idnits 2.17.1 draft-ietf-dots-requirements-09.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- ** The document seems to lack an IANA Considerations section. (See Section 2.2 of https://www.ietf.org/id-info/checklist for how to handle the case when there are no actions for IANA.) Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (December 19, 2017) is 2320 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 793 (Obsoleted by RFC 9293) ** Obsolete normative reference: RFC 5405 (Obsoleted by RFC 8085) == Outdated reference: A later version (-18) exists of draft-ietf-dots-architecture-05 == Outdated reference: A later version (-25) exists of draft-ietf-dots-use-cases-09 Summary: 3 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DOTS A. Mortensen 3 Internet-Draft Arbor Networks 4 Intended status: Informational R. Moskowitz 5 Expires: June 22, 2018 Huawei 6 T. Reddy 7 McAfee, Inc. 8 December 19, 2017 10 Distributed Denial of Service (DDoS) Open Threat Signaling Requirements 11 draft-ietf-dots-requirements-09 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 June 22, 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 (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 . . . . . . . . . . . . . . . . . 18 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 Once-staggering attack traffic volume is now the norm, and the impact 83 of larger-scale attacks attract the attention of international press 84 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 focus of a DDoS attack. Potential targets include (but 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]. Client-side DOTS gateways 179 are DOTS gateways that are in the DOTS client's domain, while 180 server-side DOTS gateways denote DOTS gateways that are in the 181 DOTS server's domain. DOTS gateways are discussed in detail in 182 [I-D.ietf-dots-architecture]. 184 Signal channel: A bidirectional, mutually authenticated 185 communication channel between two 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 Data channel: A secure communication layer between two DOTS agents 198 used for infrequent bulk exchange of data not easily or 199 appropriately communicated through the signal channel under attack 200 conditions. 202 Filter: A specification of a matching network traffic flow or set of 203 flows. The filter will typically have a policy associated with 204 it, e.g., rate-limiting or discarding matching traffic [RFC4949]. 206 Blacklist: A filter list of addresses, prefixes, and/or other 207 identifiers indicating sources from which traffic should be 208 blocked, regardless of traffic content. 210 Whitelist: A list of addresses, prefixes, and/or other identifiers 211 indicating sources from which traffic should always be allowed, 212 regardless of contradictory data gleaned in a detected attack. 214 Multi-homed DOTS client: A DOTS client exchanging messages with 215 multiple DOTS servers, each in a separate administrative domain. 217 2. Requirements 219 This section describes the required features and characteristics of 220 the DOTS protocols. 222 The DOTS protocols enable and manage mitigation on behalf of a 223 network domain or resource which is or may become the focus of a DDoS 224 attack. An active DDoS attack against the entity controlling the 225 DOTS client need not be present before establishing a communication 226 channel between DOTS agents. Indeed, establishing a relationship 227 with peer DOTS agents during normal network conditions provides the 228 foundation for more rapid attack response against future attacks, as 229 all interactions setting up DOTS, including any business or service 230 level agreements, are already complete. Reachability information of 231 peer DOTS agents is provisioned to a DOTS client using a variety of 232 manual or dynamic methods. 234 The DOTS protocol must at a minimum make it possible for a DOTS 235 client to request a mitigator's aid mounting a defense, coordinated 236 by a DOTS server, against a suspected attack, signaling within or 237 between domains as requested by local operators. DOTS clients should 238 similarly be able to withdraw aid requests. DOTS requires no 239 justification from DOTS clients for requests for help, nor do DOTS 240 clients need to justify withdrawing help requests: the decision is 241 local to the DOTS clients' domain. Multi-homed DOTS clients must be 242 able to select the appropriate DOTS server(s) to which a mitigation 243 request is to be sent. Further multi-homing considerations are out 244 of scope. 246 Regular feedback between DOTS clients and DOTS servers supplement the 247 defensive alliance by maintaining a common understanding of the DOTS 248 agents' health and activity. Bidirectional communication between 249 DOTS clients and DOTS servers is therefore critical. 251 DOTS protocol implementations face competing operational goals when 252 maintaining this bidirectional communication stream. On the one 253 hand, the protocol must be resilient under extremely hostile network 254 conditions, providing continued contact between DOTS agents even as 255 attack traffic saturates the link. Such resiliency may be developed 256 several ways, but characteristics such as small message size, 257 asynchronous, redundant message delivery and minimal connection 258 overhead (when possible given local network policy) will tend to 259 contribute to the robustness demanded by a viable DOTS protocol. 260 Operators of peer DOTS-enabled domains may enable quality- or class- 261 of-service traffic tagging to increase the probability of successful 262 DOTS signal delivery, but DOTS does not require such policies be in 263 place. The DOTS solution indeed must be viable especially in their 264 absence. 266 On the other hand, DOTS must include protections ensuring message 267 confidentiality, integrity and authenticity to keep the protocol from 268 becoming another vector for the very attacks it's meant to help fight 269 off. DOTS clients must be able to authenticate DOTS servers, and 270 vice versa, to avoid exposing new attack surfaces when deploying 271 DOTS; specifically, to prevent DDoS mitigation in response to DOTS 272 signaling from becoming a new form of attack. In order to provide 273 this level of protection, DOTS agents must have a way to negotiate 274 and agree upon the terms of protocol security. Attacks against the 275 transport protocol should not offer a means of attack against the 276 message confidentiality, integrity and authenticity. 278 The DOTS server and client must also have some common method of 279 defining the scope of any mitigation performed by a mitigator, as 280 well as making adjustments to other commonly configurable features, 281 such as listen port numbers, exchanging black- and white-lists, and 282 so on. 284 Finally, DOTS should be sufficiently extensible to meet future needs 285 in coordinated attack defense, although this consideration is 286 necessarily superseded by the other operational requirements. 288 2.1. General Requirements 290 GEN-001 Extensibility: Protocols and data models developed as part 291 of DOTS MUST be extensible in order to keep DOTS adaptable to 292 operational and proprietary DDoS defenses. Future extensions MUST 293 be backward compatible. DOTS protocols MUST use a version number 294 system to distinguish protocol revisions. Implementations of 295 older protocol versions SHOULD ignore information added to DOTS 296 messages as part of newer protocol versions. 298 GEN-002 Resilience and Robustness: The signaling protocol MUST be 299 designed to maximize the probability of signal delivery even under 300 the severely constrained network conditions imposed by particular 301 attack traffic. The protocol MUST be resilient, that is, continue 302 operating despite message loss and out-of-order or redundant 303 message delivery. In support of signaling protocol robustness, 304 DOTS signals SHOULD be conveyed over a transport not susceptible 305 to Head of Line Blocking. 307 GEN-003 Bidirectionality: To support peer health detection, to 308 maintain an open signal channel, and to increase the probability 309 of signal delivery during attack, the signal channel MUST be 310 bidirectional, with client and server transmitting signals to each 311 other at regular intervals, regardless of any client request for 312 mitigation. Unidirectional messages MUST be supported within the 313 bidirectional signal channel to allow for unsolicited message 314 delivery, enabling asynchronous notifications between DOTS agents. 316 GEN-004 Bulk Data Exchange: Infrequent bulk data exchange between 317 DOTS agents can also significantly augment attack response 318 coordination, permitting such tasks as population of black- or 319 white-listed source addresses; address or prefix group aliasing; 320 exchange of incident reports; and other hinting or configuration 321 supplementing attack response. 323 As the resilience requirements for the DOTS signal channel mandate 324 small signal message size, a separate, secure data channel 325 utilizing a reliable transport protocol MUST be used for bulk data 326 exchange. 328 2.2. Signal Channel Requirements 330 SIG-001 Use of Common Transport Protocols: DOTS MUST operate over 331 common widely deployed and standardized transport protocols. 332 While connectionless transport such as the User Datagram Protocol 333 (UDP) [RFC0768] SHOULD be used for the signal channel, the 334 Transmission Control Protocol (TCP) [RFC0793] MAY be used if 335 necessary due to network policy or middlebox capabilities or 336 configurations. 338 SIG-002 Sub-MTU Message Size: To avoid message fragmentation and the 339 consequently decreased probability of message delivery over a 340 congested link, signaling protocol message size MUST be kept under 341 signaling Path Maximum Transmission Unit (PMTU), including the 342 byte overhead of any encapsulation, transport headers, and 343 transport- or message-level security. 345 DOTS agents SHOULD attempt to learn the PMTU through mechanisms 346 such as Path MTU Discovery [RFC1191] or Packetization Layer Path 347 MTU Discovery [RFC4821]. If the PMTU cannot be discovered, DOTS 348 agents SHOULD assume a PMTU of 1280 bytes. If IPv4 support on 349 legacy or otherwise unusual networks is a consideration and PMTU 350 is unknown, DOTS implementations MAY rely on a PMTU of 576 bytes, 351 as discussed in [RFC0791] and [RFC1122]. 353 SIG-003 Channel Health Monitoring: DOTS agents MUST support exchange 354 of heartbeat messages over the signal channel to monitor channel 355 health. Peer DOTS agents SHOULD regularly send heartbeats to each 356 other while a mitigation request is active. The heartbeat 357 interval during active mitigation is not specified, but SHOULD be 358 frequent enough to maintain any on-path NAT bindings during 359 mitigation. 361 To support scenarios in which loss of heartbeat is used to trigger 362 mitigation, and to keep the channel active, DOTS clients MAY 363 solicit heartbeat exchanges after successful mutual 364 authentication. When DOTS agents are exchanging heartbeats and no 365 mitigation request is active, either agent MAY request changes to 366 the heartbeat rate. For example, a DOTS server might want to 367 reduce heartbeat frequency or cease heartbeat exchanges when an 368 active DOTS client has not requested mitigation, in order to 369 control load. 371 Following mutual authentication, a signal channel MUST be 372 considered active until a DOTS agent explicitly ends the session, 373 or either DOTS agent fails to receive heartbeats from the other 374 after a mutually agreed upon retransmission procedure has been 375 exhausted. Because heartbeat loss is much more likely during 376 volumetric attack, DOTS agents SHOULD avoid signal channel 377 termination when mitigation is active and heartbeats are not 378 received by either DOTS agent for an extended period. In such 379 circumstances, DOTS clients MAY attempt to reestablish the signal 380 channel, but SHOULD continue to send heartbeats so that the DOTS 381 server knows the session is still partially alive. DOTS servers 382 SHOULD monitor the attack, using feedback from the mitigator and 383 other available sources, and MAY use the absence of attack traffic 384 and lack of client heartbeats as an indication the signal channel 385 is defunct. 387 SIG-004 Channel Redirection: In order to increase DOTS operational 388 flexibility and scalability, DOTS servers SHOULD be able to 389 redirect DOTS clients to another DOTS server at any time. DOTS 390 clients MUST NOT assume the redirection target DOTS server shares 391 security state with the redirecting DOTS server. DOTS clients MAY 392 attempt abbreviated security negotiation methods supported by the 393 protocol, such as DTLS session resumption, but MUST be prepared to 394 negotiate new security state with the redirection target DOTS 395 server. 397 Due to the increased likelihood of packet loss caused by link 398 congestion during an attack, DOTS servers SHOULD NOT redirect 399 while mitigation is enabled during an active attack against a 400 target in the DOTS client's domain. 402 SIG-005 Mitigation Requests and Status: Authorized DOTS clients MUST 403 be able to request scoped mitigation from DOTS servers. DOTS 404 servers MUST send mitigation request status in response to granted 405 DOTS clients requests for mitigation. If a DOTS server rejects an 406 authorized request for mitigation, the DOTS server MUST include a 407 reason for the rejection in the status message sent to the client. 409 Due to the higher likelihood of packet loss during a DDoS attack, 410 DOTS servers SHOULD regularly send mitigation status to authorized 411 DOTS clients which have requested and been granted mitigation, 412 regardless of client requests for mitigation status. 414 When DOTS client-requested mitigation is active, DOTS server 415 status messages SHOULD include the following mitigation metrics: 417 * Total number of packets blocked by the mitigation 419 * Current number of packets per second blocked 421 * Total number of bytes blocked 423 * Current number of bytes per second blocked 424 DOTS clients MAY take these metrics into account when determining 425 whether to ask the DOTS server to cease mitigation. 427 A DOTS client MAY withdraw a mitigation request at any time, 428 regardless of whether mitigation is currently active. The DOTS 429 server MUST immediately acknowledge a DOTS client's request to 430 stop mitigation. 432 To protect against route or DNS flapping caused by a client 433 rapidly toggling mitigation, and to dampen the effect of 434 oscillating attacks, DOTS servers MAY allow mitigation to continue 435 for a limited period after acknowledging a DOTS client's 436 withdrawal of a mitigation request. During this period, DOTS 437 server status messages SHOULD indicate that mitigation is active 438 but terminating. 440 The initial active-but-terminating period is implementation- and 441 deployment- specific, but SHOULD be sufficiently long to absorb 442 latency incurred by route propagation. If the client requests 443 mitigation again before the initial active-but-terminating period 444 elapses, the DOTS server MAY exponentially increase the active- 445 but-terminating period up to a maximum of 300 seconds (5 minutes). 446 After the active-but-terminating period elapses, the DOTS server 447 MUST treat the mitigation as terminated, as the DOTS client is no 448 longer responsible for the mitigation. For example, if there is a 449 financial relationship between the DOTS client and server domains, 450 the DOTS client ceases incurring cost at this point. 452 SIG-006 Mitigation Lifetime: DOTS servers MUST support mitigation 453 lifetimes, and MUST terminate a mitigation when the lifetime 454 elapses. DOTS servers also MUST support renewal of mitigation 455 lifetimes in mitigation requests from DOTS clients, allowing 456 clients to extend mitigation as necessary for the duration of an 457 attack. 459 DOTS servers MUST treat a mitigation terminated due to lifetime 460 expiration exactly as if the DOTS client originating the 461 mitigation had asked to end the mitigation, including the active- 462 but-terminating period, as described above in SIG-005. 464 DOTS clients MUST include a mitigation lifetime in all mitigation 465 requests. 467 DOTS servers SHOULD support indefinite mitigation lifetimes, 468 enabling architectures in which the mitigator is always in the 469 traffic path to the resources for which the DOTS client is 470 requesting protection. DOTS clients MUST be prepared to not be 471 granted mitigations with indefinite lifetimes. DOTS servers MAY 472 refuse mitigations with indefinite lifetimes, for policy reasons. 473 The reasons themselves are out of scope. If the DOTS server does 474 not grant a mitigation request with an indefinite mitigation 475 lifetime, it MUST set the lifetime to a value that is configured 476 locally. That value MUST be returned in a reply to the requesting 477 DOTS client. 479 SIG-007 Mitigation Scope: DOTS clients MUST indicate desired 480 mitigation scope. The scope type will vary depending on the 481 resources requiring mitigation. All DOTS agent implementations 482 MUST support the following required scope types: 484 * IPv4 prefixes in CIDR notation [RFC4632] 486 * IPv6 prefixes [RFC4291][RFC5952] 488 * Domain names [RFC1035] 490 The following mitigation scope types are OPTIONAL: 492 * Uniform Resource Identifiers [RFC3986] 494 DOTS servers MUST be able to resolve domain names and URIs. How 495 name resolution is managed on the DOTS server is implementation- 496 specific. 498 DOTS agents MUST support mitigation scope aliases, allowing DOTS 499 clients and servers to refer to collections of protected resources 500 by an opaque identifier created through the data channel, direct 501 configuration, or other means. Domain name and URI mitigation 502 scopes may be thought of as a form of scope alias, in which the 503 addresses to which the domain name or URI resolve represent the 504 full scope of the mitigation. 506 If there is additional information available narrowing the scope 507 of any requested attack response, such as targeted port range, 508 protocol, or service, DOTS clients SHOULD include that information 509 in client mitigation requests. DOTS clients MAY also include 510 additional attack details. DOTS servers MAY ignore such 511 supplemental information when enabling countermeasures on the 512 mitigator. 514 As an active attack evolves, DOTS clients MUST be able to adjust 515 as necessary the scope of requested mitigation by refining the 516 scope of resources requiring mitigation. 518 A DOTS client may obtain the mitigation scope through direct 519 provisioning or through implementation-specific methods of 520 discovery. DOTS clients MUST support at least one mechanism to 521 obtain mitigation scope. 523 SIG-008 Mitigation Efficacy: When a mitigation request is active, 524 DOTS clients SHOULD transmit a metric of perceived mitigation 525 efficacy to the DOTS server. DOTS servers MAY use the efficacy 526 metric to adjust countermeasures activated on a mitigator on 527 behalf of a DOTS client. 529 SIG-009 Conflict Detection and Notification: Multiple DOTS clients 530 controlled by a single administrative entity may send conflicting 531 mitigation requests for pools of protected resources as a result 532 of misconfiguration, operator error, or compromised DOTS clients. 533 DOTS servers in the same administrative domain attempting to honor 534 conflicting requests may flap network route or DNS information, 535 degrading the networks attempting to participate in attack 536 response with the DOTS clients. DOTS servers in a single 537 administrative domain SHALL detect such conflicting requests, and 538 SHALL notify the DOTS clients in conflict. The notification 539 SHOULD indicate the nature and scope of the conflict, for example, 540 the overlapping prefix range in a conflicting mitigation request. 542 SIG-010: Network Address Translator Traversal: DOTS clients may be 543 deployed behind a Network Address Translator (NAT), and need to 544 communicate with DOTS servers through the NAT. DOTS protocols 545 MUST therefore be capable of traversing NATs. 547 If UDP is used as the transport for the DOTS signal channel, all 548 considerations in "Middlebox Traversal Guidelines" in [RFC8085] 549 apply to DOTS. Regardless of transport, DOTS protocols MUST 550 follow established best common practices (BCPs) for NAT traversal. 552 2.3. Data Channel Requirements 554 The data channel is intended to be used for bulk data exchanges 555 between DOTS agents. Unlike the signal channel, which must operate 556 nominally even when confronted with signal degradation due to packet 557 loss, the data channel is not expected to be constructed to deal with 558 attack conditions. As the primary function of the data channel is 559 data exchange, a reliable transport is required in order for DOTS 560 agents to detect data delivery success or failure. 562 The DOTS data channel protocol MUST be extensible. We anticipate the 563 data channel will be used for such purposes as configuration or 564 resource discovery. For example, a DOTS client may submit to a DOTS 565 server a collection of prefixes it wants to refer to by alias when 566 requesting mitigation, to which the server would respond with a 567 success status and the new prefix group alias, or an error status and 568 message in the event the DOTS client's data channel request failed. 569 The transactional nature of such data exchanges suggests a separate 570 set of requirements for the data channel, while the potentially 571 sensitive content sent between DOTS agents requires extra precautions 572 to ensure data privacy and authenticity. 574 DATA-001 Reliable transport: Messages sent over the data channel 575 MUST be delivered reliably, in order sent. 577 DATA-002 Data privacy and integrity: Transmissions over the data 578 channel are likely to contain operationally or privacy-sensitive 579 information or instructions from the remote DOTS agent. Theft or 580 modification of data channel transmissions could lead to 581 information leaks or malicious transactions on behalf of the 582 sending agent (see Section 4 below). Consequently data sent over 583 the data channel MUST be encrypted and authenticated using current 584 industry best practices. DOTS servers MUST enable means to 585 prevent leaking operationally or privacy-sensitive data. Although 586 administrative entities participating in DOTS may detail what data 587 may be revealed to third-party DOTS agents, such considerations 588 are not in scope for this document. 590 DATA-003 Resource Configuration: To help meet the general and signal 591 channel requirements in Section 2.2, DOTS server implementations 592 MUST provide an interface to configure resource identifiers, as 593 described in SIG-007. DOTS server implementations MAY expose 594 additional configurability. Additional configurability is 595 implementation-specific. 597 DATA-004 Black- and whitelist management: DOTS servers MUST provide 598 methods for DOTS clients to manage black- and white-lists of 599 traffic destined for resources belonging to a client. 601 For example, a DOTS client should be able to create a black- or 602 whitelist entry, retrieve a list of current entries from either 603 list, update the content of either list, and delete entries as 604 necessary. 606 How a DOTS server authorizes DOTS client management of black- and 607 white-list entries is implementation-specific. 609 2.4. Security Requirements 611 DOTS must operate within a particularly strict security context, as 612 an insufficiently protected signal or data channel may be subject to 613 abuse, enabling or supplementing the very attacks DOTS purports to 614 mitigate. 616 SEC-001 Peer Mutual Authentication: DOTS agents MUST authenticate 617 each other before a DOTS signal or data channel is considered 618 valid. The method of authentication is not specified, but should 619 follow current industry best practices with respect to any 620 cryptographic mechanisms to authenticate the remote peer. 622 SEC-002 Message Confidentiality, Integrity and Authenticity: DOTS 623 protocols MUST take steps to protect the confidentiality, 624 integrity and authenticity of messages sent between client and 625 server. While specific transport- and message-level security 626 options are not specified, the protocols MUST follow current 627 industry best practices for encryption and message authentication. 629 In order for DOTS protocols to remain secure despite advancements 630 in cryptanalysis and traffic analysis, DOTS agents MUST be able to 631 negotiate the terms and mechanisms of protocol security, subject 632 to the interoperability and signal message size requirements 633 above. 635 While the interfaces between downstream DOTS server and upstream 636 DOTS client within a DOTS gateway are implementation-specific, 637 those interfaces nevertheless MUST provide security equivalent to 638 that of the signal channels bridged by gateways in the signaling 639 path. For example, when a DOTS gateway consisting of a DOTS 640 server and DOTS client is running on the same logical device, they 641 must be within the same process security boundary. 643 SEC-003 Message Replay Protection: To prevent a passive attacker 644 from capturing and replaying old messages, and thereby potentially 645 disrupting or influencing the network policy of the receiving DOTS 646 agent's domain, DOTS protocols MUST provide a method for replay 647 detection and prevention. 649 Within the signal channel, messages MUST be uniquely identified 650 such that replayed or duplicated messages may be detected and 651 discarded. Unique mitigation requests MUST be processed at most 652 once. 654 SEC-004 Authorization: DOTS servers MUST authorize all messages from 655 DOTS clients which pertain to mitigation, configuration, 656 filtering, or status. 658 DOTS servers MUST reject mitigation requests with scopes which the 659 DOTS client is not authorized to manage. 661 Likewise, DOTS servers MUST refuse to allow creation, modification 662 or deletion of scope aliases and black-/white-lists when the DOTS 663 client is unauthorized. 665 The modes of authorization are implementation-specific. 667 2.5. Data Model Requirements 669 The value of DOTS is in standardizing a mechanism to permit elements, 670 networks or domains under threat of DDoS attack to request aid 671 mitigating the effects of any such attack. A well-structured DOTS 672 data model is therefore critical to the development of successful 673 DOTS protocols. 675 DM-001: Structure: The data model structure for the DOTS protocol 676 may be described by a single module, or be divided into related 677 collections of hierarchical modules and sub-modules. If the data 678 model structure is split across modules, those distinct modules 679 MUST allow references to describe the overall data model's 680 structural dependencies. 682 DM-002: Versioning: To ensure interoperability between DOTS protocol 683 implementations, data models MUST be versioned. How the protocols 684 represent data model versions is not defined in this document. 686 DM-003: Mitigation Status Representation: The data model MUST 687 provide the ability to represent a request for mitigation and the 688 withdrawal of such a request. The data model MUST also support a 689 representation of currently requested mitigation status, including 690 failures and their causes. 692 DM-004: Mitigation Scope Representation: The data model MUST support 693 representation of a requested mitigation's scope. As mitigation 694 scope may be represented in several different ways, per SIG-007 695 above, the data model MUST be capable of flexible representation 696 of mitigation scope. 698 DM-005: Mitigation Lifetime Representation: The data model MUST 699 support representation of a mitigation request's lifetime, 700 including mitigations with no specified end time. 702 DM-006: Mitigation Efficacy Representation: The data model MUST 703 support representation of a DOTS client's understanding of the 704 efficacy of a mitigation enabled through a mitigation request. 706 DM-007: Acceptable Signal Loss Representation: The data model MUST 707 be able to represent the DOTS agent's preference for acceptable 708 signal loss when establishing a signal channel, as described in 709 GEN-002. 711 DM-008: Heartbeat Interval Representation: The data model MUST be 712 able to represent the DOTS agent's preferred heartbeat interval, 713 which the client may include when establishing the signal channel, 714 as described in SIG-003. 716 DM-009: Relationship to Transport: The DOTS data model MUST NOT 717 depend on the specifics of any transport to represent fields in 718 the model. 720 3. Congestion Control Considerations 722 3.1. Signal Channel 724 As part of a protocol expected to operate over links affected by DDoS 725 attack traffic, the DOTS signal channel MUST NOT contribute 726 significantly to link congestion. To meet the signal channel 727 requirements above, DOTS signal channel implementations SHOULD 728 support connectionless transports. However, some connectionless 729 transports when deployed naively can be a source of network 730 congestion, as discussed in [RFC5405]. Signal channel 731 implementations using such connectionless transports, such as UDP, 732 therefore MUST include a congestion control mechanism. 734 Signal channel implementations using TCP may rely on built-in TCP 735 congestion control support. 737 3.2. Data Channel 739 As specified in DATA-001, the data channel requires reliable, in- 740 order message delivery. Data channel implementations using TCP may 741 rely on the TCP implementation's built-in congestion control 742 mechanisms. 744 4. Security Considerations 746 DOTS is at risk from three primary attacks: 748 o DOTS agent impersonation 750 o Traffic injection 752 o Signaling blocking 754 The DOTS protocol MUST be designed for minimal data transfer to 755 address the blocking risk. Impersonation and traffic injection 756 mitigation can be managed through current secure communications best 757 practices. See Section 2.4 above for a detailed discussion. 759 5. Contributors 761 Mohamed Boucadair 762 Orange 764 mohamed.boucadair@orange.com 766 Flemming Andreasen 767 Cisco Systems, Inc. 769 fandreas@cisco.com 771 Dave Dolson 772 Sandvine 774 ddolson@sandvine.com 776 6. Acknowledgments 778 Thanks to Roman Danyliw and Matt Richardson for careful reading and 779 feedback. 781 7. References 783 7.1. Normative References 785 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 786 DOI 10.17487/RFC0768, August 1980, 787 . 789 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 790 DOI 10.17487/RFC0791, September 1981, 791 . 793 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 794 RFC 793, DOI 10.17487/RFC0793, September 1981, 795 . 797 [RFC1035] Mockapetris, P., "Domain names - implementation and 798 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 799 November 1987, . 801 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 802 Communication Layers", STD 3, RFC 1122, 803 DOI 10.17487/RFC1122, October 1989, 804 . 806 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 807 DOI 10.17487/RFC1191, November 1990, 808 . 810 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 811 Requirement Levels", BCP 14, RFC 2119, 812 DOI 10.17487/RFC2119, March 1997, 813 . 815 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 816 Resource Identifier (URI): Generic Syntax", STD 66, 817 RFC 3986, DOI 10.17487/RFC3986, January 2005, 818 . 820 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 821 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 822 2006, . 824 [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing 825 (CIDR): The Internet Address Assignment and Aggregation 826 Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August 827 2006, . 829 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 830 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 831 . 833 [RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines 834 for Application Designers", RFC 5405, 835 DOI 10.17487/RFC5405, November 2008, 836 . 838 [RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage 839 Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, 840 March 2017, . 842 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 843 Address Text Representation", RFC 5952, 844 DOI 10.17487/RFC5952, August 2010, 845 . 847 7.2. Informative References 849 [I-D.ietf-dots-architecture] 850 Mortensen, A., Andreasen, F., Reddy, T., 851 christopher_gray3@cable.comcast.com, c., Compton, R., and 852 N. Teague, "Distributed-Denial-of-Service Open Threat 853 Signaling (DOTS) Architecture", draft-ietf-dots- 854 architecture-05 (work in progress), October 2017. 856 [I-D.ietf-dots-use-cases] 857 Dobbins, R., Migault, D., Fouant, S., Moskowitz, R., 858 Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS 859 Open Threat Signaling", draft-ietf-dots-use-cases-09 (work 860 in progress), November 2017. 862 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 863 A., Peterson, J., Sparks, R., Handley, M., and E. 864 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 865 DOI 10.17487/RFC3261, June 2002, 866 . 868 [RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session 869 Initiation Protocol (SIP) Back-to-Back User Agents", 870 RFC 7092, DOI 10.17487/RFC7092, December 2013, 871 . 873 [RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet 874 Denial-of-Service Considerations", RFC 4732, 875 DOI 10.17487/RFC4732, December 2006, 876 . 878 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", 879 FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, 880 . 882 Authors' Addresses 884 Andrew Mortensen 885 Arbor Networks 886 2727 S. State St 887 Ann Arbor, MI 48104 888 United States 890 Email: amortensen@arbor.net 891 Robert Moskowitz 892 Huawei 893 Oak Park, MI 42837 894 United States 896 Email: rgm@htt-consult.com 898 Tirumaleswar Reddy 899 McAfee, Inc. 900 Embassy Golf Link Business Park 901 Bangalore, Karnataka 560071 902 India 904 Email: TirumaleswarReddy_Konda@McAfee.com