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(The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document date (October 22, 2018) is 2006 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 793 (Obsoleted by RFC 9293) == Outdated reference: A later version (-18) exists of draft-ietf-dots-architecture-07 == Outdated reference: A later version (-25) exists of draft-ietf-dots-use-cases-16 Summary: 1 error (**), 0 flaws (~~), 4 warnings (==), 1 comment (--).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: April 25, 2019 Huawei 6 T. Reddy 7 McAfee 8 October 22, 2018 10 Distributed Denial of Service (DDoS) Open Threat Signaling Requirements 11 draft-ietf-dots-requirements-16 13 Abstract 15 This document defines the requirements for the Distributed Denial of 16 Service (DDoS) Open Threat Signaling (DOTS) protocols enabling 17 coordinated response to 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 April 25, 2019. 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 . . . . . . . . . . . . . . . . . . 6 58 2.2. Signal Channel Requirements . . . . . . . . . . . . . . . 7 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. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 67 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 17 68 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 69 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 70 8.1. Normative References . . . . . . . . . . . . . . . . . . 18 71 8.2. Informative References . . . . . . . . . . . . . . . . . 19 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 74 1. Introduction 76 1.1. Context and Motivation 78 Distributed Denial of Service (DDoS) attacks afflict networks of all 79 kinds, plaguing network operators at service providers and 80 enterprises around the world. High-volume attacks saturating inbound 81 links are now common, as attack scale and frequency continue to 82 increase. 84 The prevalence and impact of these DDoS attacks has led to an 85 increased focus on coordinated attack response. However, many 86 enterprises lack the resources or expertise to operate on-premises 87 attack mitigation solutions themselves, or are constrained by local 88 bandwidth limitations. To address such gaps, service providers have 89 begun to offer on-demand traffic scrubbing services, which are 90 designed to separate the DDoS attack traffic from legitimate traffic 91 and forward only the latter. 93 Today, these services offer proprietary interfaces for subscribers to 94 request attack mitigation. Such proprietary interfaces tie a 95 subscriber to a service while also limiting the network elements 96 capable of participating in the attack mitigation. As a result of 97 signaling interface incompatibility, attack responses may be 98 fragmented or otherwise incomplete, leaving operators in the attack 99 path unable to assist in the defense. 101 A standardized method to coordinate a real-time response among 102 involved operators will increase the speed and effectiveness of DDoS 103 attack mitigation, and reduce the impact of these attacks. This 104 document describes the required characteristics of protocols that 105 enable attack response coordination and mitigation of DDoS attacks. 107 DDoS Open Threat Signaling (DOTS) communicates the need for defensive 108 action in anticipation of or in response to an attack, but does not 109 dictate the implementation of these actions. The requirements in 110 this document are derived from [I-D.ietf-dots-use-cases] and 111 [I-D.ietf-dots-architecture]. 113 1.2. Terminology 115 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 116 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 117 document are to be interpreted as described in BCP14 [RFC2119] 118 [RFC8174], when, and only when, they appear in all capitals. 120 This document adopts the following terms: 122 DDoS: A distributed denial-of-service attack, in which traffic 123 originating from multiple sources is directed at a target on a 124 network. DDoS attacks are intended to cause a negative impact on 125 the availability and/or other functionality of an attack target. 126 Denial-of-service considerations are discussed in detail in 127 [RFC4732]. 129 DDoS attack target: A network connected entity with a finite set of 130 resources, such as network bandwidth, memory or CPU, that is the 131 target of a DDoS attack. Potential targets include (but are not 132 limited to) network elements, network links, servers, and 133 services. 135 DDoS attack telemetry: Collected measurements and behavioral 136 characteristics defining the nature of a DDoS attack. 138 Countermeasure: An action or set of actions focused on recognizing 139 and filtering out specific types of DDoS attack traffic while 140 passing legitimate traffic to the attack target. Distinct 141 countermeasures can be layered to defend against attacks combining 142 multiple DDoS attack types. 144 Mitigation: A set of countermeasures enforced against traffic 145 destined for the target or targets of a detected or reported DDoS 146 attack, where countermeasure enforcement is managed by an entity 147 in the network path between attack sources and the attack target. 148 Mitigation methodology is out of scope for this document. 150 Mitigator: An entity, typically a network element, capable of 151 performing mitigation of a detected or reported DDoS attack. The 152 means by which this entity performs these mitigations and how they 153 are requested of it are out of scope for this document. The 154 mitigator and DOTS server receiving a mitigation request are 155 assumed to belong to the same administrative entity. 157 DOTS client: A DOTS-aware software module responsible for requesting 158 attack response coordination with other DOTS-aware elements. 160 DOTS server: A DOTS-aware software module handling and responding to 161 messages from DOTS clients. The DOTS server enables mitigation on 162 behalf of the DOTS client, if requested, by communicating the DOTS 163 client's request to the mitigator and returning selected mitigator 164 feedback to the requesting DOTS client. 166 DOTS agent: Any DOTS-aware software module capable of participating 167 in a DOTS signal or data channel. It can be a DOTS client, DOTS 168 server, or, as a logical agent, a DOTS gateway. 170 DOTS gateway: A DOTS-aware software module resulting from the 171 logical concatenation of the functionality of a DOTS server and a 172 DOTS client into a single DOTS agent. This functionality is 173 analogous to a Session Initiation Protocol (SIP) [RFC3261] Back- 174 to-Back User Agent (B2BUA) [RFC7092]. A DOTS gateway has a 175 client-facing side, which behaves as a DOTS server for downstream 176 clients, and a server-facing side, which performs the role of DOTS 177 client for upstream DOTS servers. Client-domain DOTS gateways are 178 DOTS gateways that are in the DOTS client's domain, while server- 179 domain DOTS gateways denote DOTS gateways that are in the DOTS 180 server's domain. DOTS gateways are described further in 181 [I-D.ietf-dots-architecture]. 183 Signal channel: A bidirectional, mutually authenticated 184 communication channel between DOTS agents that is resilient even 185 in conditions leading to severe packet loss, such as a volumetric 186 DDoS attack causing network congestion. 188 DOTS signal: A concise status/control message transmitted over the 189 authenticated signal channel between DOTS agents, used to indicate 190 the client's need for mitigation, or to convey the status of any 191 requested mitigation. 193 Heartbeat: A message transmitted between DOTS agents over the signal 194 channel, used as a keep-alive and to measure peer health. 196 Data channel: A bidirectional, mutually authenticated communication 197 channel between two DOTS agents used for infrequent but reliable 198 bulk exchange of data not easily or appropriately communicated 199 through the signal channel. Reliable bulk data exchange may not 200 function well or at all during attacks causing network congestion. 201 The data channel is not expected to operate in such conditions. 203 Filter: A specification of a matching network traffic flow or set of 204 flows. The filter will typically have a policy associated with 205 it, e.g., rate-limiting or discarding matching traffic [RFC4949]. 207 Drop-list: A list of filters indicating sources from which traffic 208 should be blocked, regardless of traffic content. 210 Accept-list: A list of filters indicating sources from which traffic 211 should always be allowed, regardless of contradictory data gleaned 212 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. Once a relationship between DOTS agents 233 is established, regular communication between DOTS clients and 234 servers enables a common understanding of the DOTS agents' health and 235 activity. 237 The DOTS protocol must at a minimum make it possible for a DOTS 238 client to request aid mounting a defense against a suspected attack. 239 This defense could be coordinated by a DOTS server and include 240 signaling within or between domains as requested by local operators. 242 DOTS clients should similarly be able to withdraw aid requests. DOTS 243 requires no justification from DOTS clients for requests for help, 244 nor do DOTS clients need to justify withdrawing help requests: the 245 decision is local to the DOTS clients' domain. Multi-homed DOTS 246 clients must be able to select the appropriate DOTS server(s) to 247 which a mitigation request is to be sent. The method for selecting 248 the appropriate DOTS server in a multi-homed environment is out of 249 scope for this document. 251 DOTS protocol implementations face competing operational goals when 252 maintaining this bidirectional communication stream. On the one 253 hand, DOTS must include measures to ensure message confidentiality, 254 integrity, authenticity, and replay protection to keep the protocols 255 from becoming additional vectors for the very attacks it is meant to 256 help fight off. On the other hand, the protocol must be resilient 257 under extremely hostile network conditions, providing continued 258 contact between DOTS agents even as attack traffic saturates the 259 link. Such resiliency may be developed several ways, but 260 characteristics such as small message size, asynchronous, redundant 261 message delivery and minimal connection overhead (when possible given 262 local network policy) will tend to contribute to the robustness 263 demanded by a viable DOTS protocol. Operators of peer DOTS-enabled 264 domains may enable quality- or class-of-service traffic tagging to 265 increase the probability of successful DOTS signal delivery, but DOTS 266 does not require such policies be in place, and should be viable in 267 their absence. 269 The DOTS server and client must also have some standardized method of 270 defining the scope of any mitigation, as well as managing other 271 mitigation-related configuration. 273 Finally, DOTS should be sufficiently extensible to meet future needs 274 in coordinated attack defense, although this consideration is 275 necessarily superseded by the other operational requirements. 277 2.1. General Requirements 279 GEN-001 Extensibility: Protocols and data models developed as part 280 of DOTS MUST be extensible in order to keep DOTS adaptable to 281 operational and proprietary DDoS defenses. Future extensions MUST 282 be backward compatible. Implementations of older protocol 283 versions SHOULD ignore information added to DOTS messages as part 284 of newer protocol versions. 286 GEN-002 Resilience and Robustness: The signaling protocol MUST be 287 designed to maximize the probability of signal delivery even under 288 the severely constrained network conditions caused by attack 289 traffic. The protocol MUST be resilient, that is, continue 290 operating despite message loss and out-of-order or redundant 291 message delivery. In support of signaling protocol robustness, 292 DOTS signals SHOULD be conveyed over a transport not susceptible 293 to Head of Line Blocking. 295 GEN-003 Bulk Data Exchange: Infrequent bulk data exchange between 296 DOTS agents can also significantly augment attack response 297 coordination, permitting such tasks as population of drop- or 298 accept-listed source addresses; address or prefix group aliasing; 299 exchange of incident reports; and other hinting or configuration 300 supplementing attack response. 302 As the resilience requirements for the DOTS signal channel mandate 303 small signal message size, a separate, secure data channel 304 utilizing a reliable transport protocol MUST be used for bulk data 305 exchange. However, reliable bulk data exchange may not be 306 possible during attacks causing network congestion. 308 GEN-004 Mitigation Hinting: DOTS clients may have access to attack 309 details which can be used to inform mitigation techniques. 310 Example attack details might include locally collected 311 fingerprints for an on-going attack, or anticipated or active 312 attack focal points based on other threat intelligence. DOTS 313 clients MAY send mitigation hints derived from attack details to 314 DOTS servers, in the full understanding that the DOTS server MAY 315 ignore mitigation hints. Mitigation hints MUST be transmitted 316 across the signal channel, as the data channel may not be 317 functional during an attack. DOTS server handling of mitigation 318 hints is implementation-specific. 320 GEN-005 Loop Handling: In certain scenarios, typically involving 321 misconfiguration of DNS or routing policy, it may be possible for 322 communication between DOTS agents to loop. Signal and data 323 channel implementations should be prepared to detect and terminate 324 such loops to prevent service disruption. 326 2.2. Signal Channel Requirements 328 SIG-001 Use of Common Transport Protocols: DOTS MUST operate over 329 common widely deployed and standardized transport protocols. 330 While connectionless transport such as the User Datagram Protocol 331 (UDP) [RFC0768] SHOULD be used for the signal channel, the 332 Transmission Control Protocol (TCP) [RFC0793] MAY be used if 333 necessary due to network policy or middlebox capabilities or 334 configurations. 336 SIG-002 Sub-MTU Message Size: To avoid message fragmentation and the 337 consequently decreased probability of message delivery over a 338 congested link, signaling protocol message size MUST be kept under 339 signaling Path Maximum Transmission Unit (PMTU), including the 340 byte overhead of any encapsulation, transport headers, and 341 transport- or message-level security. 343 DOTS agents SHOULD attempt to learn the PMTU through mechanisms 344 such as Path MTU Discovery [RFC1191] or Packetization Layer Path 345 MTU Discovery [RFC4821]. If the PMTU cannot be discovered, DOTS 346 agents SHOULD assume a PMTU of 1280 bytes. If IPv4 support on 347 legacy or otherwise unusual networks is a consideration and the 348 PMTU is unknown, DOTS implementations MAY rely on a PMTU of 576 349 bytes, as discussed in [RFC0791] and [RFC1122]. 351 SIG-003 Bidirectionality: To support peer health detection, to 352 maintain an active signal channel, and to increase the probability 353 of signal delivery during an attack, the signal channel MUST be 354 bidirectional, with client and server transmitting signals to each 355 other at regular intervals, regardless of any client request for 356 mitigation. The bidirectional signal channel MUST support 357 unidirectional messaging to enable notifications between DOTS 358 agents. 360 SIG-004 Channel Health Monitoring: DOTS agents MUST support exchange 361 of heartbeat messages over the signal channel to monitor channel 362 health. Peer DOTS agents SHOULD regularly send heartbeats to each 363 other while a mitigation request is active. The heartbeat 364 interval during active mitigation could be negotiable, but SHOULD 365 be frequent enough to maintain any on-path NAT or Firewall 366 bindings during mitigation. 368 To support scenarios in which loss of heartbeat is used to trigger 369 mitigation, and to keep the channel active, DOTS clients MAY 370 solicit heartbeat exchanges after successful mutual 371 authentication. When DOTS agents are exchanging heartbeats and no 372 mitigation request is active, either agent MAY request changes to 373 the heartbeat rate. For example, a DOTS server might want to 374 reduce heartbeat frequency or cease heartbeat exchanges when an 375 active DOTS client has not requested mitigation, in order to 376 control load. 378 Following mutual authentication, a signal channel MUST be 379 considered active until a DOTS agent explicitly ends the session, 380 or either DOTS agent fails to receive heartbeats from the other 381 after a mutually agreed upon retransmission procedure has been 382 exhausted. Because heartbeat loss is much more likely during 383 volumetric attack, DOTS agents SHOULD avoid signal channel 384 termination when mitigation is active and heartbeats are not 385 received by either DOTS agent for an extended period. In such 386 circumstances, DOTS clients MAY attempt to reestablish the signal 387 channel, but SHOULD continue to send heartbeats so that the DOTS 388 server knows the session is still alive. DOTS servers are assumed 389 to have the ability to monitor the attack, using feedback from the 390 mitigator and other available sources, and MAY use the absence of 391 attack traffic and lack of client heartbeats as an indication the 392 signal channel is defunct. 394 SIG-005 Channel Redirection: In order to increase DOTS operational 395 flexibility and scalability, DOTS servers SHOULD be able to 396 redirect DOTS clients to another DOTS server at any time. DOTS 397 clients MUST NOT assume the redirection target DOTS server shares 398 security state with the redirecting DOTS server. DOTS clients are 399 free to attempt abbreviated security negotiation methods supported 400 by the protocol, such as DTLS session resumption, but MUST be 401 prepared to negotiate new security state with the redirection 402 target DOTS server. The authentication domain of the redirection 403 target DOTS server MUST be the same as the authentication domain 404 of the redirecting DOTS server. 406 Due to the increased likelihood of packet loss caused by link 407 congestion during an attack, DOTS servers SHOULD NOT redirect 408 while mitigation is enabled during an active attack against a 409 target in the DOTS client's domain. 411 SIG-006 Mitigation Requests and Status: Authorized DOTS clients MUST 412 be able to request scoped mitigation from DOTS servers. DOTS 413 servers MUST send status to the DOTS clients about mitigation 414 requests. If a DOTS server rejects an authorized request for 415 mitigation, the DOTS server MUST include a reason for the 416 rejection in the status message sent to the client. 418 Due to the higher likelihood of packet loss during a DDoS attack, 419 DOTS servers SHOULD regularly send mitigation status to authorized 420 DOTS clients which have requested and been granted mitigation, 421 regardless of client requests for mitigation status. 423 When DOTS client-requested mitigation is active, DOTS server 424 status messages SHOULD include the following mitigation metrics: 426 * Total number of packets blocked by the mitigation 428 * Current number of packets per second blocked 430 * Total number of bytes blocked 432 * Current number of bytes per second blocked 433 DOTS clients MAY take these metrics into account when determining 434 whether to ask the DOTS server to cease mitigation. 436 A DOTS client MAY withdraw a mitigation request at any time, 437 regardless of whether mitigation is currently active. The DOTS 438 server MUST immediately acknowledge a DOTS client's request to 439 stop mitigation. 441 To protect against route or DNS flapping caused by a client 442 rapidly toggling mitigation, and to dampen the effect of 443 oscillating attacks, DOTS servers MAY allow mitigation to continue 444 for a limited period after acknowledging a DOTS client's 445 withdrawal of a mitigation request. During this period, DOTS 446 server status messages SHOULD indicate that mitigation is active 447 but terminating. DOTS clients MAY reverse the mitigation 448 termination during this active-but-terminating period with a new 449 mitigation request for the same scope. The DOTS server MUST treat 450 this request as a mitigation lifetime extension (see SIG-007 451 below). 453 The initial active-but-terminating period is implementation- and 454 deployment- specific, but SHOULD be sufficiently long to absorb 455 latency incurred by route propagation. If a DOTS client refreshes 456 the mitigation before the active-but-terminating period elapses, 457 the DOTS server MAY increase the active-but-terminating period up 458 to a maximum of 300 seconds (5 minutes). After the active-but- 459 terminating period elapses, the DOTS server MUST treat the 460 mitigation as terminated, as the DOTS client is no longer 461 responsible for the mitigation. 463 SIG-007 Mitigation Lifetime: DOTS servers MUST support mitigations 464 for a negotiated time interval, and MUST terminate a mitigation 465 when the lifetime elapses. DOTS servers also MUST support renewal 466 of mitigation lifetimes in mitigation requests from DOTS clients, 467 allowing clients to extend mitigation as necessary for the 468 duration of an attack. 470 DOTS servers MUST treat a mitigation terminated due to lifetime 471 expiration exactly as if the DOTS client originating the 472 mitigation had asked to end the mitigation, including the active- 473 but-terminating period, as described above in SIG-005. 475 DOTS clients MUST include a mitigation lifetime in all mitigation 476 requests. 478 DOTS servers SHOULD support indefinite mitigation lifetimes, 479 enabling architectures in which the mitigator is always in the 480 traffic path to the resources for which the DOTS client is 481 requesting protection. DOTS clients MUST be prepared to not be 482 granted mitigations with indefinite lifetimes. DOTS servers MAY 483 refuse mitigations with indefinite lifetimes, for policy reasons. 484 The reasons themselves are out of scope. If the DOTS server does 485 not grant a mitigation request with an indefinite mitigation 486 lifetime, it MUST set the lifetime to a value that is configured 487 locally. That value MUST be returned in a reply to the requesting 488 DOTS client. 490 SIG-008 Mitigation Scope: DOTS clients MUST indicate desired 491 mitigation scope. The scope type will vary depending on the 492 resources requiring mitigation. All DOTS agent implementations 493 MUST support the following required scope types: 495 * IPv4 prefixes [RFC4632] 497 * IPv6 prefixes [RFC4291][RFC5952] 499 * Domain names [RFC1035] 501 The following mitigation scope types are OPTIONAL: 503 * Uniform Resource Identifiers [RFC3986] 505 DOTS servers MUST be able to resolve domain names and (when 506 supported) URIs. How name resolution is managed on the DOTS 507 server is implementation-specific. 509 DOTS agents MUST support mitigation scope aliases, allowing DOTS 510 clients and servers to refer to collections of protected resources 511 by an opaque identifier created through the data channel, direct 512 configuration, or other means. Domain name and URI mitigation 513 scopes may be thought of as a form of scope alias, in which the 514 addresses to which the domain name or URI resolve represent the 515 full scope of the mitigation. 517 If there is additional information available narrowing the scope 518 of any requested attack response, such as targeted port range, 519 protocol, or service, DOTS clients SHOULD include that information 520 in client mitigation requests. DOTS clients MAY also include 521 additional attack details. DOTS servers MAY ignore such 522 supplemental information when enabling countermeasures on the 523 mitigator. 525 As an active attack evolves, DOTS clients MUST be able to adjust 526 as necessary the scope of requested mitigation by refining the 527 scope of resources requiring mitigation. 529 A DOTS client may obtain the mitigation scope through direct 530 provisioning or through implementation-specific methods of 531 discovery. DOTS clients MUST support at least one mechanism to 532 obtain mitigation scope. 534 SIG-009 Mitigation Efficacy: When a mitigation request is active, 535 DOTS clients SHOULD transmit a metric of perceived mitigation 536 efficacy to the DOTS server. DOTS servers MAY use the efficacy 537 metric to adjust countermeasures activated on a mitigator on 538 behalf of a DOTS client. 540 SIG-010 Conflict Detection and Notification: Multiple DOTS clients 541 controlled by a single administrative entity may send conflicting 542 mitigation requests as a result of misconfiguration, operator 543 error, or compromised DOTS clients. DOTS servers in the same 544 administrative domain attempting to honor conflicting requests may 545 flap network route or DNS information, degrading the networks 546 attempting to participate in attack response with the DOTS 547 clients. DOTS servers in a single administrative domain SHALL 548 detect such conflicting requests, and SHALL notify the DOTS 549 clients in conflict. The notification SHOULD indicate the nature 550 and scope of the conflict, for example, the overlapping prefix 551 range in a conflicting mitigation request. 553 SIG-011 Network Address Translator Traversal: DOTS clients may be 554 deployed behind a Network Address Translator (NAT), and need to 555 communicate with DOTS servers through the NAT. DOTS protocols 556 MUST therefore be capable of traversing NATs. 558 If UDP is used as the transport for the DOTS signal channel, all 559 considerations in "Middlebox Traversal Guidelines" in [RFC8085] 560 apply to DOTS. Regardless of transport, DOTS protocols MUST 561 follow established best common practices established in BCP 127 562 for NAT traversal [RFC4787][RFC6888][RFC7857]. 564 2.3. Data Channel Requirements 566 The data channel is intended to be used for bulk data exchanges 567 between DOTS agents. Unlike the signal channel, the data channel is 568 not expected to be constructed to deal with attack conditions. As 569 the primary function of the data channel is data exchange, a reliable 570 transport is required in order for DOTS agents to detect data 571 delivery success or failure. 573 The data channel provides a protocol for DOTS configuration, 574 management. For example, a DOTS client may submit to a DOTS server a 575 collection of prefixes it wants to refer to by alias when requesting 576 mitigation, to which the server would respond with a success status 577 and the new prefix group alias, or an error status and message in the 578 event the DOTS client's data channel request failed. 580 DATA-001 Reliable transport: Messages sent over the data channel 581 MUST be delivered reliably, in order sent. 583 DATA-002 Data privacy and integrity: Transmissions over the data 584 channel are likely to contain operationally or privacy-sensitive 585 information or instructions from the remote DOTS agent. Theft, 586 modification, or replay of data channel transmissions could lead 587 to information leaks or malicious transactions on behalf of the 588 sending agent (see Section 4 below). Consequently data sent over 589 the data channel MUST be encrypted and authenticated using current 590 IETF best practices. DOTS servers MUST enable means to prevent 591 leaking operationally or privacy-sensitive data. Although 592 administrative entities participating in DOTS may detail what data 593 may be revealed to third-party DOTS agents, such considerations 594 are not in scope for this document. 596 DATA-003 Resource Configuration: To help meet the general and signal 597 channel requirements in Section 2.1 and Section 2.2, DOTS server 598 implementations MUST provide an interface to configure resource 599 identifiers, as described in SIG-008. DOTS server implementations 600 MAY expose additional configurability. Additional configurability 601 is implementation-specific. 603 DATA-004 Policy management: DOTS servers MUST provide methods for 604 DOTS clients to manage drop- and accept-lists of traffic destined 605 for resources belonging to a client. 607 For example, a DOTS client should be able to create a drop- or 608 accept-list entry, retrieve a list of current entries from either 609 list, update the content of either list, and delete entries as 610 necessary. 612 How a DOTS server authorizes DOTS client management of drop- and 613 accept-list entries is implementation-specific. 615 2.4. Security Requirements 617 DOTS must operate within a particularly strict security context, as 618 an insufficiently protected signal or data channel may be subject to 619 abuse, enabling or supplementing the very attacks DOTS purports to 620 mitigate. 622 SEC-001 Peer Mutual Authentication: DOTS agents MUST authenticate 623 each other before a DOTS signal or data channel is considered 624 valid. The method of authentication is not specified in this 625 document, but should follow current industry best practices with 626 respect to any cryptographic mechanisms to authenticate the remote 627 peer. 629 SEC-002 Message Confidentiality, Integrity and Authenticity: DOTS 630 protocols MUST take steps to protect the confidentiality, 631 integrity and authenticity of messages sent between client and 632 server. While specific transport- and message-level security 633 options are not specified, the protocols MUST follow current 634 industry best practices for encryption and message authentication. 636 In order for DOTS protocols to remain secure despite advancements 637 in cryptanalysis and traffic analysis, DOTS agents MUST support 638 secure negotiation of the terms and mechanisms of protocol 639 security, subject to the interoperability and signal message size 640 requirements in Section 2.2. 642 While the interfaces between downstream DOTS server and upstream 643 DOTS client within a DOTS gateway are implementation-specific, 644 those interfaces nevertheless MUST provide security equivalent to 645 that of the signal channels bridged by gateways in the signaling 646 path. For example, when a DOTS gateway consisting of a DOTS 647 server and DOTS client is running on the same logical device, the 648 two DOTS agents could be implemented within the same process 649 security boundary. 651 SEC-003 Message Replay Protection: To prevent a passive attacker 652 from capturing and replaying old messages, and thereby potentially 653 disrupting or influencing the network policy of the receiving DOTS 654 agent's domain, DOTS protocols MUST provide a method for replay 655 detection and prevention. 657 Within the signal channel, messages MUST be uniquely identified 658 such that replayed or duplicated messages can be detected and 659 discarded. Unique mitigation requests MUST be processed at most 660 once. 662 SEC-004 Authorization: DOTS servers MUST authorize all messages from 663 DOTS clients which pertain to mitigation, configuration, 664 filtering, or status. 666 DOTS servers MUST reject mitigation requests with scopes which the 667 DOTS client is not authorized to manage. 669 Likewise, DOTS servers MUST refuse to allow creation, modification 670 or deletion of scope aliases and drop-/accept-lists when the DOTS 671 client is unauthorized. 673 The modes of authorization are implementation-specific. 675 2.5. Data Model Requirements 677 A well-structured DOTS data model is critical to the development of 678 successful DOTS protocols. 680 DM-001 Structure: The data model structure for the DOTS protocol MAY 681 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 provide 692 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 include extensible representation of 701 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 be 712 able to represent the DOTS agent's preference for acceptable 713 signal loss when establishing a signal channel, as described in 714 GEN-002. Measurements of loss might include, but are not 715 restricted to, number of consecutive missed heartbeat messages, 716 retransmission count, or request timeouts. 718 DM-008 Heartbeat Interval Representation: The data model MUST be 719 able to represent the DOTS agent's preferred heartbeat interval, 720 which the client may include when establishing the signal channel, 721 as described in SIG-003. 723 DM-009 Relationship to Transport: The DOTS data model MUST NOT 724 depend on the specifics of any transport to represent fields in 725 the model. 727 3. Congestion Control Considerations 729 3.1. Signal Channel 731 As part of a protocol expected to operate over links affected by DDoS 732 attack traffic, the DOTS signal channel MUST NOT contribute 733 significantly to link congestion. To meet the signal channel 734 requirements above, DOTS signal channel implementations SHOULD 735 support connectionless transports. However, some connectionless 736 transports when deployed naively can be a source of network 737 congestion, as discussed in [RFC8085]. Signal channel 738 implementations using such connectionless transports, such as UDP, 739 therefore MUST include a congestion control mechanism. 741 Signal channel implementations using TCP may rely on built-in TCP 742 congestion control support. 744 3.2. Data Channel 746 As specified in DATA-001, the data channel requires reliable, in- 747 order message delivery. Data channel implementations using TCP may 748 rely on the TCP implementation's built-in congestion control 749 mechanisms. 751 4. Security Considerations 753 This document informs future protocols under development, and so does 754 not have security considerations of its own. However, operators 755 should be aware of potential risks involved in deploying DOTS. DOTS 756 agent impersonation and signal blocking are discussed here. 757 Additional DOTS security considerations may be found in 758 [I-D.ietf-dots-architecture] and DOTS protocol documents. 760 Impersonation of either a DOTS server or a DOTS client could have 761 catastrophic impact on operations in either domain. If an attacker 762 has the ability to impersonate a DOTS client, that attacker can 763 affect policy on the network path to the DOTS client's domain, up to 764 and including instantiation of drop-lists blocking all inbound 765 traffic to networks for which the DOTS client is authorized to 766 request mitigation. 768 Similarly, an impersonated DOTS server may be able to act as a sort 769 of malicious DOTS gateway, intercepting requests from the downstream 770 DOTS client, and modifying them before transmission to the DOTS 771 server to inflict the desired impact on traffic to or from the DOTS 772 client's domain. Among other things, this malicious DOTS gateway 773 might receive and discard mitigation requests from the DOTS client, 774 ensuring no requested mitigation is ever applied. 776 As detailed in Section 2.4, DOTS implementations require mutual 777 authentication of DOTS agents in order to make agent impersonation 778 more difficult. However, impersonation may still be possible as a 779 result of credential theft, implementation flaws, or compromise of 780 DOTS agents. To detect misuse, DOTS operators should carefully 781 monitor and audit DOTS agents, while employing current secure network 782 communications best practices to reduce attack surface. 784 Blocking communication between DOTS agents has the potential to 785 disrupt the core function of DOTS, which is to request mitigation of 786 active or expected DDoS attacks. The DOTS signal channel is expected 787 to operate over congested inbound links, and, as described in 788 Section 2.2, the signal channel protocol must be designed for minimal 789 data transfer to reduce the incidence of signal loss. 791 5. IANA Considerations 793 This document does not require any IANA action. 795 6. Contributors 797 Mohamed Boucadair 798 Orange 800 mohamed.boucadair@orange.com 802 Flemming Andreasen 803 Cisco Systems, Inc. 805 fandreas@cisco.com 807 Dave Dolson 808 Sandvine 810 ddolson@sandvine.com 812 7. Acknowledgments 814 Thanks to Roman Danyliw, Matt Richardson, and Jon Shallow for careful 815 reading and feedback. 817 8. References 819 8.1. Normative References 821 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 822 DOI 10.17487/RFC0768, August 1980, 823 . 825 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 826 DOI 10.17487/RFC0791, September 1981, 827 . 829 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 830 RFC 793, DOI 10.17487/RFC0793, September 1981, 831 . 833 [RFC1035] Mockapetris, P., "Domain names - implementation and 834 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 835 November 1987, . 837 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 838 Communication Layers", STD 3, RFC 1122, 839 DOI 10.17487/RFC1122, October 1989, 840 . 842 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 843 DOI 10.17487/RFC1191, November 1990, 844 . 846 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 847 Requirement Levels", BCP 14, RFC 2119, 848 DOI 10.17487/RFC2119, March 1997, 849 . 851 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 852 Resource Identifier (URI): Generic Syntax", STD 66, 853 RFC 3986, DOI 10.17487/RFC3986, January 2005, 854 . 856 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 857 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 858 2006, . 860 [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing 861 (CIDR): The Internet Address Assignment and Aggregation 862 Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August 863 2006, . 865 [RFC4787] Audet, F., Ed. and C. Jennings, "Network Address 866 Translation (NAT) Behavioral Requirements for Unicast 867 UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January 868 2007, . 870 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 871 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 872 . 874 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 875 Address Text Representation", RFC 5952, 876 DOI 10.17487/RFC5952, August 2010, 877 . 879 [RFC6888] Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa, 880 A., and H. Ashida, "Common Requirements for Carrier-Grade 881 NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888, 882 April 2013, . 884 [RFC7857] Penno, R., Perreault, S., Boucadair, M., Ed., Sivakumar, 885 S., and K. Naito, "Updates to Network Address Translation 886 (NAT) Behavioral Requirements", BCP 127, RFC 7857, 887 DOI 10.17487/RFC7857, April 2016, 888 . 890 [RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage 891 Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, 892 March 2017, . 894 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 895 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 896 May 2017, . 898 8.2. Informative References 900 [I-D.ietf-dots-architecture] 901 Mortensen, A., Andreasen, F., K, R., 902 christopher_gray3@cable.comcast.com, c., Compton, R., and 903 N. Teague, "Distributed-Denial-of-Service Open Threat 904 Signaling (DOTS) Architecture", draft-ietf-dots- 905 architecture-07 (work in progress), September 2018. 907 [I-D.ietf-dots-use-cases] 908 Dobbins, R., Migault, D., Fouant, S., Moskowitz, R., 909 Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS 910 Open Threat Signaling", draft-ietf-dots-use-cases-16 (work 911 in progress), July 2018. 913 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 914 A., Peterson, J., Sparks, R., Handley, M., and E. 915 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 916 DOI 10.17487/RFC3261, June 2002, 917 . 919 [RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session 920 Initiation Protocol (SIP) Back-to-Back User Agents", 921 RFC 7092, DOI 10.17487/RFC7092, December 2013, 922 . 924 [RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet 925 Denial-of-Service Considerations", RFC 4732, 926 DOI 10.17487/RFC4732, December 2006, 927 . 929 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", 930 FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, 931 . 933 Authors' Addresses 935 Andrew Mortensen 936 Arbor Networks 937 2727 S. State St 938 Ann Arbor, MI 48104 939 United States 941 Email: amortensen@arbor.net 943 Robert Moskowitz 944 Huawei 945 Oak Park, MI 42837 946 United States 948 Email: rgm@htt-consult.com 949 Tirumaleswar Reddy 950 McAfee 951 Embassy Golf Link Business Park 952 Bangalore, Karnataka 560071 953 India 955 Email: TirumaleswarReddy_Konda@McAfee.com