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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reference: RFC 5246 (Obsoleted by RFC 8446) ** Obsolete normative reference: RFC 6536 (Obsoleted by RFC 8341) == Outdated reference: A later version (-09) exists of draft-ietf-idr-rs-bfd-08 Summary: 2 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group E. Chen 3 Internet-Draft Cisco Systems 4 Intended status: Standards Track N. Shen 5 Expires: January 29, 2021 Zededa 6 R. Raszuk 7 Bloomberg LP 8 R. Rahman 9 Cisco Systems 10 July 28, 2020 12 Unsolicited BFD for Sessionless Applications 13 draft-ietf-bfd-unsolicited-02 15 Abstract 17 For operational simplification of "sessionless" applications using 18 BFD, in this document we present procedures for "unsolicited BFD" 19 that allow a BFD session to be initiated by only one side, and be 20 established without explicit per-session configuration or 21 registration by the other side (subject to certain per-interface or 22 per-router policies). 24 Requirements Language 26 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 27 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 28 "OPTIONAL" in this document are to be interpreted as described in BCP 29 14 [RFC2119] [RFC8174] when, and only when, they appear in all 30 capitals, as shown here. 32 Status of This Memo 34 This Internet-Draft is submitted in full conformance with the 35 provisions of BCP 78 and BCP 79. 37 Internet-Drafts are working documents of the Internet Engineering 38 Task Force (IETF). Note that other groups may also distribute 39 working documents as Internet-Drafts. The list of current Internet- 40 Drafts is at https://datatracker.ietf.org/drafts/current/. 42 Internet-Drafts are draft documents valid for a maximum of six months 43 and may be updated, replaced, or obsoleted by other documents at any 44 time. It is inappropriate to use Internet-Drafts as reference 45 material or to cite them other than as "work in progress." 47 This Internet-Draft will expire on January 29, 2021. 49 Copyright Notice 51 Copyright (c) 2020 IETF Trust and the persons identified as the 52 document authors. All rights reserved. 54 This document is subject to BCP 78 and the IETF Trust's Legal 55 Provisions Relating to IETF Documents 56 (https://trustee.ietf.org/license-info) in effect on the date of 57 publication of this document. Please review these documents 58 carefully, as they describe your rights and restrictions with respect 59 to this document. Code Components extracted from this document must 60 include Simplified BSD License text as described in Section 4.e of 61 the Trust Legal Provisions and are provided without warranty as 62 described in the Simplified BSD License. 64 Table of Contents 66 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 67 2. Procedures for Unsolicited BFD . . . . . . . . . . . . . . . 3 68 3. YANG Data Model . . . . . . . . . . . . . . . . . . . . . . . 4 69 3.1. Unsolicited BFD Hierarchy . . . . . . . . . . . . . . . . 4 70 3.2. Unsolicited BFD Module . . . . . . . . . . . . . . . . . 5 71 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 72 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 73 5.1. BFD Protocol Security Considerations . . . . . . . . . . 9 74 5.2. YANG Module Security Considerations . . . . . . . . . . . 9 75 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 76 6.1. Normative References . . . . . . . . . . . . . . . . . . 10 77 6.2. Informative References . . . . . . . . . . . . . . . . . 11 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 80 1. Introduction 82 The current implementation and deployment practice for BFD ([RFC5880] 83 and [RFC5881]) usually requires BFD sessions be explicitly configured 84 or registered on both sides. This requirement is not an issue when 85 an application like BGP [RFC4271] has the concept of a "session" that 86 involves both sides for its establishment. However, this requirement 87 can be operationally challenging when the prerequisite "session" does 88 not naturally exist between two endpoints in an application. 89 Simultaneous configuration and coordination may be required on both 90 sides for BFD to take effect. For example: 92 o When BFD is used to keep track of the "liveness" of the nexthop of 93 static routes. Although only one side may need the BFD 94 functionality, currently both sides need to be involved in 95 specific configuration and coordination and in some cases static 96 routes are created unnecessarily just for BFD. 98 o When BFD is used to keep track of the "liveness" of the third-pary 99 nexthop of BGP routes received from the Route Server [RFC7947] at 100 an Internet Exchange Point (IXP). As the third-party nexthop is 101 different from the peering address of the Route Server, for BFD to 102 work, currently two routers peering with the Route Server need to 103 have routes and nexthops from each other (although indirectly via 104 the Router Server), and the nexthop of each router must be present 105 at the same time. These issues are also discussed in 106 [I-D.ietf-idr-rs-bfd]. 108 Clearly it is beneficial and desirable to reduce or eliminate 109 unnecessary configurations and coordination in these "sessionless" 110 applications using BFD. 112 In this document we present procedures for "unsolicited BFD" that 113 allow a BFD session to be initiated by only one side, and be 114 established without explicit per-session configuration or 115 registration by the other side (subject to certain per-interface or 116 per-router policies). 118 With "unsolicited BFD" there is potential risk for excessive resource 119 usage by BFD from "unexpected" remote systems. To mitigate such 120 risks, several mechanisms are recommended in the Security 121 Considerations section. 123 Compared to the "Seamless BFD" [RFC7880], this proposal involves only 124 minor procedural enhancements to the widely deployed BFD itself. 125 Thus we believe that this proposal is inherently simpler in the 126 protocol itself and deployment. As an example, it does not require 127 the exchange of BFD discriminators over an out-of-band channel before 128 the BFD session bring-up. 130 When BGP Add-Path [RFC7911] is deployed at an IXP using the Route 131 Server, multiple BGP paths (when exist) can be made available to the 132 clients of the Router Server as described in [RFC7947]. The 133 "unsolicited BFD" can be used in BGP route selection by these clients 134 to eliminate paths with "inaccessible nexthops". 136 2. Procedures for Unsolicited BFD 138 With "unsolicited BFD", one side takes the "Active role" and the 139 other side takes only the "Passive role" as described in [RFC5880]. 141 On the passive side, the "unsolicited BFD" SHOULD be configured 142 explicitly on an interface. The BFD parameters can be either per- 143 interface or per-router based. It MAY also choose to use the 144 parameters that the active side uses in its BFD Control packets. The 145 "Discriminator", however, MUST be chosen to allow multiple 146 unsolicited BFD sessions. 148 The active side initiates the BFD Control packets as specified in 149 [RFC5880]. The passive side does not initiates the BFD Control 150 packets. 152 When the passive side receives a BFD Control packet from the active 153 side with 0 as the "remote-discriminator", and it does not find an 154 existing session with the same source address as in the packet and 155 "unsolicited BFD" is allowed on the interface by local policy, it 156 SHOULD then create a matching BFD session toward the active side 157 (based on the source address and destination address in the BFD 158 Control packet) as if the session were locally registered. It would 159 then start sending the BFD Control packets and perform necessary 160 procedure for bringing up, maintaining and tearing down the BFD 161 session. If the BFD session fails to get established within certain 162 specified time, or if an established BFD session goes down, the 163 passive side would stop sending BFD Control packets and delete the 164 BFD session created until the BFD Control packets is initiated by the 165 active side again. 167 The "Passive role" may change to the "Active role" when a local 168 client registers for the same BFD session, and from the "Active role 169 " to the "Passive role " when there is no longer any locally 170 registered client for the BFD session. 172 3. YANG Data Model 174 This section extends the YANG data model for BFD [I-D.ietf-bfd-yang] 175 to cover the unsolicited BFD. 177 3.1. Unsolicited BFD Hierarchy 178 module: ietf-bfd-unsolicited 179 augment /rt:routing/rt:control-plane-protocols 180 /rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh: 181 +--rw unsolicited {bfd-unsol:unsolicited-params-global}? 182 +--rw enable? boolean 183 +--rw local-multiplier? multiplier 184 +--rw (interval-config-type)? 185 +--:(tx-rx-intervals) 186 | +--rw desired-min-tx-interval? uint32 187 | +--rw required-min-rx-interval? uint32 188 +--:(single-interval) {single-minimum-interval}? 189 +--rw min-interval? uint32 190 augment /rt:routing/rt:control-plane-protocols 191 /rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh 192 /bfd-ip-sh:interfaces: 193 +--rw unsolicited {bfd-unsol:unsolicited-params-per-interface}? 194 +--rw enable? boolean 195 +--rw local-multiplier? multiplier 196 +--rw (interval-config-type)? 197 +--:(tx-rx-intervals) 198 | +--rw desired-min-tx-interval? uint32 199 | +--rw required-min-rx-interval? uint32 200 +--:(single-interval) {single-minimum-interval}? 201 +--rw min-interval? uint32 202 augment /rt:routing/rt:control-plane-protocols 203 /rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh 204 /bfd-ip-sh:sessions/bfd-ip-sh:session: 205 +--ro unsolicited 206 +--ro role? bfd-unsol:unsolicited-role 208 3.2. Unsolicited BFD Module 210 file "ietf-bfd-unsolicited@2019-06-26.yang" 212 module ietf-bfd-unsolicited { 214 yang-version 1.1; 216 namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-unsolicited"; 218 prefix "bfd-unsol"; 220 // RFC Ed.: replace occurences of XXXX/YYYY with actual RFC numbers 221 // and remove this note 223 import ietf-bfd-types { 224 prefix "bfd-types"; 225 reference "RFC XXXX: YANG Data Model for BFD"; 226 } 228 import ietf-bfd { 229 prefix "bfd"; 230 reference "RFC XXXX: YANG Data Model for BFD"; 231 } 233 import ietf-bfd-ip-sh { 234 prefix "bfd-ip-sh"; 235 reference "RFC XXXX: YANG Data Model for BFD"; 236 } 238 import ietf-routing { 239 prefix "rt"; 240 reference 241 "RFC 8349: A YANG Data Model for Routing Management 242 (NMDA version)"; 243 } 245 organization "IETF BFD Working Group"; 247 contact 248 "WG Web: 249 WG List: 251 Editors: Enke Chen (enkechen@cisco.com), 252 Naiming Shen (naiming@cisco.com), 253 Robert Raszuk (robert@raszuk.net), 254 Reshad Rahman (rrahman@cisco.com)"; 256 description 257 "This module contains the YANG definition for BFD unsolicited 258 as per RFC YYYY. 260 Copyright (c) 2018 IETF Trust and the persons 261 identified as authors of the code. All rights reserved. 263 Redistribution and use in source and binary forms, with or 264 without modification, is permitted pursuant to, and subject 265 to the license terms contained in, the Simplified BSD License 266 set forth in Section 4.c of the IETF Trust's Legal Provisions 267 Relating to IETF Documents 268 (http://trustee.ietf.org/license-info). 270 This version of this YANG module is part of RFC XXXX; see 271 the RFC itself for full legal notices."; 273 reference "RFC YYYY"; 275 revision 2019-06-26 { 276 description "Initial revision."; 277 reference "RFC YYYY: A YANG data model for BFD unsolicited"; 278 } 280 /* 281 * Feature definitions 282 */ 283 feature unsolicited-params-global { 284 description 285 "This feature indicates that the server supports global 286 parameters for unsolicited sessions."; 287 } 289 feature unsolicited-params-per-interface { 290 description 291 "This feature indicates that the server supports per-interface 292 parameters for unsolicited sessions."; 293 } 295 /* 296 * Type Definitions 297 */ 298 typedef unsolicited-role { 299 type enumeration { 300 enum unsolicited-active { 301 description "Active role"; 302 } 303 enum unsolicited-passive { 304 description "Passive role"; 305 } 306 } 307 description "Unsolicited role"; 308 } 310 /* 311 * Augments 312 */ 313 augment "/rt:routing/rt:control-plane-protocols/" 314 + "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh" { 315 description 316 "Augmentation for BFD unsolicited parameters"; 317 container unsolicited { 318 if-feature bfd-unsol:unsolicited-params-global; 319 description 320 "BFD unsolicited top level container"; 322 leaf enable { 323 type boolean; 324 default false; 325 description 326 "Enable BFD unsolicited globally for IP single-hop."; 327 } 328 uses bfd-types:base-cfg-parms; 329 } 330 } 332 augment "/rt:routing/rt:control-plane-protocols/" 333 + "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh/" 334 + "bfd-ip-sh:interfaces" { 335 description 336 "Augmentation for BFD unsolicited on IP single-hop interface"; 337 container unsolicited { 338 if-feature bfd-unsol:unsolicited-params-per-interface; 339 description 340 "BFD IP single-hop interface unsolicited top level container"; 341 leaf enable { 342 type boolean; 343 default false; 344 description "Enable BFD unsolicited on this interface."; 345 } 346 uses bfd-types:base-cfg-parms; 347 } 348 } 350 augment "/rt:routing/rt:control-plane-protocols/" 351 + "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh/" 352 + "bfd-ip-sh:sessions/bfd-ip-sh:session" { 353 description 354 "Augmentation for BFD unsolicited on IP single-hop session"; 355 container unsolicited { 356 config false; 357 description 358 "BFD IP single-hop session unsolicited top level container"; 359 leaf role { 360 type bfd-unsol:unsolicited-role; 361 description "Role."; 362 } 363 } 364 } 365 } 367 369 4. IANA Considerations 371 This documents makes no IANA requests. 373 5. Security Considerations 375 5.1. BFD Protocol Security Considerations 377 The same security considerations as those described in [RFC5880] and 378 [RFC5881] apply to this document. With "unsolicited BFD" there is 379 potential risk for excessive resource usage by BFD from "unexpected" 380 remote systems. To mitigate such risks, the following measures are 381 RECOMMENDED: 383 o Limit the feature to specific interfaces, and to a single-hop BFD 384 with "TTL=255" [RFC5082]. In addition make sure the source 385 address of an incoming BFD packet belongs to the subnet of the 386 interface from which the BFD packet is received. 387 o Apply "access control" to allow BFD packets only from certain 388 subnets or hosts. 389 o Deploy the feature only in certain "trustworthy" environment, 390 e.g., at an IXP, or between a provider and its customers. 391 o Adjust BFD parameters as needed for the particular deployment and 392 scale. 393 o Use BFD authentication. 395 5.2. YANG Module Security Considerations 397 The YANG module specified in this document defines a schema for data 398 that is designed to be accessed via network management protocols such 399 as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer 400 is the secure transport layer, and the mandatory-to-implement secure 401 transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer 402 is HTTPS, and the mandatory-to-implement secure transport is TLS 403 [RFC5246]. 405 The NETCONF access control model [RFC6536] provides the means to 406 restrict access for particular NETCONF or RESTCONF users to a 407 preconfigured subset of all available NETCONF or RESTCONF protocol 408 operations and content. 410 There are a number of data nodes defined in this YANG module that are 411 writable/creatable/deletable (i.e., config true, which is the 412 default). These data nodes may be considered sensitive or vulnerable 413 in some network environments. Write operations (e.g., edit-config) 414 to these data nodes without proper protection can have a negative 415 effect on network operations. These are the subtrees and data nodes 416 and their sensitivity/vulnerability: 418 /routing/control-plane-protocols/control-plane-protocol/bfd/ip-sh 419 /unsolicited: 421 o data node "enable" enables creation of unsolicited BFD IP single- 422 hop sessions globally, i.e. on all interfaces. See Section 5.1. 423 o data nodes local-multiplier, desired-min-tx-interval, required- 424 min-rx-interval and min-interval all impact the parameters of the 425 unsolicited BFD IP single-hop sessions. 427 /routing/control-plane-protocols/control-plane-protocol/bfd/ip-sh 428 /interfaces/interface/unsolicited: 430 o data node "enable" enables creation of unsolicited BFD IP single- 431 hop sessions on a specific interface. See Section 5.1. 432 o data nodes local-multiplier, desired-min-tx-interval, required- 433 min-rx-interval and min-interval all impact the parameters of the 434 unsolicited BFD IP single-hop sessions on the interface. 436 Some of the readable data nodes in this YANG module may be considered 437 sensitive or vulnerable in some network environments. It is thus 438 important to control read access (e.g., via get, get-config, or 439 notification) to these data nodes. These are the subtrees and data 440 nodes and their sensitivity/vulnerability: 442 /routing/control-plane-protocols/control-plane-protocol/bfd/ip-sh 443 /sessions/session/unsolicited: access to this information discloses 444 the role of the local system in the creation of the unsolicited BFD 445 session. 447 6. References 449 6.1. Normative References 451 [I-D.ietf-bfd-yang] 452 Rahman, R., Zheng, L., Jethanandani, M., Pallagatti, S., 453 and G. Mirsky, "YANG Data Model for Bidirectional 454 Forwarding Detection (BFD)", draft-ietf-bfd-yang-17 (work 455 in progress), August 2018. 457 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 458 Requirement Levels", BCP 14, RFC 2119, 459 DOI 10.17487/RFC2119, March 1997, 460 . 462 [RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C. 463 Pignataro, "The Generalized TTL Security Mechanism 464 (GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007, 465 . 467 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 468 (TLS) Protocol Version 1.2", RFC 5246, 469 DOI 10.17487/RFC5246, August 2008, 470 . 472 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 473 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 474 . 476 [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 477 (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, 478 DOI 10.17487/RFC5881, June 2010, 479 . 481 [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., 482 and A. Bierman, Ed., "Network Configuration Protocol 483 (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, 484 . 486 [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure 487 Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011, 488 . 490 [RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration 491 Protocol (NETCONF) Access Control Model", RFC 6536, 492 DOI 10.17487/RFC6536, March 2012, 493 . 495 [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF 496 Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, 497 . 499 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 500 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 501 May 2017, . 503 6.2. Informative References 505 [I-D.ietf-idr-rs-bfd] 506 Bush, R., Haas, J., Scudder, J., Nipper, A., and C. 507 Dietzel, "Making Route Servers Aware of Data Link Failures 508 at IXPs", draft-ietf-idr-rs-bfd-08 (work in progress), 509 September 2019. 511 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 512 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 513 DOI 10.17487/RFC4271, January 2006, 514 . 516 [RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S. 517 Pallagatti, "Seamless Bidirectional Forwarding Detection 518 (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016, 519 . 521 [RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder, 522 "Advertisement of Multiple Paths in BGP", RFC 7911, 523 DOI 10.17487/RFC7911, July 2016, 524 . 526 [RFC7947] Jasinska, E., Hilliard, N., Raszuk, R., and N. Bakker, 527 "Internet Exchange BGP Route Server", RFC 7947, 528 DOI 10.17487/RFC7947, September 2016, 529 . 531 Authors' Addresses 533 Enke Chen 534 Cisco Systems 535 560 McCarthy Blvd. 536 Milpitas, CA 95035 537 USA 539 Email: enkechen@cisco.com 541 Naiming Shen 542 Zededa 544 Email: naiming@zededa.com 546 Robert Raszuk 547 Bloomberg LP 548 731 Lexington Ave 549 New York City, NY 10022 550 USA 552 Email: robert@raszuk.net 554 Reshad Rahman 555 Cisco Systems 556 2000 Innovation Drive 557 Kanata, Ontario K2K 3E8 558 Canada 560 Email: rrahman@cisco.com