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Mortensen 3 Internet-Draft Arbor Networks 4 Intended status: Informational R. Moskowitz 5 Expires: July 6, 2018 Huawei 6 T. Reddy 7 McAfee, Inc. 8 January 02, 2018 10 Distributed Denial of Service (DDoS) Open Threat Signaling Requirements 11 draft-ietf-dots-requirements-10 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 https://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 July 6, 2018. 36 Copyright Notice 38 Copyright (c) 2018 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 (https://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 . . . . . . . . . . . . . . . 8 59 2.3. Data Channel Requirements . . . . . . . . . . . . . . . . 12 60 2.4. Security Requirements . . . . . . . . . . . . . . . . . . 13 61 2.5. Data Model Requirements . . . . . . . . . . . . . . . . . 15 62 3. Congestion Control Considerations . . . . . . . . . . . . . . 16 63 3.1. Signal Channel . . . . . . . . . . . . . . . . . . . . . 16 64 3.2. Data Channel . . . . . . . . . . . . . . . . . . . . . . 16 65 4. Security Considerations . . . . . . . . . . . . . . . . . . . 16 66 5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 17 67 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 68 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 69 7.1. Normative References . . . . . . . . . . . . . . . . . . 17 70 7.2. Informative References . . . . . . . . . . . . . . . . . 19 71 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19 73 1. Introduction 75 1.1. Context and Motivation 77 Distributed Denial of Service (DDoS) attacks continue to plague 78 network operators around the globe, from Tier-1 service providers on 79 down to enterprises and small businesses. Attack scale and frequency 80 similarly have continued to increase, in part as a result of software 81 vulnerabilities leading to reflection and amplification attacks. 82 High-volume attacks saturating inbound links are now common, and the 83 impact of larger-scale attacks attract the attention of international 84 press agencies. 86 The greater impact of contemporary DDoS attacks has led to increased 87 focus on coordinated attack response. Many institutions and 88 enterprises lack the resources or expertise to operate on-premises 89 attack mitigation solutions themselves, or simply find themselves 90 constrained by local bandwidth limitations. To address such gaps, 91 security service providers have begun to offer on-demand traffic 92 scrubbing services, which aim to separate the DDoS traffic from 93 legitimate traffic and forward only the latter. Today each such 94 service offers a proprietary invocation interface for subscribers to 95 request attack mitigation, tying subscribers to proprietary signaling 96 implementations while also limiting the subset of network elements 97 capable of participating in the attack mitigation. As a result of 98 signaling interface incompatibility, attack responses may be 99 fragmentary or otherwise incomplete, leaving key players in the 100 attack path unable to assist in the defense. 102 The lack of a common method to coordinate a real-time response among 103 involved actors and network domains inhibits the speed and 104 effectiveness of DDoS attack mitigation. This document describes the 105 required characteristics of protocols enabling requests for DDoS 106 attack mitigation, reducing attack impact and leading to more 107 efficient defensive strategies. 109 DDoS Open Threat Signaling (DOTS) communicates the need for defensive 110 action in anticipation of or in response to an attack, but does not 111 dictate the form any defensive action takes. DOTS supplements calls 112 for help with pertinent details about the detected attack, allowing 113 entities participating in DOTS to form ad hoc, adaptive alliances 114 against DDoS attacks as described in the DOTS use cases 115 [I-D.ietf-dots-use-cases]. The requirements in this document are 116 derived from those use cases and [I-D.ietf-dots-architecture]. 118 1.2. Terminology 120 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 121 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 122 document are to be interpreted as described in [RFC2119]. 124 This document adopts the following terms: 126 DDoS: A distributed denial-of-service attack, in which traffic 127 originating from multiple sources are directed at a target on a 128 network. DDoS attacks are intended to cause a negative impact on 129 the availability of servers, services, applications, and/or other 130 functionality of an attack target. Denial-of-service 131 considerations are discussed in detail in [RFC4732]. 133 DDoS attack target: A network connected entity with a finite set of 134 resources, such as network bandwidth, memory or CPU, that is the 135 target of a DDoS attack. Potential targets include (but are not 136 limited to) network elements, network links, servers, and 137 services. 139 DDoS attack telemetry: Collected measurements and behavioral 140 characteristics defining the nature of a DDoS attack. 142 Countermeasure: An action or set of actions taken to recognize and 143 filter out DDoS attack traffic while passing legitimate traffic to 144 the attack target. 146 Mitigation: A set of countermeasures enforced against traffic 147 destined for the target or targets of a detected or reported DDoS 148 attack, where countermeasure enforcement is managed by an entity 149 in the network path between attack sources and the attack target. 150 Mitigation methodology is out of scope for this document. 152 Mitigator: An entity, typically a network element, capable of 153 performing mitigation of a detected or reported DDoS attack. For 154 the purposes of this document, this entity is a black box capable 155 of mitigation, making no assumptions about availability or design 156 of countermeasures, nor about the programmable interface(s) 157 between this entity and other network elements. The mitigator and 158 invoked DOTS server are assumed to belong to the same 159 administrative entity. 161 DOTS client: A DOTS-aware software module responsible for requesting 162 attack response coordination with other DOTS-aware elements. 164 DOTS server: A DOTS-aware software module handling and responding to 165 messages from DOTS clients. The DOTS server enables mitigation on 166 behalf of the DOTS client, if requested, by communicating the DOTS 167 client's request to the mitigator and returning selected mitigator 168 feedback to the requesting DOTS client. A DOTS server may also be 169 colocated with a mitigator. 171 DOTS agent: Any DOTS-aware software module capable of participating 172 in a DOTS signal or data channel. It can be a DOTS client, DOTS 173 server, or, as a logical agent, a DOTS gateway. 175 DOTS gateway: A DOTS-aware software module resulting from the 176 logical concatenation of a DOTS server and a DOTS client, 177 analogous to a Session Initiation Protocol (SIP) [RFC3261] Back- 178 to-Back User Agent (B2BUA) [RFC7092]. A DOTS gateway has a 179 client-facing side, which behaves as a DOTS server for downstream 180 clients, and a server-facing side, which performs the role of DOTS 181 client to upstream DOTS servers. Client-domain DOTS gateways are 182 DOTS gateways that are in the DOTS client's domain, while server- 183 domain DOTS gateways denote DOTS gateways that are in the DOTS 184 server's domain. DOTS gateways are described further in 185 [I-D.ietf-dots-architecture]. 187 Signal channel: A bidirectional, mutually authenticated 188 communication channel between two DOTS agents characterized by 189 resilience even in conditions leading to severe packet loss, such 190 as a volumetric DDoS attack causing network congestion. 192 DOTS signal: A concise authenticated status/control message 193 transmitted between DOTS agents, used to indicate the client's 194 need for mitigation, as well as to convey the status of any 195 requested mitigation. 197 Heartbeat: A message transmitted between DOTS agents over the signal 198 channel, used as a keep-alive and to measure peer health. 200 Data channel: A secure communication layer between two DOTS agents 201 used for infrequent bulk exchange of data not easily or 202 appropriately communicated through the signal channel under attack 203 conditions. 205 Filter: A specification of a matching network traffic flow or set of 206 flows. The filter will typically have a policy associated with 207 it, e.g., rate-limiting or discarding matching traffic [RFC4949]. 209 Blacklist: A filter list of addresses, prefixes, and/or other 210 identifiers indicating sources from which traffic should be 211 blocked, regardless of traffic content. 213 Whitelist: A list of addresses, prefixes, and/or other identifiers 214 indicating sources from which traffic should always be allowed, 215 regardless of contradictory data gleaned in a detected attack. 217 Multi-homed DOTS client: A DOTS client exchanging messages with 218 multiple DOTS servers, each in a separate administrative domain. 220 2. Requirements 222 This section describes the required features and characteristics of 223 the DOTS protocols. 225 The DOTS protocols enable and manage mitigation on behalf of a 226 network domain or resource which is or may become the focus of a DDoS 227 attack. An active DDoS attack against the entity controlling the 228 DOTS client need not be present before establishing a communication 229 channel between DOTS agents. Indeed, establishing a relationship 230 with peer DOTS agents during normal network conditions provides the 231 foundation for more rapid attack response against future attacks, as 232 all interactions setting up DOTS, including any business or service 233 level agreements, are already complete. Reachability information of 234 peer DOTS agents is provisioned to a DOTS client using a variety of 235 manual or dynamic methods. 237 The DOTS protocol must at a minimum make it possible for a DOTS 238 client to request a mitigator's aid mounting a defense, coordinated 239 by a DOTS server, against a suspected attack, signaling within or 240 between domains as requested by local operators. DOTS clients should 241 similarly be able to withdraw aid requests. DOTS requires no 242 justification from DOTS clients for requests for help, nor do DOTS 243 clients need to justify withdrawing help requests: the decision is 244 local to the DOTS clients' domain. Multi-homed DOTS clients must be 245 able to select the appropriate DOTS server(s) to which a mitigation 246 request is to be sent. Further multi-homing considerations are out 247 of scope. 249 Regular feedback between DOTS clients and DOTS servers supplement the 250 defensive alliance by maintaining a common understanding of the DOTS 251 agents' health and activity. Bidirectional communication between 252 DOTS clients and DOTS servers is therefore critical. 254 DOTS protocol implementations face competing operational goals when 255 maintaining this bidirectional communication stream. On the one 256 hand, the protocol must be resilient under extremely hostile network 257 conditions, providing continued contact between DOTS agents even as 258 attack traffic saturates the link. Such resiliency may be developed 259 several ways, but characteristics such as small message size, 260 asynchronous, redundant message delivery and minimal connection 261 overhead (when possible given local network policy) will tend to 262 contribute to the robustness demanded by a viable DOTS protocol. 263 Operators of peer DOTS-enabled domains may enable quality- or class- 264 of-service traffic tagging to increase the probability of successful 265 DOTS signal delivery, but DOTS does not require such policies be in 266 place. The DOTS solution indeed must be viable especially in their 267 absence. 269 On the other hand, DOTS must include protections ensuring message 270 confidentiality, integrity and authenticity to keep the protocol from 271 becoming another vector for the very attacks it's meant to help fight 272 off. DOTS clients must be able to authenticate DOTS servers, and 273 vice versa, to avoid exposing new attack surfaces when deploying 274 DOTS; specifically, to prevent DDoS mitigation in response to DOTS 275 signaling from becoming a new form of attack. In order to provide 276 this level of protection, DOTS agents must have a way to negotiate 277 and agree upon the terms of protocol security. Attacks against the 278 transport protocol should not offer a means of attack against the 279 message confidentiality, integrity and authenticity. 281 The DOTS server and client must also have some common method of 282 defining the scope of any mitigation performed by a mitigator, as 283 well as making adjustments to other commonly configurable features, 284 such as targeted port numbers, exchanging black- and white-lists, and 285 so on. 287 Finally, DOTS should be sufficiently extensible to meet future needs 288 in coordinated attack defense, although this consideration is 289 necessarily superseded by the other operational requirements. 291 2.1. General Requirements 293 GEN-001 Extensibility: Protocols and data models developed as part 294 of DOTS MUST be extensible in order to keep DOTS adaptable to 295 operational and proprietary DDoS defenses. Future extensions MUST 296 be backward compatible. DOTS protocols MUST use a version number 297 system to distinguish protocol revisions. Implementations of 298 older protocol versions SHOULD ignore information added to DOTS 299 messages as part of newer protocol versions. 301 GEN-002 Resilience and Robustness: The signaling protocol MUST be 302 designed to maximize the probability of signal delivery even under 303 the severely constrained network conditions imposed by particular 304 attack traffic. The protocol MUST be resilient, that is, continue 305 operating despite message loss and out-of-order or redundant 306 message delivery. In support of signaling protocol robustness, 307 DOTS signals SHOULD be conveyed over a transport not susceptible 308 to Head of Line Blocking. 310 GEN-003 Bidirectionality: To support peer health detection, to 311 maintain an open signal channel, and to increase the probability 312 of signal delivery during an attack, the signal channel MUST be 313 bidirectional, with client and server transmitting signals to each 314 other at regular intervals, regardless of any client request for 315 mitigation. Unidirectional messages MUST be supported within the 316 bidirectional signal channel to allow for unsolicited message 317 delivery, enabling asynchronous notifications between DOTS agents. 319 GEN-004 Bulk Data Exchange: Infrequent bulk data exchange between 320 DOTS agents can also significantly augment attack response 321 coordination, permitting such tasks as population of black- or 322 white-listed source addresses; address or prefix group aliasing; 323 exchange of incident reports; and other hinting or configuration 324 supplementing attack response. 326 As the resilience requirements for the DOTS signal channel mandate 327 small signal message size, a separate, secure data channel 328 utilizing a reliable transport protocol MUST be used for bulk data 329 exchange. 331 2.2. Signal Channel Requirements 333 SIG-001 Use of Common Transport Protocols: DOTS MUST operate over 334 common widely deployed and standardized transport protocols. 335 While connectionless transport such as the User Datagram Protocol 336 (UDP) [RFC0768] SHOULD be used for the signal channel, the 337 Transmission Control Protocol (TCP) [RFC0793] MAY be used if 338 necessary due to network policy or middlebox capabilities or 339 configurations. 341 SIG-002 Sub-MTU Message Size: To avoid message fragmentation and the 342 consequently decreased probability of message delivery over a 343 congested link, signaling protocol message size MUST be kept under 344 signaling Path Maximum Transmission Unit (PMTU), including the 345 byte overhead of any encapsulation, transport headers, and 346 transport- or message-level security. 348 DOTS agents SHOULD attempt to learn the PMTU through mechanisms 349 such as Path MTU Discovery [RFC1191] or Packetization Layer Path 350 MTU Discovery [RFC4821]. If the PMTU cannot be discovered, DOTS 351 agents SHOULD assume a PMTU of 1280 bytes. If IPv4 support on 352 legacy or otherwise unusual networks is a consideration and PMTU 353 is unknown, DOTS implementations MAY rely on a PMTU of 576 bytes, 354 as discussed in [RFC0791] and [RFC1122]. 356 SIG-003 Channel Health Monitoring: DOTS agents MUST support exchange 357 of heartbeat messages over the signal channel to monitor channel 358 health. Peer DOTS agents SHOULD regularly send heartbeats to each 359 other while a mitigation request is active. The heartbeat 360 interval during active mitigation is not specified, but SHOULD be 361 frequent enough to maintain any on-path NAT or Firewall bindings 362 during mitigation. 364 To support scenarios in which loss of heartbeat is used to trigger 365 mitigation, and to keep the channel active, DOTS clients MAY 366 solicit heartbeat exchanges after successful mutual 367 authentication. When DOTS agents are exchanging heartbeats and no 368 mitigation request is active, either agent MAY request changes to 369 the heartbeat rate. For example, a DOTS server might want to 370 reduce heartbeat frequency or cease heartbeat exchanges when an 371 active DOTS client has not requested mitigation, in order to 372 control load. 374 Following mutual authentication, a signal channel MUST be 375 considered active until a DOTS agent explicitly ends the session, 376 or either DOTS agent fails to receive heartbeats from the other 377 after a mutually agreed upon retransmission procedure has been 378 exhausted. Because heartbeat loss is much more likely during 379 volumetric attack, DOTS agents SHOULD avoid signal channel 380 termination when mitigation is active and heartbeats are not 381 received by either DOTS agent for an extended period. In such 382 circumstances, DOTS clients MAY attempt to reestablish the signal 383 channel, but SHOULD continue to send heartbeats so that the DOTS 384 server knows the session is still alive. DOTS servers SHOULD 385 monitor the attack, using feedback from the mitigator and other 386 available sources, and MAY use the absence of attack traffic and 387 lack of client heartbeats as an indication the signal channel is 388 defunct. 390 SIG-004 Channel Redirection: In order to increase DOTS operational 391 flexibility and scalability, DOTS servers SHOULD be able to 392 redirect DOTS clients to another DOTS server at any time. DOTS 393 clients MUST NOT assume the redirection target DOTS server shares 394 security state with the redirecting DOTS server. DOTS clients MAY 395 attempt abbreviated security negotiation methods supported by the 396 protocol, such as DTLS session resumption, but MUST be prepared to 397 negotiate new security state with the redirection target DOTS 398 server. 400 Due to the increased likelihood of packet loss caused by link 401 congestion during an attack, DOTS servers SHOULD NOT redirect 402 while mitigation is enabled during an active attack against a 403 target in the DOTS client's domain. 405 SIG-005 Mitigation Requests and Status: Authorized DOTS clients MUST 406 be able to request scoped mitigation from DOTS servers. DOTS 407 servers MUST send mitigation request status in response to granted 408 DOTS clients requests for mitigation. If a DOTS server rejects an 409 authorized request for mitigation, the DOTS server MUST include a 410 reason for the rejection in the status message sent to the client. 412 Due to the higher likelihood of packet loss during a DDoS attack, 413 DOTS servers SHOULD regularly send mitigation status to authorized 414 DOTS clients which have requested and been granted mitigation, 415 regardless of client requests for mitigation status. 417 When DOTS client-requested mitigation is active, DOTS server 418 status messages SHOULD include the following mitigation metrics: 420 * Total number of packets blocked by the mitigation 422 * Current number of packets per second blocked 424 * Total number of bytes blocked 426 * Current number of bytes per second blocked 427 DOTS clients MAY take these metrics into account when determining 428 whether to ask the DOTS server to cease mitigation. 430 A DOTS client MAY withdraw a mitigation request at any time, 431 regardless of whether mitigation is currently active. The DOTS 432 server MUST immediately acknowledge a DOTS client's request to 433 stop mitigation. 435 To protect against route or DNS flapping caused by a client 436 rapidly toggling mitigation, and to dampen the effect of 437 oscillating attacks, DOTS servers MAY allow mitigation to continue 438 for a limited period after acknowledging a DOTS client's 439 withdrawal of a mitigation request. During this period, DOTS 440 server status messages SHOULD indicate that mitigation is active 441 but terminating. 443 The initial active-but-terminating period is implementation- and 444 deployment- specific, but SHOULD be sufficiently long to absorb 445 latency incurred by route propagation. If the client requests 446 mitigation again before the initial active-but-terminating period 447 elapses, the DOTS server MAY exponentially increase the active- 448 but-terminating period up to a maximum of 300 seconds (5 minutes). 449 After the active-but-terminating period elapses, the DOTS server 450 MUST treat the mitigation as terminated, as the DOTS client is no 451 longer responsible for the mitigation. For example, if there is a 452 financial relationship between the DOTS client and server domains, 453 the DOTS client ceases incurring cost at this point. 455 SIG-006 Mitigation Lifetime: DOTS servers MUST support mitigation 456 lifetimes, and MUST terminate a mitigation when the lifetime 457 elapses. DOTS servers also MUST support renewal of mitigation 458 lifetimes in mitigation requests from DOTS clients, allowing 459 clients to extend mitigation as necessary for the duration of an 460 attack. 462 DOTS servers MUST treat a mitigation terminated due to lifetime 463 expiration exactly as if the DOTS client originating the 464 mitigation had asked to end the mitigation, including the active- 465 but-terminating period, as described above in SIG-005. 467 DOTS clients MUST include a mitigation lifetime in all mitigation 468 requests. 470 DOTS servers SHOULD support indefinite mitigation lifetimes, 471 enabling architectures in which the mitigator is always in the 472 traffic path to the resources for which the DOTS client is 473 requesting protection. DOTS clients MUST be prepared to not be 474 granted mitigations with indefinite lifetimes. DOTS servers MAY 475 refuse mitigations with indefinite lifetimes, for policy reasons. 476 The reasons themselves are out of scope. If the DOTS server does 477 not grant a mitigation request with an indefinite mitigation 478 lifetime, it MUST set the lifetime to a value that is configured 479 locally. That value MUST be returned in a reply to the requesting 480 DOTS client. 482 SIG-007 Mitigation Scope: DOTS clients MUST indicate desired 483 mitigation scope. The scope type will vary depending on the 484 resources requiring mitigation. All DOTS agent implementations 485 MUST support the following required scope types: 487 * IPv4 prefixes in CIDR notation [RFC4632] 489 * IPv6 prefixes [RFC4291][RFC5952] 491 * Domain names [RFC1035] 493 The following mitigation scope types are OPTIONAL: 495 * Uniform Resource Identifiers [RFC3986] 497 DOTS servers MUST be able to resolve domain names and (when 498 supported) URIs. How name resolution is managed on the DOTS 499 server is implementation-specific. 501 DOTS agents MUST support mitigation scope aliases, allowing DOTS 502 clients and servers to refer to collections of protected resources 503 by an opaque identifier created through the data channel, direct 504 configuration, or other means. Domain name and URI mitigation 505 scopes may be thought of as a form of scope alias, in which the 506 addresses to which the domain name or URI resolve represent the 507 full scope of the mitigation. 509 If there is additional information available narrowing the scope 510 of any requested attack response, such as targeted port range, 511 protocol, or service, DOTS clients SHOULD include that information 512 in client mitigation requests. DOTS clients MAY also include 513 additional attack details. DOTS servers MAY ignore such 514 supplemental information when enabling countermeasures on the 515 mitigator. 517 As an active attack evolves, DOTS clients MUST be able to adjust 518 as necessary the scope of requested mitigation by refining the 519 scope of resources requiring mitigation. 521 A DOTS client may obtain the mitigation scope through direct 522 provisioning or through implementation-specific methods of 523 discovery. DOTS clients MUST support at least one mechanism to 524 obtain mitigation scope. 526 SIG-008 Mitigation Efficacy: When a mitigation request is active, 527 DOTS clients SHOULD transmit a metric of perceived mitigation 528 efficacy to the DOTS server. DOTS servers MAY use the efficacy 529 metric to adjust countermeasures activated on a mitigator on 530 behalf of a DOTS client. 532 SIG-009 Conflict Detection and Notification: Multiple DOTS clients 533 controlled by a single administrative entity may send conflicting 534 mitigation requests for pools of protected resources as a result 535 of misconfiguration, operator error, or compromised DOTS clients. 536 DOTS servers in the same administrative domain attempting to honor 537 conflicting requests may flap network route or DNS information, 538 degrading the networks attempting to participate in attack 539 response with the DOTS clients. DOTS servers in a single 540 administrative domain SHALL detect such conflicting requests, and 541 SHALL notify the DOTS clients in conflict. The notification 542 SHOULD indicate the nature and scope of the conflict, for example, 543 the overlapping prefix range in a conflicting mitigation request. 545 SIG-010: Network Address Translator Traversal: DOTS clients may be 546 deployed behind a Network Address Translator (NAT), and need to 547 communicate with DOTS servers through the NAT. DOTS protocols 548 MUST therefore be capable of traversing NATs. 550 If UDP is used as the transport for the DOTS signal channel, all 551 considerations in "Middlebox Traversal Guidelines" in [RFC8085] 552 apply to DOTS. Regardless of transport, DOTS protocols MUST 553 follow established best common practices (BCPs) for NAT traversal. 555 2.3. Data Channel Requirements 557 The data channel is intended to be used for bulk data exchanges 558 between DOTS agents. Unlike the signal channel, which must operate 559 nominally even when confronted with signal degradation due to 560 significant packet loss, the data channel is not expected to be 561 constructed to deal with attack conditions. As the primary function 562 of the data channel is data exchange, a reliable transport is 563 required in order for DOTS agents to detect data delivery success or 564 failure. 566 The DOTS data channel protocol MUST be extensible. We anticipate the 567 data channel will be used for such purposes as configuration or 568 resource discovery. For example, a DOTS client may submit to a DOTS 569 server a collection of prefixes it wants to refer to by alias when 570 requesting mitigation, to which the server would respond with a 571 success status and the new prefix group alias, or an error status and 572 message in the event the DOTS client's data channel request failed. 573 The transactional nature of such data exchanges suggests a separate 574 set of requirements for the data channel, while the potentially 575 sensitive content sent between DOTS agents requires extra precautions 576 to ensure data privacy and authenticity. 578 DATA-001 Reliable transport: Messages sent over the data channel 579 MUST be delivered reliably, in order sent. 581 DATA-002 Data privacy and integrity: Transmissions over the data 582 channel are likely to contain operationally or privacy-sensitive 583 information or instructions from the remote DOTS agent. Theft or 584 modification of data channel transmissions could lead to 585 information leaks or malicious transactions on behalf of the 586 sending agent (see Section 4 below). Consequently data sent over 587 the data channel MUST be encrypted and authenticated using current 588 industry best practices. DOTS servers MUST enable means to 589 prevent leaking operationally or privacy-sensitive data. Although 590 administrative entities participating in DOTS may detail what data 591 may be revealed to third-party DOTS agents, such considerations 592 are not in scope for this document. 594 DATA-003 Resource Configuration: To help meet the general and signal 595 channel requirements in Section 2.2, DOTS server implementations 596 MUST provide an interface to configure resource identifiers, as 597 described in SIG-007. DOTS server implementations MAY expose 598 additional configurability. Additional configurability is 599 implementation-specific. 601 DATA-004 Black- and whitelist management: DOTS servers MUST provide 602 methods for DOTS clients to manage black- and white-lists of 603 traffic destined for resources belonging to a client. 605 For example, a DOTS client should be able to create a black- or 606 whitelist entry, retrieve a list of current entries from either 607 list, update the content of either list, and delete entries as 608 necessary. 610 How a DOTS server authorizes DOTS client management of black- and 611 white-list entries is implementation-specific. 613 2.4. Security Requirements 615 DOTS must operate within a particularly strict security context, as 616 an insufficiently protected signal or data channel may be subject to 617 abuse, enabling or supplementing the very attacks DOTS purports to 618 mitigate. 620 SEC-001 Peer Mutual Authentication: DOTS agents MUST authenticate 621 each other before a DOTS signal or data channel is considered 622 valid. The method of authentication is not specified, but should 623 follow current industry best practices with respect to any 624 cryptographic mechanisms to authenticate the remote peer. 626 SEC-002 Message Confidentiality, Integrity and Authenticity: DOTS 627 protocols MUST take steps to protect the confidentiality, 628 integrity and authenticity of messages sent between client and 629 server. While specific transport- and message-level security 630 options are not specified, the protocols MUST follow current 631 industry best practices for encryption and message authentication. 633 In order for DOTS protocols to remain secure despite advancements 634 in cryptanalysis and traffic analysis, DOTS agents MUST be able to 635 negotiate the terms and mechanisms of protocol security, subject 636 to the interoperability and signal message size requirements 637 above. 639 While the interfaces between downstream DOTS server and upstream 640 DOTS client within a DOTS gateway are implementation-specific, 641 those interfaces nevertheless MUST provide security equivalent to 642 that of the signal channels bridged by gateways in the signaling 643 path. For example, when a DOTS gateway consisting of a DOTS 644 server and DOTS client is running on the same logical device, the 645 two DOTS agents could be implemented within the same process 646 security boundary. 648 SEC-003 Message Replay Protection: To prevent a passive attacker 649 from capturing and replaying old messages, and thereby potentially 650 disrupting or influencing the network policy of the receiving DOTS 651 agent's domain, DOTS protocols MUST provide a method for replay 652 detection and prevention. 654 Within the signal channel, messages MUST be uniquely identified 655 such that replayed or duplicated messages can be detected and 656 discarded. Unique mitigation requests MUST be processed at most 657 once. 659 SEC-004 Authorization: DOTS servers MUST authorize all messages from 660 DOTS clients which pertain to mitigation, configuration, 661 filtering, or status. 663 DOTS servers MUST reject mitigation requests with scopes which the 664 DOTS client is not authorized to manage. 666 Likewise, DOTS servers MUST refuse to allow creation, modification 667 or deletion of scope aliases and black-/white-lists when the DOTS 668 client is unauthorized. 670 The modes of authorization are implementation-specific. 672 2.5. Data Model Requirements 674 The value of DOTS is in standardizing a mechanism to permit elements, 675 networks or domains under threat of DDoS attack to request aid 676 mitigating the effects of any such attack. A well-structured DOTS 677 data model is therefore critical to the development of successful 678 DOTS protocols. 680 DM-001: Structure: The data model structure for the DOTS protocol 681 may be described by a single module, or be divided into related 682 collections of hierarchical modules and sub-modules. If the data 683 model structure is split across modules, those distinct modules 684 MUST allow references to describe the overall data model's 685 structural dependencies. 687 DM-002: Versioning: To ensure interoperability between DOTS protocol 688 implementations, data models MUST be versioned. How the protocols 689 represent data model versions is not defined in this document. 691 DM-003: Mitigation Status Representation: The data model MUST 692 provide the ability to represent a request for mitigation and the 693 withdrawal of such a request. The data model MUST also support a 694 representation of currently requested mitigation status, including 695 failures and their causes. 697 DM-004: Mitigation Scope Representation: The data model MUST support 698 representation of a requested mitigation's scope. As mitigation 699 scope may be represented in several different ways, per SIG-007 700 above, the data model MUST be capable of flexible representation 701 of mitigation scope. 703 DM-005: Mitigation Lifetime Representation: The data model MUST 704 support representation of a mitigation request's lifetime, 705 including mitigations with no specified end time. 707 DM-006: Mitigation Efficacy Representation: The data model MUST 708 support representation of a DOTS client's understanding of the 709 efficacy of a mitigation enabled through a mitigation request. 711 DM-007: Acceptable Signal Loss Representation: The data model MUST 712 be able to represent the DOTS agent's preference for acceptable 713 signal loss when establishing a signal channel, as described in 714 GEN-002. 716 DM-008: Heartbeat Interval Representation: The data model MUST be 717 able to represent the DOTS agent's preferred heartbeat interval, 718 which the client may include when establishing the signal channel, 719 as described in SIG-003. 721 DM-009: Relationship to Transport: The DOTS data model MUST NOT 722 depend on the specifics of any transport to represent fields in 723 the model. 725 3. Congestion Control Considerations 727 3.1. Signal Channel 729 As part of a protocol expected to operate over links affected by DDoS 730 attack traffic, the DOTS signal channel MUST NOT contribute 731 significantly to link congestion. To meet the signal channel 732 requirements above, DOTS signal channel implementations SHOULD 733 support connectionless transports. However, some connectionless 734 transports when deployed naively can be a source of network 735 congestion, as discussed in [RFC5405]. Signal channel 736 implementations using such connectionless transports, such as UDP, 737 therefore MUST include a congestion control mechanism. 739 Signal channel implementations using TCP may rely on built-in TCP 740 congestion control support. 742 3.2. Data Channel 744 As specified in DATA-001, the data channel requires reliable, in- 745 order message delivery. Data channel implementations using TCP may 746 rely on the TCP implementation's built-in congestion control 747 mechanisms. 749 4. Security Considerations 751 DOTS is at risk from three primary attacks: 753 o DOTS agent impersonation 755 o Traffic injection 757 o Signaling blocking 759 The DOTS protocol MUST be designed for minimal data transfer to 760 address the blocking risk. Impersonation and traffic injection 761 mitigation can be managed through current secure communications best 762 practices. See Section 2.4 above for a detailed discussion. 764 5. Contributors 766 Mohamed Boucadair 767 Orange 769 mohamed.boucadair@orange.com 771 Flemming Andreasen 772 Cisco Systems, Inc. 774 fandreas@cisco.com 776 Dave Dolson 777 Sandvine 779 ddolson@sandvine.com 781 6. Acknowledgments 783 Thanks to Roman Danyliw and Matt Richardson for careful reading and 784 feedback. 786 7. References 788 7.1. Normative References 790 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 791 DOI 10.17487/RFC0768, August 1980, 792 . 794 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 795 DOI 10.17487/RFC0791, September 1981, 796 . 798 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 799 RFC 793, DOI 10.17487/RFC0793, September 1981, 800 . 802 [RFC1035] Mockapetris, P., "Domain names - implementation and 803 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 804 November 1987, . 806 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 807 Communication Layers", STD 3, RFC 1122, 808 DOI 10.17487/RFC1122, October 1989, 809 . 811 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 812 DOI 10.17487/RFC1191, November 1990, 813 . 815 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 816 Requirement Levels", BCP 14, RFC 2119, 817 DOI 10.17487/RFC2119, March 1997, 818 . 820 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 821 Resource Identifier (URI): Generic Syntax", STD 66, 822 RFC 3986, DOI 10.17487/RFC3986, January 2005, 823 . 825 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 826 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 827 2006, . 829 [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing 830 (CIDR): The Internet Address Assignment and Aggregation 831 Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August 832 2006, . 834 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 835 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 836 . 838 [RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines 839 for Application Designers", RFC 5405, 840 DOI 10.17487/RFC5405, November 2008, 841 . 843 [RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage 844 Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, 845 March 2017, . 847 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 848 Address Text Representation", RFC 5952, 849 DOI 10.17487/RFC5952, August 2010, 850 . 852 7.2. Informative References 854 [I-D.ietf-dots-architecture] 855 Mortensen, A., Andreasen, F., Reddy, T., 856 christopher_gray3@cable.comcast.com, c., Compton, R., and 857 N. Teague, "Distributed-Denial-of-Service Open Threat 858 Signaling (DOTS) Architecture", draft-ietf-dots- 859 architecture-05 (work in progress), October 2017. 861 [I-D.ietf-dots-use-cases] 862 Dobbins, R., Migault, D., Fouant, S., Moskowitz, R., 863 Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS 864 Open Threat Signaling", draft-ietf-dots-use-cases-09 (work 865 in progress), November 2017. 867 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 868 A., Peterson, J., Sparks, R., Handley, M., and E. 869 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 870 DOI 10.17487/RFC3261, June 2002, 871 . 873 [RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session 874 Initiation Protocol (SIP) Back-to-Back User Agents", 875 RFC 7092, DOI 10.17487/RFC7092, December 2013, 876 . 878 [RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet 879 Denial-of-Service Considerations", RFC 4732, 880 DOI 10.17487/RFC4732, December 2006, 881 . 883 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", 884 FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, 885 . 887 Authors' Addresses 889 Andrew Mortensen 890 Arbor Networks 891 2727 S. State St 892 Ann Arbor, MI 48104 893 United States 895 Email: amortensen@arbor.net 896 Robert Moskowitz 897 Huawei 898 Oak Park, MI 42837 899 United States 901 Email: rgm@htt-consult.com 903 Tirumaleswar Reddy 904 McAfee, Inc. 905 Embassy Golf Link Business Park 906 Bangalore, Karnataka 560071 907 India 909 Email: TirumaleswarReddy_Konda@McAfee.com