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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 8203 (Obsoleted by RFC 9003) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force K. Patel 3 Internet-Draft Arrcus 4 Updates: 4724 (if approved) R. Fernando 5 Intended status: Standards Track Cisco Systems 6 Expires: October 8, 2018 J. Scudder 7 J. Haas 8 Juniper Networks 9 April 6, 2018 11 Notification Message support for BGP Graceful Restart 12 draft-ietf-idr-bgp-gr-notification-14.txt 14 Abstract 16 The BGP Graceful Restart mechanism defined in RFC 4724 limits the 17 usage of BGP Graceful Restart to BGP protocol messages other than a 18 BGP NOTIFICATION message. This document updates RFC 4724 by defining 19 an extension that permits the Graceful Restart procedures to be 20 performed when the BGP speaker receives a BGP NOTIFICATION Message or 21 the Hold Time expires. This document also defines a new BGP 22 NOTIFICATION Cease Error subcode whose effect is to request a full 23 session restart instead of a Graceful Restart. 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 October 8, 2018. 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 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 61 2. Modifications to BGP Graceful Restart Capability . . . . . . 3 62 3. BGP Hard Reset Subcode . . . . . . . . . . . . . . . . . . . 3 63 3.1. Sending a Hard Reset . . . . . . . . . . . . . . . . . . 4 64 3.2. Receiving a Hard Reset . . . . . . . . . . . . . . . . . 4 65 4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 4 66 4.1. Rules for the Receiving Speaker . . . . . . . . . . . . . 5 67 5. Use of Hard Reset . . . . . . . . . . . . . . . . . . . . . . 6 68 5.1. When to Send Hard Reset . . . . . . . . . . . . . . . . . 6 69 5.2. Interaction With Other Specifications . . . . . . . . . . 7 70 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 71 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 72 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 73 9. Normative References . . . . . . . . . . . . . . . . . . . . 8 74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 76 1. Introduction 78 For many classes of errors, the BGP protocol must send a NOTIFICATION 79 message and reset the peering session to handle the error condition. 80 The BGP Graceful Restart extension defined in [RFC4724] requires that 81 normal BGP procedures defined in [RFC4271] be followed when a 82 NOTIFICATION message is sent or received. This document defines an 83 extension to BGP Graceful Restart that permits the Graceful Restart 84 procedures to be performed when the BGP speaker receives a 85 NOTIFICATION message or the Hold Time expires. This permits the BGP 86 speaker to avoid flapping reachability and continue forwarding while 87 the BGP speaker restarts the session to handle errors detected in the 88 BGP protocol. 90 At a high level, this document can be summed up as follows. When a 91 BGP session is reset, both speakers operate as "Receiving Speakers" 92 according to [RFC4724], meaning they retain each other's routes. 93 This is also true for HOLDTIME expiration. The functionality can be 94 defeated using a "Hard Reset" subcode for the BGP NOTIFICATION Cease 95 Error code. If a Hard Reset is used, a full session reset is 96 performed. 98 1.1. Requirements Language 100 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 101 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 102 document are to be interpreted as described in RFC 2119 [RFC2119]. 104 2. Modifications to BGP Graceful Restart Capability 106 The BGP Graceful Restart Capability is augmented to signal the 107 Graceful Restart support for BGP NOTIFICATION messages. The Restart 108 Flags field is augmented as follows (following the diagram from 109 section 3 of [RFC4724]): 111 Restart Flags: 113 This field contains bit flags relating to restart. 115 0 1 2 3 116 +-+-+-+-+ 117 |R|N| | 118 +-+-+-+-+ 120 The most significant ("Restart State", or "R") bit is defined in 121 [RFC4724]. 123 The second most significant bit ("N") is defined as the BGP Graceful 124 Notification bit, which is used to indicate Graceful Restart support 125 for BGP NOTIFICATION messages. A BGP speaker indicates support for 126 the procedures of this document, by advertising a Graceful Restart 127 Capability with its Graceful NOTIFICATION bit set (value 1). This 128 also implies support for the format for a BGP NOTIFICATION Cease 129 message defined in [RFC4486]. 131 If a BGP speaker which previously advertised the "N" bit opens a new 132 session without advertising that bit, normal BGP Graceful Restart 133 procedures documented in [RFC4724] apply. 135 3. BGP Hard Reset Subcode 137 We define a new BGP NOTIFICATION Cease message subcode, called the 138 BGP Hard Reset Subcode. The value of this subcode is discussed in 139 Section 7. We refer to a BGP NOTIFICATION Cease message with the 140 Hard Reset subcode as a Hard Reset message, or just a Hard Reset. 142 When the "N" bit has been exchanged by two peers, to distinguish them 143 from Hard Reset we refer to any NOTIFICATION messages other than Hard 144 Reset as "Graceful", since such messages invoke Graceful Restart 145 semantics. 147 3.1. Sending a Hard Reset 149 A Hard Reset message is used to indicate to a peer with which the 150 Graceful Notification bit has been exchanged, that the session is to 151 be fully terminated. 153 When sending a Hard Reset, the data portion of the NOTIFICATION is 154 encoded as follows: 156 +--------+--------+-------- 157 | ErrCode| Subcode| Data 158 +--------+--------+-------- 160 ErrCode is a BGP Error Code (as documented in the IANA BGP Error 161 Codes registry) that indicates the reason for the Hard Reset. 162 Subcode is a BGP Error Subcode (as documented in the IANA BGP Error 163 Subcodes registry) as appropriate for the ErrCode. Similarly, Data 164 is as appropriate for the ErrCode and Subcode. In short, the Hard 165 Reset encapsulates another NOTIFICATION message in its data portion. 167 3.2. Receiving a Hard Reset 169 Whenever a BGP speaker receives a Hard Reset, the speaker MUST 170 terminate the BGP session following the standard procedures in 171 [RFC4271]. 173 4. Operation 175 A BGP speaker that is willing to receive and send BGP NOTIFICATION 176 messages according to the procedures of this document MUST advertise 177 the BGP Graceful Notification "N" bit using the Graceful Restart 178 Capability as defined in [RFC4724]. 180 When such a BGP speaker has received the "N" bit from its peer, and 181 receives from that peer a BGP NOTIFICATION message other than a Hard 182 Reset, it MUST follow the rules for the Receiving Speaker mentioned 183 in Section 4.1. The BGP speaker generating the BGP NOTIFICATION 184 message MUST also follow the rules for the Receiving Speaker. 186 When a BGP speaker resets its session due to a HOLDTIME expiry, it 187 should generate the relevant BGP NOTIFICATION message as mentioned in 188 [RFC4271], but subsequently it MUST follow the rules for the 189 Receiving Speaker mentioned in Section 4.1. 191 A BGP speaker SHOULD NOT send a Hard Reset to a peer from which it 192 has not received the "N" bit. We note, however, that if it did so 193 the effect would be as desired in any case, since according to 194 [RFC4271] and [RFC4724] any NOTIFICATION message, whether recognized 195 or not, results in a session reset. Thus the only negative effect to 196 be expected from sending the Hard Reset to a peer that hasn't 197 advertised compliance to this specification would be that the peer 198 would be unable to properly log the associated information. 200 Once the session is re-established, both BGP speakers SHOULD set 201 their "Forwarding State" bit to 1. If the "Forwarding State" bit is 202 not set, then according to the procedures of [RFC4724] section 4.2, 203 the relevant routes will be flushed, defeating the goals of this 204 specification. 206 4.1. Rules for the Receiving Speaker 208 [RFC4724] section 4.2 defines rules for the Receiving Speaker. These 209 are modified as follows. 211 The sentence "To deal with possible consecutive restarts, a route 212 (from the peer) previously marked as stale MUST be deleted" only 213 applies when the "N" bit has not been exchanged with the peer: 215 OLD: When the Receiving Speaker detects termination of the TCP 216 session for a BGP session with a peer that has advertised the 217 Graceful Restart Capability, it MUST retain the routes received 218 from the peer for all the address families that were previously 219 received in the Graceful Restart Capability and MUST mark them 220 as stale routing information. To deal with possible consecutive 221 restarts, a route (from the peer) previously marked as stale 222 MUST be deleted. The router MUST NOT differentiate between 223 stale and other routing information during forwarding. 225 NEW: When the Receiving Speaker detects termination of the TCP 226 session for a BGP session with a peer that has advertised the 227 Graceful Restart Capability, it MUST retain the routes received 228 from the peer for all the address families that were previously 229 received in the Graceful Restart Capability and MUST mark them 230 as stale routing information. The router MUST NOT differentiate 231 between stale and other routing information during forwarding. 232 If the "N" bit has not been exchanged with the peer, then to 233 deal with possible consecutive restarts, a route (from the peer) 234 previously marked as stale MUST be deleted. 236 The stale timer is given a formal name and made mandatory: 238 OLD: To put an upper bound on the amount of time a router retains the 239 stale routes, an implementation MAY support a (configurable) 240 timer that imposes this upper bound. 242 NEW: To put an upper bound on the amount of time a router retains the 243 stale routes, an implementation MUST support a (configurable) 244 timer, called the "stale timer", that imposes this upper bound. 245 A suggested default value for the stale timer is 180 seconds. 246 An implementation MAY provide the option to disable the timer 247 (i.e., to provide an infinite retention time) but MUST NOT do so 248 by default. 250 5. Use of Hard Reset 252 5.1. When to Send Hard Reset 254 Although when to send a Hard Reset is an implementation-specific 255 decision, we offer some advice. Many Cease notification subcodes 256 represent permanent or long-term rather than transient session 257 termination, and as such it's appropriate to use Hard Reset with 258 them. At time of publication, Cease subcodes 1-9 were defined. 260 +-------+------------------------------------+----------------------+ 261 | Value | Name | Suggested Behavior | 262 +-------+------------------------------------+----------------------+ 263 | 1 | Maximum Number of Prefixes Reached | Hard Reset | 264 | 2 | Administrative Shutdown | Hard Reset | 265 | 3 | Peer De-configured | Hard Reset | 266 | 4 | Administrative Reset | Provide user control | 267 | 5 | Connection Rejected | Graceful Cease | 268 | 6 | Other Configuration Change | Graceful Cease | 269 | 7 | Connection Collision Resolution | Graceful Cease | 270 | 8 | Out of Resources | Graceful Cease | 271 | 9 | Hard Reset | Hard Reset | 272 +-------+------------------------------------+----------------------+ 274 Suggestions for Cease Subcode Behavior 276 These suggestions are only that, suggestions, not requirements. It's 277 the nature of BGP implementations that the mapping of internal states 278 to BGP NOTIFICATION codes and subcodes is not always perfect. The 279 guiding principle for the implementor should be that if there is no 280 realistic hope that forwarding can continue or that the session will 281 be re-established within the deadline, Hard Reset should be used. 283 For all other NOTIFICATION codes other than Cease, use of Hard Reset 284 does not appear to be indicated. 286 5.2. Interaction With Other Specifications 288 "BGP Administrative Shutdown Communication" [RFC8203] specifies use 289 of the data portion of the Administrative Shutdown or Administrative 290 Reset Cease to convey a short message. When [RFC8203] is used in 291 conjunction with Hard Reset, the subcode of the outermost Cease MUST 292 be Hard Reset, with the Administrative Shutdown or Reset Cease 293 encapsulated within. The encapsulated administrative shutdown 294 message MUST subsequently be processed according to [RFC8203]. 296 6. Acknowledgements 298 The authors would like to thank Jim Uttaro for the suggestion, and 299 Emmanuel Baccelli, Bruno Decraene, Chris Hall, Paul Mattes, Robert 300 Raszuk, and Alvaro Retana for their review and comments. 302 7. IANA Considerations 304 IANA has temporarily assigned subcode 9, named "Hard Reset", in the 305 "BGP Cease NOTIFICATION message subcodes" registry. Upon publication 306 of this document as an RFC, IANA is requested to make this allocation 307 permanent. 309 IANA is requested to establish a registry within the "Border Gateway 310 Protocol (BGP) Parameters" grouping, to be called "BGP Graceful 311 Restart Flags". The Registration Procedure should be Standards 312 Action, the reference this document and [RFC4724], and the initial 313 values as follows: 315 +--------------+---------------+------------+---------------+ 316 | Bit Position | Name | Short Name | Reference | 317 +--------------+---------------+------------+---------------+ 318 | 0 | Restart State | R | [RFC4724] | 319 | 1 | Notification | N | this document | 320 | 2, 3 | unassigned | | | 321 +--------------+---------------+------------+---------------+ 323 IANA is requested to establish a registry within the "Border Gateway 324 Protocol (BGP) Parameters" grouping, to be called "BGP Graceful 325 Restart Flags for Address Family". The Registration Procedure should 326 be Standards Action, the reference this document and [RFC4724], and 327 the initial values as follows: 329 +--------------+------------------+------------+-----------+ 330 | Bit Position | Name | Short Name | Reference | 331 +--------------+------------------+------------+-----------+ 332 | 0 | Forwarding State | F | [RFC4724] | 333 | 1-7 | unassigned | | | 334 +--------------+------------------+------------+-----------+ 336 8. Security Considerations 338 This specification doesn't change the basic security model inherent 339 in [RFC4724], with the exception that the protection against repeated 340 resets is relaxed. To mitigate the consequent risk that an attacker 341 could use repeated session resets to prevent stale routes from ever 342 being deleted, we make the stale routes timer mandatory (in practice 343 it is already ubiquitous). To the extent [RFC4724] might be said to 344 help defend against denials of service by making the control plane 345 more resilient, this extension may modestly increase that resilience; 346 however, there are enough confounding and deployment-specific factors 347 that no general claims can be made. 349 9. Normative References 351 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 352 Requirement Levels", BCP 14, RFC 2119, 353 DOI 10.17487/RFC2119, March 1997, 354 . 356 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 357 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 358 DOI 10.17487/RFC4271, January 2006, 359 . 361 [RFC4486] Chen, E. and V. Gillet, "Subcodes for BGP Cease 362 Notification Message", RFC 4486, DOI 10.17487/RFC4486, 363 April 2006, . 365 [RFC4724] Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y. 366 Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724, 367 DOI 10.17487/RFC4724, January 2007, 368 . 370 [RFC8203] Snijders, J., Heitz, J., and J. Scudder, "BGP 371 Administrative Shutdown Communication", RFC 8203, 372 DOI 10.17487/RFC8203, July 2017, 373 . 375 Authors' Addresses 377 Keyur Patel 378 Arrcus 380 Email: keyur@arrcus.com 382 Rex Fernando 383 Cisco Systems 384 170 W. Tasman Drive 385 San Jose, CA 95134 386 USA 388 Email: rex@cisco.com 390 John Scudder 391 Juniper Networks 392 1194 N. Mathilda Ave 393 Sunnyvale, CA 94089 394 USA 396 Email: jgs@juniper.net 398 Jeff Haas 399 Juniper Networks 400 1194 N. Mathilda Ave 401 Sunnyvale, CA 94089 402 USA 404 Email: jhaas@juniper.net