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Cartwright-Cox 5 Intended status: Standards Track 17 October 2021 6 Expires: 20 April 2022 8 Border Gateway Protocol 4 (BGP-4) Send Hold Timer 9 draft-spaghetti-idr-bgp-sendholdtimer-03 11 Abstract 13 This document defines the SendHoldTimer session attribute for the 14 Border Gateway Protocol (BGP) Finite State Machine (FSM). 15 Implementation of a SendHoldTimer should help overcome situations 16 where BGP sessions are not terminated after it has become detectable 17 for the local system that the remote system is not processing BGP 18 messages. For robustness, this document specifies that the local 19 system should close BGP connections and not solely rely on the remote 20 system for session tear down when BGP timers have expired. This 21 document updates RFC4271. 23 Requirements Language 25 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 26 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 27 document are to be interpreted as described in RFC 2119 [RFC2119]. 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at https://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on 20 April 2022. 46 Copyright Notice 48 Copyright (c) 2021 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents (https://trustee.ietf.org/ 53 license-info) in effect on the date of publication of this document. 54 Please review these documents carefully, as they describe your rights 55 and restrictions with respect to this document. Code Components 56 extracted from this document must include Simplified BSD License text 57 as described in Section 4.e of the Trust Legal Provisions and are 58 provided without warranty as described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 63 2. Example of a problematic scenario - RFC EDITOR: REMOVE BEFORE 64 PUBLICATION . . . . . . . . . . . . . . . . . . . . . . . 3 65 3. Specification of the Send Hold Timer . . . . . . . . . . . . 3 66 3.1. Session Attributes . . . . . . . . . . . . . . . . . . . 3 67 3.2. SendHoldTimer_Expires Event Definition . . . . . . . . . 4 68 4. Send Hold Timer Expired Error Handling . . . . . . . . . . . 5 69 5. Implementation status - RFC EDITOR: REMOVE BEFORE 70 PUBLICATION . . . . . . . . . . . . . . . . . . . . . . . 5 71 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 72 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 73 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 74 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 75 9.1. Normative References . . . . . . . . . . . . . . . . . . 6 76 9.2. Informative References . . . . . . . . . . . . . . . . . 7 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 79 1. Introduction 81 This document defines the SendHoldTimer session attribute for the 82 Border Gateway Protocol (BGP) [RFC4271] Finite State Machine (FSM) 83 defined in section 8. 85 Failure to terminate a 'stuck' BGP session can result in Denial Of 86 Service, the subsequent failure to generate and deliver BGP WITHDRAW 87 messages to other BGP peers of the local system is detrimental to all 88 participants of the inter-domain routing system. This phenomena is 89 theorised to have contributed to IP traffic backholing events in 90 global Internet routing system [bgpzombies]. 92 This specification intends to improve this situation by requiring 93 sessions to be terminated if the local system has detected that the 94 remote system cannot possibly have received any BGP messages for the 95 duration of the SendHoldTimer. Through codification of the 96 aforementioned requirement, operators will benefit from consistent 97 behavior across different BGP implementations. 99 BGP speakers following this specification do not exclusively rely on 100 remote systems robustly closing connections, but will also locally 101 close connections. 103 2. Example of a problematic scenario - RFC EDITOR: REMOVE BEFORE 104 PUBLICATION 106 A malfunctioning or overwhelmed peer may cause data on the BGP socket 107 in the local system to back up, and the current RFC specification 108 will not cause the session to be torn down. For example, as BGP runs 109 over TCP [RFC0793] it is possible for hosts in the ESTABLISHED state 110 to encounter a BGP peer that is advertising a TCP Receive Window 111 (RCV.WND) of size zero and thus preventing the local system from 112 sending KEEPALIVE, CEASE, WITHDRAW, UPDATE, or other critical 113 messages across the wire. At the moment of writing, most BGP 114 implementations appear unable to handle this situation in a robust 115 fashion. 117 Generally BGP implementation have no visibility into lower-layer 118 subsystems such as TCP or the peer's current Receive Window. 119 Therefor this document banks on BGP implementations being able to 120 detect an inability to push more data to the remote peer, at which 121 point the SendHoldTimer starts. 123 3. Specification of the Send Hold Timer 125 BGP speakers are implemented following a conceptual model "BGP Finite 126 State Machine" (FSM), which is outlined in section 8 of [RFC4271]. 127 This specification updates the BGP FSM as following: 129 3.1. Session Attributes 131 The following mandatory session attributes are added to paragraph 6 132 of Section 8, before "The state session attribute indicates the 133 current state of the BGP FSM": 135 9) SendHoldTimer 137 10) SendHoldTime (an initial value of 4 minutes is recommended) 139 3.2. SendHoldTimer_Expires Event Definition 141 Section 8.1.3 [RFC4271] is extended as following: 143 Event XX: SendHoldTimer_Expires 144 Definition : An event generated when the SendHoldTimer expires. 145 Status: Mandatory 147 If the SendHoldTimer_Expires (Event XX), the local system: 149 - logs a message with the BGP Error Notification Code "Send Hold 150 Timer Expired", 152 - releases all BGP resources, 154 - sets the ConnectRetryTimer to zero, 156 - drops the TCP connection, 158 - increments the ConnectRetryCounter, 160 - (optionally) performs peer oscillation damping if the 161 DampPeerOscillations attribute is set to TRUE, and 163 - changes its state to Idle. 165 If the DelayOpenTimer_Expires event (Event 12) occurs in the Connect 166 state, the local system: 168 - sends an OPEN message to its peer, 170 - sets the HoldTimer to a large value, and 172 - sets the SendHoldTimer to a large value, and 174 - changes its state to OpenSent. 176 If the DelayOpen attribute is set to FALSE, the local system: 178 - stops the ConnectRetryTimer (if running) and sets the 179 ConnectRetryTimer to zero, 181 - completes BGP initialization 183 - sends an OPEN message to its peer, 185 - sets the HoldTimer to a large value, and 186 - sets the SendHoldTimer to a large value, and 188 - changes its state to OpenSent. 190 A HoldTimer value of 4 minutes is suggested. 192 A SendHoldTimer value of 4 minutes is suggested. 194 4. Send Hold Timer Expired Error Handling 196 If a system does not send and receive successive KEEPALIVE, UPDATE, 197 and/or NOTIFICATION messages within the period specified in the Send 198 Hold Time, then the BGP connection is closed and a log message is 199 emitted. 201 5. Implementation status - RFC EDITOR: REMOVE BEFORE PUBLICATION 203 This section records the status of known implementations of the 204 protocol defined by this specification at the time of posting of this 205 Internet-Draft, and is based on a proposal described in RFC 7942. 206 The description of implementations in this section is intended to 207 assist the IETF in its decision processes in progressing drafts to 208 RFCs. Please note that the listing of any individual implementation 209 here does not imply endorsement by the IETF. Furthermore, no effort 210 has been spent to verify the information presented here that was 211 supplied by IETF contributors. This is not intended as, and must not 212 be construed to be, a catalog of available implementations or their 213 features. Readers are advised to note that other implementations may 214 exist. 216 According to RFC 7942, "this will allow reviewers and working groups 217 to assign due consideration to documents that have the benefit of 218 running code, which may serve as evidence of valuable experimentation 219 and feedback that have made the implemented protocols more mature. 220 It is up to the individual working groups to use this information as 221 they see fit". 223 * OpenBGPD [openbgpd] 225 6. Acknowledgements 227 The authors would like to thank William McCall and Theo de Raadt for 228 their helpful review of this document. 230 7. Security Considerations 232 This specification addresses the vulnerability of a BGP speaker to a 233 potential attack whereby a BGP peer can pretend to be unable to 234 process BGP messages and in doing so create a scenario where the 235 local system is poisoned with stale routing information. 237 There are three detrimental aspects to the problem of not robustly 238 handling 'stuck' peers: 240 * Failure to send BGP messages to a peer implies the peer is 241 operating based on stale routing information. 243 * Failure to disconnect from a 'stuck' peer hinders the local 244 system's ability to construct a non-stale local Routing 245 Information Base (RIB). 247 * Failure to disconnect from a 'stuck' peer hinders the local 248 system's ability to inform other BGP peers with current network 249 reachability information. 251 In other respects, this specification does not change BGP's security 252 characteristics. 254 8. IANA Considerations 256 This document requests IANA to assign a value named "Send Hold Timer 257 Expired" in the "BGP Error (Notification) Codes" sub-registry under 258 the "Border Gateway Protocol (BGP) Parameters" registry. 260 9. References 262 9.1. Normative References 264 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 265 RFC 793, DOI 10.17487/RFC0793, September 1981, 266 . 268 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 269 Requirement Levels", BCP 14, RFC 2119, 270 DOI 10.17487/RFC2119, March 1997, 271 . 273 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 274 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 275 DOI 10.17487/RFC4271, January 2006, 276 . 278 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 279 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 280 May 2017, . 282 9.2. Informative References 284 [bgpzombies] 285 Fontugne, R., "BGP Zombies", April 2019, 286 . 289 [openbgpd] Jeker, C., "bgpd send side hold timer", December 2020, 290 . 292 Authors' Addresses 294 Job Snijders 295 Fastly 296 Amsterdam 297 Netherlands 299 Email: job@fastly.com 301 Ben Cartwright-Cox 302 London 303 United Kingdom 305 Email: ben@benjojo.co.uk