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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) No issues found here. Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Link State Routing K. Talaulikar 3 Internet-Draft P. Psenak 4 Intended status: Standards Track Cisco Systems, Inc. 5 Expires: January 9, 2020 July 8, 2019 7 OSPF Strict-Mode for BFD 8 draft-ketant-lsr-ospf-bfd-strict-mode-02 10 Abstract 12 This document specifies the extensions to OSPF that enables a router 13 and its neighbor to signal their intention to use Bidirectional 14 Forwarding Detection (BFD) for their adjacency using link-local 15 advertisement between them. The signaling of this BFD enablement, 16 allows the router to block and not allow the establishment of 17 adjacency with its neighbor router until a BFD session is 18 successfully established between them. The document describes this 19 OSPF "strict-mode" of BFD establishment as a prerequisite to 20 adjacency formation. 22 Requirements Language 24 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 25 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 26 "OPTIONAL" in this document are to be interpreted as described in BCP 27 14 [RFC2119] [RFC8174] when, and only when, they appear in all 28 capitals, as shown here. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on January 9, 2020. 47 Copyright Notice 49 Copyright (c) 2019 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 65 2. LLS B-bit Flag . . . . . . . . . . . . . . . . . . . . . . . 3 66 3. Local Interface IPv4 Address TLV . . . . . . . . . . . . . . 4 67 4. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 4 68 4.1. OSPFv3 IPv4 Address-Family Specifics . . . . . . . . . . 6 69 4.2. Graceful Restart Considerations . . . . . . . . . . . . . 6 70 5. Operations & Management Considerations . . . . . . . . . . . 6 71 6. Backward Compatibility . . . . . . . . . . . . . . . . . . . 7 72 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 73 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 74 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 75 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 76 10.1. Normative References . . . . . . . . . . . . . . . . . . 8 77 10.2. Informative References . . . . . . . . . . . . . . . . . 9 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 80 1. Introduction 82 Bidirectional Forwarding Detection (BFD) [RFC5880] enables routers to 83 monitor dataplane connectivity over links between them and to detect 84 faults in the bidirectional path between them. This capability is 85 leveraged by routing protocols like Open Shortest Path First (OSPFv2) 86 [RFC2328] and OSPFv3 [RFC5340] to detect connectivity failures for 87 their adjacencies and trigger the rerouting of traffic around this 88 failure more quickly than their periodic hello messaging based 89 detection mechanism. 91 The use of BFD for monitoring routing protocols adjacencies is 92 described in [RFC5882]. When BFD monitoring is enabled for OSPF 93 adjacencies, the BFD session is bootstrapped based on the neighbor 94 address information discovered by the exchange of OSPF hello 95 messages. Faults in the bidirectional forwarding detected via BFD 96 then result in the bringing down of the OSPF adjacency. Note that it 97 is possible in some failure scenarios for the network to be in a 98 state such that the OSPF adjacency is capable of coming up, but the 99 BFD session cannot be established, and, more particularly, data 100 cannot be forwarded. In certain other scenarios, a degraded or poor 101 quality link may result in OSPF adjacency formation to succeed only 102 to result in BFD session establishment not being successful or the 103 BFD session going down frequently due to its faster detection 104 mechanism. 106 To avoid such situations which result in routing churn in the 107 network, it would be beneficial not to allow OSPF to establish a 108 neighbor adjacency until the BFD session is successfully established 109 and stabilized. However, this would preclude the OSPF operation in 110 an environment in which not all OSPF routers support BFD and are 111 enabled for BFD monitoring. A solution would be to block the 112 establishment of OSPF adjacencies if both systems are willing to 113 establish a BFD session but a BFD session cannot be established. 114 Such a mode of BFD use by OSPF is referred to as "strict-mode" 115 wherein BFD session establishment becomes a prerequisite for OSPF 116 adjacency coming up. 118 This document specifies the OSPF protocol extensions using link-local 119 signaling (LLS) [RFC5613] for a router to indicate to its neighbor 120 the willingness to establish a BFD session in the "strict-mode". It 121 also introduces an extension for OSPFv3 link-local signaling of 122 interface IPv4 address when used for IPv4 address-family (AF) 123 instance to indicate to enable discovery of the IPv4 addresses for 124 BFD session setup. 126 A similar functionality for IS-IS is specified [RFC6213]. 128 2. LLS B-bit Flag 130 A new B-bit is defined in the LLS Type 1 Extended Options and Flags 131 field. This bit is defined for the LLS block included in Hello 132 packets and indicates that BFD is enabled on the link and that the 133 router supports BFD strict-mode. Section 7 describes the position of 134 this new B-bit. 136 A router MUST include the LLS block with the LLS Type 1 Extended 137 Options and Flags TLV with the B-bit set its Hello messages when BFD 138 is enabled on the link. 140 3. Local Interface IPv4 Address TLV 142 The Local Interface IPv4 Address TLV is a new LLS TLV meant for 143 OSPFv3 protocol operations for IPv4 AF instances [RFC5838]. It has 144 following format: 146 0 1 2 3 147 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 148 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 149 | Type | Length | 150 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 151 | Local Interface IPv4 Address | 152 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 154 where: 156 Type: TBD, suggested value 21 158 Length: 4 octet 160 Local Interface IPv4 Address: The primary IPv4 address of the 161 local interface. 163 4. Procedures 165 A router supporting BFD strict-mode advertises this capability 166 through its hello messages as described in Section 2 above. When a 167 router supporting BFD strict-mode, detects a new neighbor router that 168 also supports BFD strict-mode, then it proceeds to establish 169 adjacency with that neighbor as described further in this section. 171 This document updates the OSPF neighbor state machine as described in 172 [RFC2328] specifically the operations related to the Init state as 173 below when BFD strict-mode is used: 175 Init (without BFD strict-mode) 177 In this state, an Hello packet has recently been seen from the 178 neighbor. However, bidirectional communication has not yet been 179 established with the neighbor (i.e., the router itself did not 180 appear in the neighbor's Hello packet). All neighbors in this 181 state (or higher) are listed in the Hello packets sent from the 182 associated interface. 184 Init (with BFD strict-mode) 186 In this state, an Hello packet has recently been seen from the 187 neighbor. However, bidirectional communication has not yet been 188 established with the neighbor (i.e., the router itself did not 189 appear in the neighbor's Hello packet). A BFD session 190 establishment to the neighbor is requested, if not already done 191 (e.g. in the event of transition from 2-way state). All neighbors 192 in higher than Init state and those in Init state with BFD session 193 up are listed in the Hello packets sent from the associated 194 interface. 196 Whenever the neighbor state transitions to Down state, the removal of 197 the BFD session associated with that neighbor SHOULD be requested by 198 OSPF and the session re-setup SHOULD similarly be requested by OSPF 199 after transitioning into Init state. This may result in the deletion 200 and creation of BFD session respectively when OSPF is the only client 201 interested in BFD session to the neighbor address. 203 An implementation MUST NOT wait for BFD session establishment in Init 204 state unless BFD strict-mode is enabled on the router and the 205 specific neighbor indicates BFD strict-mode capability via its Hello 206 messages. When BFD is enabled, but the strict-mode of operation 207 cannot be used, then an implementation SHOULD start the BFD session 208 establishment only in 2-Way or higher state. This makes it possible 209 for router to operate a mix of BFD operation in strict-mode or normal 210 mode across different interfaces or even different neighbors on the 211 same multi-access LAN interface. 213 Once the OSPF state machine has moved beyond the Init state, any 214 change in the B-bit advertised in subsequent Hello messages MUST NOT 215 result in any trigger in either the OSPF adjacency or the BFD session 216 management (i.e. the B-bit is considered only when in the Init 217 state). The disabling of BFD (or BFD strict-mode) on a router would 218 result in its not setting the B-bit in its subsequent Hello messages. 219 The disabling of BFD strict-mode has no change on the BFD operations 220 and would not result in bringing down of any established BFD session. 221 The disabling of BFD would result in the BFD session brought down due 222 to Admin reason and hence would not bring down the OSPF adjacency. 224 When BFD is enabled on an interface over which we already have an 225 existing OSPF adjacency, it would result in the router setting the 226 B-bit in its subsequent Hello messages. If the adjacency is already 227 up (i.e. in its terminal state of Full or 2-way with non-DR routers 228 on a LAN) with a neighbor that also support BFD strict-mode, then an 229 implemantion SHOULD NOT bring this adjacency down and instead use the 230 BFD strict-mode of operations after the next transition into Init 231 state. However, if the adjacency is not up, then an implementation 232 MAY bring such an adjacency down so it can use the BFD strict-mode 233 for its bring up. 235 4.1. OSPFv3 IPv4 Address-Family Specifics 237 The multiple AF support in OSPFv3 [RFC5838] requires the use of IPv6 238 link-local address as source address for hello packets even when 239 forming adjacencies for IPv4 AF instances. In most deployments of 240 OSPFv3 IPv4 AF, it is required that BFD be used to monitor and verify 241 the IPv4 data plane connectivity between the routers on the link and 242 hence the BFD session is setup using IPv4 neighbor addresses. The 243 IPv4 neighbor address on the interface is learnt only later in the 244 adjacency formation phase when the neighbor's Link-LSA is received. 245 This results in the setup of the BFD session either after the 246 adjacency is established or much later in the adjacency formation 247 sequence. 249 To enable the BFD operations in strict-mode, it is necessary for a 250 router to learn it's neighbor's IPv4 link address during the Init 251 state of adjacency formation (ideally when it receives the first 252 hello). The use of the Local Interface IPv4 Address TLV (as defined 253 in Section 3) in the LLS block of the OSPFv3 Hello messages for IPv4 254 AF instances makes this possible. Implementations that support 255 strict-mode of BFD operations for OSPFv3 IPv4 AF instances MUST 256 include the Local Interface IPv4 Address TLV in the LLS block of 257 their hello messages whenever the B-bit is set. A receiver MUST 258 ignore the B-bit (i.e. not operate in BFD strict mode) unless the 259 Local Interface IPv4 Address TLV is present in OSPFv3 Hello message 260 for IPv4 AF instances. 262 4.2. Graceful Restart Considerations 264 An implementation needs to handle scenarios where both graceful 265 restart (GR) and the strict-mode of BFD operations are deployed 266 together. The GR aspects discussed in [RFC5882] also apply with 267 strict-mode of operations. In addition to that, since the OSPF 268 adjacency formation is held up until the BFD session establishment in 269 the strict-mode of operation, the resultant delay in adajcency 270 formation may affect or break the GR based recovery. In such cases, 271 it is RECOMMENDED that the GR timers are setup such that they provide 272 sufficient time to cover for normal BFD session establishment delays. 274 5. Operations & Management Considerations 276 An implementation SHOULD report the BFD session status along with the 277 OSPF Init adjacency state when operating in BFD strict-mode and 278 perform logging operations on state transitions to include the BFD 279 events. This allows an operator to detect scenarios where an OSPF 280 adjacency may be stuck waiting for BFD session establishment. 282 6. Backward Compatibility 284 An implementation MUST support OSPF adjacency formation and 285 operations with a neighbor router that does not advertise the BFD 286 strict-mode capability - both when that neighbor router does not 287 support BFD and when it does support BFD but not in the strict-mode 288 of operation as described in this document. Implementations MAY 289 provide an option to specifically enable BFD operations only in the 290 strict-mode in which case, OSPF adjacency with a neighbor that does 291 not support BFD strict-mode would not be established successfully. 292 Implementations MAY provide an option to disable BFD strict-mode 293 which results in the router not advertising the B-bit and BFD 294 operations being performed in the same way as before this 295 specification. 297 The signaling specified in this document happens at a link-local 298 level between routers on that link. A router which does not support 299 this specification would ignore the B-bit in the LLS block of hello 300 messages from its neighbors and continue to bootstrap BFD sessions, 301 if enabled, without holding back the OSPF adjacency formation. Since 302 the router which does not support this specification would not have 303 set the B-bit in the LLS block of its own hello messages, its 304 neighbor routers that support this specification would not use BFD 305 strict-mode with it. As a result, the behavior would be the same as 306 before this specification. Therefore, there are no backward 307 compatibility related issues or considerations that need to be taken 308 care of when implementing this specification. 310 7. IANA Considerations 312 This specification updates Link Local Signaling TLV Identifiers 313 registry. 315 Following values are requested for allocation: 317 o B-bit from "LLS Type 1 Extended Options and Flags" registry at bit 318 position 0x00000010. 320 o TBD (Suggested value 21) - Local Interface IPv4 Address TLV 322 8. Security Considerations 324 The security considerations for "OSPF Link-Local Signaling" [RFC5613] 325 also apply to the extension described in this document. 326 Inappropriate use of the B-bit in the LLS block of an OSPF hello 327 message could prevent an OSPF adjacency from forming or lead to 328 failure to detect bidirectional forwarding failures. If 329 authentication is being used in the OSPF routing domain 331 [RFC5709][RFC7474], then the Cryptographic Authentication TLV 332 [RFC5613] SHOULD also be used to protect the contents of the LLS 333 block. 335 9. Acknowledgements 337 The authors would like to acknowledge the review and inputs from Acee 338 Lindem, Manish Gupta, Balaji Ganesh and Rajesh M. 340 The authors would like to acknowledge Dylan van Oudheusden for 341 highlighting the problems in using strict-mode for BFD session for 342 IPv4 AF instance with OSPFv3 and Baalajee S for his suggestions on 343 the approach to address it. 345 10. References 347 10.1. Normative References 349 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 350 Requirement Levels", BCP 14, RFC 2119, 351 DOI 10.17487/RFC2119, March 1997, 352 . 354 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 355 DOI 10.17487/RFC2328, April 1998, 356 . 358 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 359 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 360 . 362 [RFC5613] Zinin, A., Roy, A., Nguyen, L., Friedman, B., and D. 363 Yeung, "OSPF Link-Local Signaling", RFC 5613, 364 DOI 10.17487/RFC5613, August 2009, 365 . 367 [RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and 368 R. Aggarwal, "Support of Address Families in OSPFv3", 369 RFC 5838, DOI 10.17487/RFC5838, April 2010, 370 . 372 [RFC5882] Katz, D. and D. Ward, "Generic Application of 373 Bidirectional Forwarding Detection (BFD)", RFC 5882, 374 DOI 10.17487/RFC5882, June 2010, 375 . 377 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 378 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 379 May 2017, . 381 10.2. Informative References 383 [RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M., 384 Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic 385 Authentication", RFC 5709, DOI 10.17487/RFC5709, October 386 2009, . 388 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 389 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 390 . 392 [RFC6213] Hopps, C. and L. Ginsberg, "IS-IS BFD-Enabled TLV", 393 RFC 6213, DOI 10.17487/RFC6213, April 2011, 394 . 396 [RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed., 397 "Security Extension for OSPFv2 When Using Manual Key 398 Management", RFC 7474, DOI 10.17487/RFC7474, April 2015, 399 . 401 Authors' Addresses 403 Ketan Talaulikar 404 Cisco Systems, Inc. 405 India 407 Email: ketant@cisco.com 409 Peter Psenak 410 Cisco Systems, Inc. 411 Apollo Business Center 412 Mlynske nivy 43 413 Bratislava 821 09 414 Slovakia 416 Email: ppsenak@cisco.com