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Mortensen 3 Internet-Draft Arbor Networks 4 Intended status: Informational R. Moskowitz 5 Expires: January 4, 2018 HTT Consulting 6 T. Reddy 7 McAfee, Inc. 8 July 03, 2017 10 Distributed Denial of Service (DDoS) Open Threat Signaling Requirements 11 draft-ietf-dots-requirements-06 13 Abstract 15 This document defines the requirements for the Distributed Denial of 16 Service (DDoS) Open Threat Signaling (DOTS) protocols coordinating 17 attack response against DDoS attacks. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on January 4, 2018. 36 Copyright Notice 38 Copyright (c) 2017 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 1.1. Context and Motivation . . . . . . . . . . . . . . . . . 2 55 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 56 2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5 57 2.1. General Requirements . . . . . . . . . . . . . . . . . . 7 58 2.2. Signal Channel Requirements . . . . . . . . . . . . . . . 7 59 2.3. Data Channel Requirements . . . . . . . . . . . . . . . . 11 60 2.4. Security requirements . . . . . . . . . . . . . . . . . . 13 61 2.5. Data Model Requirements . . . . . . . . . . . . . . . . . 14 62 3. Congestion Control Considerations . . . . . . . . . . . . . . 15 63 3.1. Signal Channel . . . . . . . . . . . . . . . . . . . . . 15 64 3.2. Data Channel . . . . . . . . . . . . . . . . . . . . . . 15 65 4. Security Considerations . . . . . . . . . . . . . . . . . . . 15 66 5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 16 67 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 68 7. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 16 69 7.1. 04 revision . . . . . . . . . . . . . . . . . . . . . . . 16 70 7.2. 03 revision . . . . . . . . . . . . . . . . . . . . . . . 17 71 7.3. 02 revision . . . . . . . . . . . . . . . . . . . . . . . 17 72 7.4. 01 revision . . . . . . . . . . . . . . . . . . . . . . . 17 73 7.5. 00 revision . . . . . . . . . . . . . . . . . . . . . . . 18 74 7.6. Initial revision . . . . . . . . . . . . . . . . . . . . 18 75 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 76 8.1. Normative References . . . . . . . . . . . . . . . . . . 18 77 8.2. Informative References . . . . . . . . . . . . . . . . . 19 78 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 80 1. Introduction 82 1.1. Context and Motivation 84 Distributed Denial of Service (DDoS) attacks continue to plague 85 network operators around the globe, from Tier-1 service providers on 86 down to enterprises and small businesses. Attack scale and frequency 87 similarly have continued to increase, in part as a result of software 88 vulnerabilities leading to reflection and amplification attacks. 89 Once-staggering attack traffic volume is now the norm, and the impact 90 of larger-scale attacks attract the attention of international press 91 agencies. 93 The greater impact of contemporary DDoS attacks has led to increased 94 focus on coordinated attack response. Many institutions and 95 enterprises lack the resources or expertise to operate on-premises 96 attack mitigation solutions themselves, or simply find themselves 97 constrained by local bandwidth limitations. To address such gaps, 98 security service providers have begun to offer on-demand traffic 99 scrubbing services, which aim to separate the DDoS traffic from 100 legitimate traffic and forward only the latter. Today each such 101 service offers its own interface for subscribers to request attack 102 mitigation, tying subscribers to proprietary signaling 103 implementations while also limiting the subset of network elements 104 capable of participating in the attack response. As a result of 105 signaling interface incompatibility, attack responses may be 106 fragmentary or otherwise incomplete, leaving key players in the 107 attack path unable to assist in the defense. 109 The lack of a common method to coordinate a real-time response among 110 involved actors and network domains inhibits the speed and 111 effectiveness of DDoS attack mitigation. This document describes the 112 required characteristics of a protocol enabling requests for DDoS 113 attack mitigation, reducing attack impact and leading to more 114 efficient defensive strategies. 116 DOTS communicates the need for defensive action in anticipation of or 117 in response to an attack, but does not dictate the form any defensive 118 action takes. DOTS supplements calls for help with pertinent details 119 about the detected attack, allowing entities participating in DOTS to 120 form ad hoc, adaptive alliances against DDoS attacks as described in 121 the DOTS use cases [I-D.ietf-dots-use-cases]. The requirements in 122 this document are derived from those use cases and 123 [I-D.ietf-dots-architecture]. 125 1.2. Terminology 127 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 128 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 129 document are to be interpreted as described in [RFC2119]. 131 This document adopts the following terms: 133 DDoS: A distributed denial-of-service attack, in which traffic 134 originating from multiple sources are directed at a target on a 135 network. DDoS attacks are intended to cause a negative impact on 136 the availability of servers, services, applications, and/or other 137 functionality of an attack target. Denial-of-service 138 considerations are discussed in detail in [RFC4732]. 140 DDoS attack target: A network connected entity with a finite set of 141 resources, such as network bandwidth, memory or CPU, that is the 142 focus of a DDoS attack. Potential targets include network 143 elements, network links, servers, and services. 145 DDoS attack telemetry: Collected measurements and behavioral 146 characteristics defining the nature of a DDoS attack. 148 Countermeasure: An action or set of actions taken to recognize and 149 filter out DDoS attack traffic while passing legitimate traffic to 150 the attack target. 152 Mitigation: A set of countermeasures enforced against traffic 153 destined for the target or targets of a detected or reported DDoS 154 attack, where countermeasure enforcement is managed by an entity 155 in the network path between attack sources and the attack target. 156 Mitigation methodology is out of scope for this document. 158 Mitigator: An entity, typically a network element, capable of 159 performing mitigation of a detected or reported DDoS attack. For 160 the purposes of this document, this entity is a black box capable 161 of mitigation, making no assumptions about availability or design 162 of countermeasures, nor about the programmable interface between 163 this entity and other network elements. The mitigator and DOTS 164 server are assumed to belong to the same administrative entity. 166 DOTS client: A DOTS-aware software module responsible for requesting 167 attack response coordination with other DOTS-aware elements. 169 DOTS server: A DOTS-aware software module handling and responding to 170 messages from DOTS clients. The DOTS server SHOULD enable 171 mitigation on behalf of the DOTS client, if requested, by 172 communicating the DOTS client's request to the mitigator and 173 returning selected mitigator feedback to the requesting DOTS 174 client. A DOTS server MAY also be a mitigator. 176 DOTS agent: Any DOTS-aware software module capable of participating 177 in a DOTS signal or data channel. 179 DOTS gateway: A logical DOTS agent resulting from the logical 180 concatenation of a DOTS server and a DOTS client, analogous to a 181 SIP Back-to-Back User Agent (B2BUA) [RFC3261]. DOTS gateways are 182 discussed in detail in [I-D.ietf-dots-architecture]. 184 Signal channel: A bidirectional, mutually authenticated 185 communication channel between DOTS agents characterized by 186 resilience even in conditions leading to severe packet loss, such 187 as a volumetric DDoS attack causing network congestion. 189 DOTS signal: A concise authenticated status/control message 190 transmitted between DOTS agents, used to indicate client's need 191 for mitigation, as well as to convey the status of any requested 192 mitigation. 194 Heartbeat: A message transmitted between DOTS agents over the signal 195 channel, used as a keep-alive and to measure peer health. 197 Client signal: A message sent from a DOTS client to a DOTS server 198 over the signal channel, indicating the DOTS client's need for 199 mitigation, as well as the scope of any requested mitigation, 200 optionally including additional attack details to supplement 201 server-initiated mitigation. 203 Server signal: A message sent from a DOTS server to a DOTS client 204 over the signal channel. Note that a server signal is not a 205 response to client signal, but a DOTS server-initiated status 206 message sent to DOTS clients with which the server has established 207 signal channels. 209 Data channel: A secure communication layer between DOTS clients and 210 DOTS servers used for infrequent bulk exchange of data not easily 211 or appropriately communicated through the signal channel under 212 attack conditions. 214 Filter: A policy matching a network traffic flow or set of flows and 215 rate-limiting or discarding matching traffic. 217 Blacklist: A filter list of addresses, prefixes and/or other 218 identifiers indicating sources from which traffic should be 219 blocked, regardless of traffic content. 221 Whitelist: A list of addresses, prefixes and/or other identifiers 222 from indicating sources from which traffic should always be 223 allowed, regardless of contradictory data gleaned in a detected 224 attack. 226 Multi-homed DOTS client: A DOTS client exchanging messages with 227 multiple DOTS servers, each in a separate administrative domain. 229 2. Requirements 231 This section describes the required features and characteristics of 232 the DOTS protocol. 234 DOTS is an advisory protocol. An active DDoS attack against the 235 entity controlling the DOTS client need not be present before 236 establishing a communication channel between DOTS agents. Indeed, 237 establishing a relationship with peer DOTS agents during normal 238 network conditions provides the foundation for more rapid attack 239 response against future attacks, as all interactions setting up DOTS, 240 including any business or service level agreements, are already 241 complete. 243 The DOTS protocol must at a minimum make it possible for a DOTS 244 client to request a mitigator's aid mounting a defense, coordinated 245 by a DOTS server, against a suspected attack, signaling within or 246 between domains as requested by local operators. DOTS clients should 247 similarly be able to withdraw aid requests. DOTS requires no 248 justification from DOTS clients for requests for help, nor do DOTS 249 clients need to justify withdrawing help requests: the decision is 250 local to the DOTS clients' domain. 252 Regular feedback between DOTS clients and DOTS server supplement the 253 defensive alliance by maintaining a common understanding of DOTS 254 agent health and activity. Bidirectional communication between DOTS 255 clients and DOTS servers is therefore critical. 257 DOTS protocol implementations face competing operational goals when 258 maintaining this bidirectional communication stream. On the one 259 hand, the protocol must be resilient under extremely hostile network 260 conditions, providing continued contact between DOTS agents even as 261 attack traffic saturates the link. Such resiliency may be developed 262 several ways, but characteristics such as small message size, 263 asynchronous, redundant message delivery and minimal connection 264 overhead (when possible given local network policy) will tend to 265 contribute to the robustness demanded by a viable DOTS protocol. 266 Operators of peer DOTS-enabled domains may enable quality- or class- 267 of-service traffic tagging to increase the probability of successful 268 DOTS signal delivery, but DOTS requires no such policies be in place. 269 The DOTS solution indeed must be viable especially in their absence. 271 On the other hand, DOTS must include protections ensuring message 272 confidentiality, integrity and authenticity to keep the protocol from 273 becoming another vector for the very attacks it's meant to help fight 274 off. DOTS clients must be able to authenticate DOTS servers, and 275 vice versa, to avoid exposing new attack surfaces when deploying 276 DOTS; specifically, to prevent DDoS mitigation in response to DOTS 277 signaling from becoming a new form of attack. In order to provide 278 this level of proteection, DOTS agents must have a way to negotiate 279 and agree upon the terms of protocol security. Attacks against the 280 transport protocol should not offer a means of attack against the 281 message confidentiality, integrity and authenticity. 283 The DOTS server and client must also have some common method of 284 defining the scope of any mitigation performed by the mitigator, as 285 well as making adjustments to other commonly configurable features, 286 such as listen ports, exchanging black- and white-lists, and so on. 288 Finally, DOTS should be sufficiently extensible to meet future needs 289 in coordinated attack defense, although this consideration is 290 necessarily superseded by the other operational requirements. 292 2.1. General Requirements 294 GEN-001 Extensibility: Protocols and data models developed as part 295 of DOTS MUST be extensible in order to keep DOTS adaptable to 296 operational and proprietary DDoS defenses. Future extensions MUST 297 be backward compatible. DOTS protocols MUST use a version number 298 system to distinguish protocol revisions. Implementations of 299 older protocol versions SHOULD ignore information added to DOTS 300 messages as part of newer protocol versions. 302 GEN-002 Resilience and Robustness: The signaling protocol MUST be 303 designed to maximize the probability of signal delivery even under 304 the severely constrained network conditions imposed by particular 305 attack traffic. The protocol MUST be resilient, that is, continue 306 operating despite message loss and out-of-order or redundant 307 message delivery. In support signaling protocol robustness, DOTS 308 signals SHOULD be conveyed over a transport not susceptible to 309 Head of Line Blocking. 311 GEN-003 Bidirectionality: To support peer health detection, to 312 maintain an open signal channel, and to increase the probability 313 of signal delivery during attack, the signal channel MUST be 314 bidirectional, with client and server transmitting signals to each 315 other at regular intervals, regardless of any client request for 316 mitigation. Unidirectional messages MUST be supported within the 317 bidirectional signal channel to allow for unsolicited message 318 delivery, enabling asynchronous notifications between agents. 320 GEN-004 Bulk Data Exchange: Infrequent bulk data exchange between 321 DOTS agents can also significantly augment attack response 322 coordination, permitting such tasks as population of black- or 323 white-listed source addresses; address or prefix group aliasing; 324 exchange of incident reports; and other hinting or configuration 325 supplementing attack response. 327 As the resilience requirements for the DOTS signal channel mandate 328 small signal message size, a separate, secure data channel 329 utilizing a reliable transport protocol MUST be used for bulk data 330 exchange. 332 2.2. Signal Channel Requirements 334 SIG-001 Use of Common Transport Protocols: DOTS MUST operate over 335 common widely deployed and standardized transport protocols. 336 While connectionless transport such as the User Datagram Protocol 337 (UDP) [RFC0768] SHOULD be used for the signal channel, the 338 Transmission Control Protocol (TCP) [RFC0793] MAY be used if 339 necessary due to network policy or middlebox capabilities or 340 configurations. 342 SIG-002 Sub-MTU Message Size: To avoid message fragmentation and the 343 consequently decreased probability of message delivery over a 344 congested link, signaling protocol message size MUST be kept under 345 signaling Path Maximum Transmission Unit (PMTU), including the 346 byte overhead of any encapsulation, transport headers, and 347 transport- or message-level security. 349 DOTS agents SHOULD attempt to learn the PMTU through mechanisms 350 such as Path MTU Discovery [RFC1191] or Packetization Layer Path 351 MTU Discovery [RFC4821]. If the PMTU cannot be discovered, DOTS 352 agents SHOULD assume a PMTU of 1280 bytes. If IPv4 support on 353 legacy or otherwise unusual networks is a consideration and PMTU 354 is unknown, DOTS implementations MAY rely on a PMTU of 576 bytes, 355 as discussed in [RFC0791] and [RFC1122]. 357 SIG-003 Channel Health Monitoring: Peer DOTS agents MUST regularly 358 send heartbeats to each other after mutual authentication in order 359 to keep the DOTS signal channel active. A signal channel MUST be 360 considered active until a DOTS agent explicitly ends the session, 361 or either DOTS agent fails to receive heartbeats from the other 362 after a mutually agreed upon timeout period has elapsed. 364 SIG-004 Channel Redirection: In order to increase DOTS operational 365 flexibility and scalability, DOTS servers SHOULD be able to 366 redirect DOTS clients to another DOTS server at any time. DOTS 367 clients MUST NOT assume the redirection target DOTS server shares 368 security state with the redirecting DOTS server. DOTS clients MAY 369 attempt abbreviated security negotiation methods supported by the 370 protocol, such as DTLS session resumption, but MUST be prepared to 371 negotiate new security state with the redirection target DOTS 372 server. 374 Due to the increased likelihood of packet loss caused by link 375 congestion during an attack, DOTS servers SHOULD NOT redirect 376 while mitigation is enabled during an active attack against a 377 target in the DOTS client's domain. 379 SIG-005 Mitigation Requests and Status: Authorized DOTS clients MUST 380 be able to request scoped mitigation from DOTS servers. DOTS 381 servers MUST send mitigation request status in response to DOTS 382 clients requests for mitigation, and SHOULD accept scoped 383 mitigation requests from authorized DOTS clients. DOTS servers 384 MAY reject authorized requests for mitigation, but MUST include a 385 reason for the rejection in the status message sent to the client. 387 Due to the higher likelihood of packet loss during a DDoS attack, 388 DOTS servers SHOULD regularly send mitigation status to authorized 389 DOTS clients which have requested and been granted mitigation, 390 regardless of client requests for mitigation status. 392 When DOTS client-requested mitigation is active, DOTS server 393 status messages SHOULD include the following mitigation metrics: 395 * Total number of packets blocked by the mitigation 397 * Current number of packets per second blocked 399 * Total number of bytes blocked 401 * Current number of bytes per second blocked 403 DOTS clients MAY take these metrics into account when determining 404 whether to ask the DOTS server to cease mitigation. 406 Once a DOTS client requests mitigation, the client MAY withdraw 407 that request at any time, regardless of whether mitigation is 408 currently active. The DOTS server MUST immediately acknowledge a 409 DOTS client's request to stop mitigation. 411 To protect against route or DNS flapping caused by a client 412 rapidly toggling mitigation, and to dampen the effect of 413 oscillating attacks, DOTS servers MAY allow mitigation to continue 414 for a limited period after acknowledging a DOTS client's 415 withdrawal of a mitigation request. During this period, DOTS 416 server status messages SHOULD indicate that mitigation is active 417 but terminating. 419 The active-but-terminating period is initially 30 seconds. If the 420 client requests mitigation again before that 30 second window 421 elapses, the DOTS server MAY exponentially increase the active- 422 but-terminating period up to a maximum of 240 seconds (4 minutes). 423 After the active-but-terminating period elapses, the DOTS server 424 MUST treat the mitigation as terminated, as the DOTS client is no 425 longer responsible for the mitigation. For example, if there is a 426 financial relationship between the DOTS client and server domains, 427 the DOTS client ceases incurring cost at this point. 429 SIG-006 Mitigation Lifetime: DOTS servers MUST support mitigation 430 lifetimes, and MUST terminate a mitigation when the lifetime 431 elapses. DOTS servers also MUST support renewal of mitigation 432 lifetimes in mitigation requests from DOTS clients, allowing 433 clients to extend mitigation as necessary for the duration of an 434 attack. 436 DOTS servers MUST treat a mitigation terminated due to lifetime 437 expiration exactly as if the DOTS client originating the 438 mitigation had asked to end the mitigation, including the active- 439 but-terminating period, as described above in SIG-005. 441 DOTS clients SHOULD include a mitigation lifetime in all 442 mitigation requests. If a DOTS client does not include a 443 mitigation lifetime in requests for help sent to the DOTS server, 444 the DOTS server will use a reasonable default as defined by the 445 protocol. 447 DOTS servers SHOULD support indefinite mitigation lifetimes, 448 enabling architectures in which the mitigator is always in the 449 traffic path to the resources for which the DOTS client is 450 requesting protection. DOTS servers MAY refuse mitigations with 451 indefinite lifetimes, for policy reasons. The reasons themselves 452 are out of scope for this document, but MUST be included in the 453 mitigation rejection message from the server, per SIG-005. 455 SIG-007 Mitigation Scope: DOTS clients MUST indicate desired 456 mitigation scope. The scope type will vary depending on the 457 resources requiring mitigation. All DOTS agent implementations 458 MUST support the following required scope types: 460 * IPv4 addresses in dotted quad format 462 * IPv4 prefixes in CIDR notation [RFC4632] 464 * IPv6 addresses [RFC4291][RFC5952] 466 * IPv6 prefixes [RFC4291][RFC5952] 468 * Domain names [RFC1035] 470 The following mitigation scope types are OPTIONAL: 472 * Uniform Resource Identifiers [RFC3986] 474 DOTS agents MUST support mitigation scope aliases, allowing DOTS 475 client and server to refer to collections of protected resources 476 by an opaque identifier created through the data channel, direct 477 configuration, or other means. Domain name and URI mitigation 478 scopes may be thought of as a form of scope alias, in which the 479 addresses to which the domain name or URI resolve represent the 480 full scope of the mitigation. 482 If there is additional information available narrowing the scope 483 of any requested attack response, such as targeted port range, 484 protocol, or service, DOTS clients SHOULD include that information 485 in client signals. DOTS clients MAY also include additional 486 attack details. Such supplemental information is OPTIONAL, and 487 DOTS servers MAY ignore it when enabling countermeasures on the 488 mitigator. 490 As an active attack evolves, clients MUST be able to adjust as 491 necessary the scope of requested mitigation by refining the scope 492 of resources requiring mitigation. 494 SIG-008 Mitigation Efficacy: When a mitigation request by a DOTS 495 client is active, DOTS clients SHOULD transmit a metric of 496 perceived mitigation efficacy to the DOTS server. DOTS servers 497 MAY use the efficacy metric to adjust countermeasures activated on 498 a mitigator on behalf of a DOTS client. 500 SIG-009 Conflict Detection and Notification: Multiple DOTS clients 501 controlled by a single administrative entity may send conflicting 502 mitigation requests for pool of protected resources , as a result 503 of misconfiguration, operator error, or compromised DOTS clients. 504 DOTS servers attempting to honor conflicting requests may flap 505 network route or DNS information, degrading the networks 506 attempting to participate in attack response with the DOTS 507 clients. DOTS servers SHALL detect such conflicting requests, and 508 SHALL notify the DOTS clients in conflict. The notification 509 SHOULD indicate the nature and scope of the conflict, for example, 510 the overlapping prefix range in a conflicting mitigation request. 512 SIG-010: Network Address Translator Traversal: DOTS clients may be 513 deployed behind a Network Address Translator (NAT), and need to 514 communicate with DOTS servers through the NAT. DOTS protocols 515 MUST therefore be capable of traversing NATs. 517 If UDP is used as the transport for the DOTS signal channel, all 518 considerations in "Middlebox Traversal Guidelines" in [RFC5405] 519 apply to DOTS. Regardless of transport, DOTS protocols MUST 520 follow established best common practices (BCPs) for NAT traversal. 522 2.3. Data Channel Requirements 524 The data channel is intended to be used for bulk data exchanges 525 between DOTS agents. Unlike the signal channel, which must operate 526 nominally even when confronted with signal degradation due to packet 527 loss, the data channel is not expected to be constructed to deal with 528 attack conditions. As the primary function of the data channel is 529 data exchange, a reliable transport is required in order for DOTS 530 agents to detect data delivery success or failure. 532 The data channel must be extensible. We anticipate the data channel 533 will be used for such purposes as configuration or resource 534 discovery. For example, a DOTS client may submit to the DOTS server 535 a collection of prefixes it wants to refer to by alias when 536 requesting mitigation, to which the server would respond with a 537 success status and the new prefix group alias, or an error status and 538 message in the event the DOTS client's data channel request failed. 539 The transactional nature of such data exchanges suggests a separate 540 set of requirements for the data channel, while the potentially 541 sensitive content sent between DOTS agents requires extra precautions 542 to ensure data privacy and authenticity. 544 DATA-001 Reliable transport: Messages sent over the data channel 545 MUST be delivered reliably, in order sent. 547 DATA-002 Data privacy and integrity: Transmissions over the data 548 channel are likely to contain operationally or privacy-sensitive 549 information or instructions from the remote DOTS agent. Theft or 550 modification of data channel transmissions could lead to 551 information leaks or malicious transactions on behalf of the 552 sending agent (see Section 4 below). Consequently data sent over 553 the data channel MUST be encrypted and authenticated using current 554 industry best practices. DOTS servers MUST enable means to 555 prevent leaking operationally or privacy-sensitive data. Although 556 administrative entities participating in DOTS may detail what data 557 may be revealed to third-party DOTS agents, such considerations 558 are not in scope for this document. 560 DATA-003 Resource Configuration: To help meet the general and signal 561 channel requirements in this document, DOTS server implementations 562 MUST provide an interface to configure resource identifiers, as 563 described in SIG-007. DOTS server implementations MAY expose 564 additional configurability. Additional configurability is 565 implementation-specific. 567 DATA-004 Black- and whitelist management: DOTS servers MUST provide 568 methods for DOTS clients to manage black- and white-lists of 569 traffic destined for resources belonging to a client. 571 For example, a DOTS client should be able to create a black- or 572 whitelist entry; retrieve a list of current entries from either 573 list; update the content of either list; and delete entries as 574 necessary. 576 How the DOTS server authorizes DOTS client management of black- 577 and white-list entries is implementation-specific. 579 2.4. Security requirements 581 DOTS must operate within a particularly strict security context, as 582 an insufficiently protected signal or data channel may be subject to 583 abuse, enabling or supplementing the very attacks DOTS purports to 584 mitigate. 586 SEC-001 Peer Mutual Authentication: DOTS agents MUST authenticate 587 each other before a DOTS signal or data channel is considered 588 valid. The method of authentication is not specified, but should 589 follow current industry best practices with respect to any 590 cryptographic mechanisms to authenticate the remote peer. 592 SEC-002 Message Confidentiality, Integrity and Authenticity: DOTS 593 protocols MUST take steps to protect the confidentiality, 594 integrity and authenticity of messages sent between client and 595 server. While specific transport- and message-level security 596 options are not specified, the protocols MUST follow current 597 industry best practices for encryption and message authentication. 599 In order for DOTS protocols to remain secure despite advancements 600 in cryptanalysis and traffic analysis, DOTS agents MUST be able to 601 negotiate the terms and mechanisms of protocol security, subject 602 to the interoperability and signal message size requirements 603 above. 605 While the interfaces between downstream DOTS server and upstream 606 DOTS client within a DOTS gateway are implementation-specific, 607 those interfaces nevertheless MUST provide security equivalent to 608 that of the signal channels bridged by gateways in the signaling 609 path. For example, when a DOTS gateway consisting of a DOTS 610 server and DOTS client is running on the same logical device, they 611 must be within the same process security boundary. 613 SEC-003 Message Replay Protection: To prevent a passive attacker 614 from capturing and replaying old messages, and thereby potentially 615 disrupting or influencing the network policy of the receiving DOTS 616 agent's domain, DOTS protocols MUST provide a method for replay 617 detection and prevention. 619 Within the signal channel, messages MUST be uniquely identified 620 such that replayed or duplicated messages may be detected and 621 discarded. Unique mitigation requests MUST be processed at most 622 once. 624 SEC-004 Authorization: DOTS servers MUST authorize all messages from 625 DOTS clients which pertain to mitigation, configuration, 626 filtering, or status. 628 DOTS servers MUST reject mitigation requests with scopes which the 629 DOTS client is not authorized to manage. 631 Likewise, DOTS servers MUST refuse to allow creation, modification 632 or deletion of scope aliases and black-/white-lists when the DOTS 633 client is unauthorized. 635 The modes of authorization are implementation-specific. 637 2.5. Data Model Requirements 639 The value of DOTS is in standardizing a mechanism to permit elements, 640 networks or domains under or under threat of DDoS attack to request 641 aid mitigating the effects of any such attack. A well-structured 642 DOTS data model is therefore critical to the development of a 643 successful DOTS protocol. 645 DM-001: Structure: The data model structure for the DOTS protocol 646 may be described by a single module, or be divided into related 647 collections of hierarchical modules and sub-modules. If the data 648 model structure is split across modules, those distinct modules 649 MUST allow references to describe the overall data model's 650 structural dependencies. 652 DM-002: Versioning: To ensure interoperability between DOTS protocol 653 implementations, data models MUST be versioned. The version 654 number of the initial data model SHALL be 1. Each published 655 change to the initial published DOTS data model SHALL increment 656 the data model version by 1. 658 How the protocol represents data model versions is not defined in 659 this document. 661 DM-003: Mitigation Status Representation: The data model MUST 662 provide the ability to represent a request for mitigation and the 663 withdrawal of such a request. The data model MUST also support a 664 representation of currently requested mitigation status, including 665 failures and their causes. 667 DM-004: Mitigation Scope Representation: The data model MUST support 668 representation of a requested mitigation's scope. As mitigation 669 scope may be represented in several different ways, per SIG-007 670 above, the data model MUST be capable of flexible representation 671 of mitigation scope. 673 DM-005: Mitigation Lifetime Representation: The data model MUST 674 support representation of a mitigation request's lifetime, 675 including mitigations with no specified end time. 677 DM-006: Mitigation Efficacy Representation: The data model MUST 678 support representation of a DOTS client's understanding of the 679 efficacy of a mitigation enabled through a mitigation request. 681 DM-007: Acceptable Signal Loss Representation: The data model MUST 682 be able to represent the DOTS agent's preference for acceptable 683 signal loss when establishing a signal channel, as described in 684 GEN-002. 686 DM-008: Heartbeat Interval Representation: The data model MUST be 687 able to represent the DOTS agent's preferred heartbeat interval, 688 which the client may include when establishing the signal channel, 689 as described in SIG-003. 691 DM-009: Relationship to Transport: The DOTS data model MUST NOT 692 depend on the specifics of any transport to represent fields in 693 the model. 695 3. Congestion Control Considerations 697 3.1. Signal Channel 699 As part of a protocol expected to operate over links affected by DDoS 700 attack traffic, the DOTS signal channel MUST NOT contribute 701 significantly to link congestion. To meet the signal channel 702 requirements above, DOTS signal channel implementations SHOULD 703 support connectionless transports. However, some connectionless 704 transports when deployed naively can be a source of network 705 congestion, as discussed in [RFC5405]. Signal channel 706 implementations using such connectionless transports, such as UDP, 707 therefore MUST include a congestion control mechanism. 709 Signal channel implementations using TCP may rely on built-in TCP 710 congestion control support. 712 3.2. Data Channel 714 As specified in DATA-001, the data channel requires reliable, in- 715 order message delivery. Data channel implementations using TCP may 716 rely on the TCP implementation's built-in congestion control 717 mechanisms. 719 4. Security Considerations 721 DOTS is at risk from three primary attacks: 723 o DOTS agent impersonation 724 o Traffic injection 726 o Signaling blocking 728 The DOTS protocol MUST be designed for minimal data transfer to 729 address the blocking risk. Impersonation and traffic injection 730 mitigation can be managed through current secure communications best 731 practices. See Section 2.4 above for a detailed discussion. 733 5. Contributors 735 Mohamed Boucadair 736 Orange 738 mohamed.boucadair@orange.com 740 Flemming Andreasen 741 Cisco Systems, Inc. 743 fandreas@cisco.com 745 Dave Dolson 746 Sandvine 748 ddolson@sandvine.com 750 6. Acknowledgments 752 Thanks to Roman Danyliw and Matt Richardson for careful reading and 753 feedback. 755 7. Change Log 757 7.1. 04 revision 759 2017-03-13 761 o Establish required and optional mitigation scope types 763 o Specify message size for DOTS signal channel 765 o Recast mitigation lifetime as a DOTS server requirement 767 o Clarify DOTS server's responsibilities after client request to end 768 mitigation 770 o Specify security state handling on redirection 771 o Signal channel should use transport not susceptible to HOL 772 blocking 774 o Expanded list of DDoS types to include network links 776 7.2. 03 revision 778 2016-10-30 780 o Extended SEC-003 to require secure interfaces within DOTS 781 gateways. 783 o Changed DATA-003 to Resource Configuration, delegating control of 784 acceptable signal loss, heartbeat intervals, and mitigation 785 lifetime to DOTS client. 787 o Added data model requirements reflecting client control over the 788 above. 790 7.3. 02 revision 792 7.4. 01 revision 794 2016-03-21 796 o Reconciled terminology with -00 revision of 797 [I-D.ietf-dots-use-cases]. 799 o Terminology clarification based on working group feedback. 801 o Moved security-related requirements to separate section. 803 o Made resilience/robustness primary general requirement to align 804 with charter. 806 o Clarified support for unidirectional communication within the 807 bidirectional signal channel. 809 o Added proposed operational requirement to support session 810 redirection. 812 o Added proposed operational requirement to support conflict 813 notification. 815 o Added proposed operational requirement to support mitigation 816 lifetime in mitigation requests. 818 o Added proposed operational requirement to support mitigation 819 efficacy reporting from DOTS clients. 821 o Added proposed operational requirement to cache lookups of all 822 kinds. 824 o Added proposed operational requirement regarding NAT traversal. 826 o Removed redundant mutual authentication requirement from data 827 channel requirements. 829 7.5. 00 revision 831 2015-10-15 833 7.6. Initial revision 835 2015-09-24 Andrew Mortensen 837 8. References 839 8.1. Normative References 841 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 842 DOI 10.17487/RFC0768, August 1980, 843 . 845 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 846 DOI 10.17487/RFC0791, September 1981, 847 . 849 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 850 RFC 793, DOI 10.17487/RFC0793, September 1981, 851 . 853 [RFC1035] Mockapetris, P., "Domain names - implementation and 854 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 855 November 1987, . 857 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 858 Communication Layers", STD 3, RFC 1122, 859 DOI 10.17487/RFC1122, October 1989, 860 . 862 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 863 DOI 10.17487/RFC1191, November 1990, 864 . 866 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 867 Requirement Levels", BCP 14, RFC 2119, 868 DOI 10.17487/RFC2119, March 1997, 869 . 871 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 872 Resource Identifier (URI): Generic Syntax", STD 66, 873 RFC 3986, DOI 10.17487/RFC3986, January 2005, 874 . 876 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 877 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 878 2006, . 880 [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing 881 (CIDR): The Internet Address Assignment and Aggregation 882 Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August 883 2006, . 885 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 886 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 887 . 889 [RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines 890 for Application Designers", RFC 5405, 891 DOI 10.17487/RFC5405, November 2008, 892 . 894 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 895 Address Text Representation", RFC 5952, 896 DOI 10.17487/RFC5952, August 2010, 897 . 899 8.2. Informative References 901 [I-D.ietf-dots-architecture] 902 Mortensen, A., Andreasen, F., Reddy, T., 903 christopher_gray3@cable.comcast.com, c., Compton, R., and 904 N. Teague, "Distributed-Denial-of-Service Open Threat 905 Signaling (DOTS) Architecture", draft-ietf-dots- 906 architecture-03 (work in progress), June 2017. 908 [I-D.ietf-dots-use-cases] 909 Dobbins, R., Fouant, S., Migault, D., Moskowitz, R., 910 Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS 911 Open Threat Signaling (DDoS) Open Threat Signaling", 912 draft-ietf-dots-use-cases-05 (work in progress), May 2017. 914 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 915 A., Peterson, J., Sparks, R., Handley, M., and E. 916 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 917 DOI 10.17487/RFC3261, June 2002, 918 . 920 [RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet 921 Denial-of-Service Considerations", RFC 4732, 922 DOI 10.17487/RFC4732, December 2006, 923 . 925 Authors' Addresses 927 Andrew Mortensen 928 Arbor Networks 929 2727 S. State St 930 Ann Arbor, MI 48104 931 United States 933 Email: amortensen@arbor.net 935 Robert Moskowitz 936 HTT Consulting 937 Oak Park, MI 42837 938 United States 940 Email: rgm@htt-consult.com 942 Tirumaleswar Reddy 943 McAfee, Inc. 944 Embassy Golf Link Business Park 945 Bangalore, Karnataka 560071 946 India 948 Email: TirumaleswarReddy_Konda@McAfee.com