha 194 (eBay), Martin Pels (Quanza), Steven Bakker (AMS-IX) and Aftab 195 Siddiqui (ISOC) for their support, insightful review, and comments. 197 10. Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION 199 This section records the status of known implementations of the 200 protocol defined by this specification at the time of posting of this 201 Internet-Draft, and is based on a proposal described in RFC7942. The 202 description of implementations in this section is intended to assist 203 the IETF in its decision processes in progressing drafts to RFCs. 204 Please note that the listing of any individual implementation here 205 does not imply endorsement by the IETF. Furthermore, no effort has 206 been spent to verify the information presented here that was supplied 207 by IETF contributors. This is not intended as, and must not be 208 construed to be, a catalog of available implementations or their 209 features. Readers are advised to note that other implementations may 210 exist. 212 The below table provides an overview (as of the moment of writing) of 213 which vendors have produced implementation of inbound or outbound 214 maximum prefix limits. Each table cell shows the applicable 215 configuration keywords if the vendor implemented the feature. 217 +-------------+----------------+-------------------------+----------+ 218 | Vendor | Type A Pre- | Type B Post-Policy | Outbound | 219 | | Policy | | | 220 +-------------+----------------+-------------------------+----------+ 221 | Cisco IOS | | maximum-prefix | | 222 | XR | | | | 223 +-------------+----------------+-------------------------+----------+ 224 | Cisco IOS | | maximum-prefix | | 225 | XE | | | | 226 +-------------+----------------+-------------------------+----------+ 227 | Juniper | prefix-limit | accepted-prefix-limit, | | 228 | Junos OS | | or prefix-limit | | 229 | | | combined with 'keep | | 230 | | | none' | | 231 +-------------+----------------+-------------------------+----------+ 232 | Nokia SR OS | prefix-limit | | | 233 +-------------+----------------+-------------------------+----------+ 234 | NIC.CZ BIRD | 'import keep | 'import limit' or | export | 235 | | filtered' | 'receive limit' | limit | 236 | | combined with | | | 237 | | 'receive | | | 238 | | limit' | | | 239 +-------------+----------------+-------------------------+----------+ 240 | OpenBSD | max-prefix | | | 241 | OpenBGPD | | | | 242 +-------------+----------------+-------------------------+----------+ 243 | Arista EOS | maximum-routes | maximum-accepted-routes | 244 +-------------+----------------+-------------------------+----------+ 246 First presented by Snijders at [RIPE77] 248 Table 1: Maximum prefix limits capabilities per implementation 250 11. Appendix: Implementation Guidance 252 1) make it clear who does what: if A sends too many prefixes to B A 253 should see "ABC" in log B should see "DEF" in log to make it clear 254 which of the two parties does what 2) recommended by default 255 automatictly restart after between 15 and 30 minutes 257 12. References 259 12.1. Normative References 261 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 262 Requirement Levels", BCP 14, RFC 2119, 263 DOI 10.17487/RFC2119, March 1997, 264 . 266 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 267 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 268 DOI 10.17487/RFC4271, January 2006, 269 . 271 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 272 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 273 May 2017, . 275 12.2. Informative References 277 [RFC5424] Gerhards, R., "The Syslog Protocol", RFC 5424, 278 DOI 10.17487/RFC5424, March 2009, 279 . 281 [RFC7908] Sriram, K., Montgomery, D., McPherson, D., Osterweil, E., 282 and B. Dickson, "Problem Definition and Classification of 283 BGP Route Leaks", RFC 7908, DOI 10.17487/RFC7908, June 284 2016, . 286 [RIPE77] Snijders, "Robust Routing Policy Architecture", May 2018, 287 . 290 Authors' Addresses 292 Job Snijders 293 NTT Communications 294 Theodorus Majofskistraat 100 295 Amsterdam 1065 SZ 296 The Netherlands 298 Email: job@ntt.net 300 Melchior Aelmans 301 Juniper Networks 302 Boeing Avenue 240 303 Schiphol-Rijk 1119 PZ 304 The Netherlands 306 Email: maelmans@juniper.net