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(The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document date (February 2, 2019) is 1903 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** Obsolete normative reference: RFC 793 (Obsoleted by RFC 9293) == Outdated reference: A later version (-18) exists of draft-ietf-dots-architecture-10 == Outdated reference: A later version (-25) exists of draft-ietf-dots-use-cases-17 == Outdated reference: A later version (-17) exists of draft-ietf-intarea-frag-fragile-08 Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 1 comment (--).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 T. Reddy 5 Expires: August 6, 2019 McAfee 6 R. Moskowitz 7 Huawei 8 February 2, 2019 10 Distributed Denial of Service (DDoS) Open Threat Signaling Requirements 11 draft-ietf-dots-requirements-18 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 August 6, 2019. 36 Copyright Notice 38 Copyright (c) 2019 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 . . . . . . . . . . . . . . . 8 59 2.3. Data Channel Requirements . . . . . . . . . . . . . . . . 13 60 2.4. Security Requirements . . . . . . . . . . . . . . . . . . 14 61 2.5. Data Model Requirements . . . . . . . . . . . . . . . . . 15 62 3. Congestion Control Considerations . . . . . . . . . . . . . . 16 63 3.1. Signal Channel . . . . . . . . . . . . . . . . . . . . . 16 64 3.2. Data Channel . . . . . . . . . . . . . . . . . . . . . . 17 65 4. Security Considerations . . . . . . . . . . . . . . . . . . . 17 66 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 67 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 18 68 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 69 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 70 8.1. Normative References . . . . . . . . . . . . . . . . . . 18 71 8.2. Informative References . . . . . . . . . . . . . . . . . 20 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 74 1. Introduction 76 1.1. Context and Motivation 78 Distributed Denial of Service (DDoS) attacks afflict networks 79 connected to the Internet, plaguing network operators at service 80 providers and enterprises around the world. High-volume attacks 81 saturating inbound links are now common, as attack scale and 82 frequency continue to 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 and limit the abilities of network elements 96 that would otherwise be capable of participating in attack 97 mitigation. As a result of signaling interface incompatibility, 98 attack responses may be fragmented or otherwise incomplete, leaving 99 operators in the attack 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 that is the target of 130 a DDoS attack. Potential targets include (but are not limited to) 131 network elements, network links, servers, and services. 133 DDoS attack telemetry: Collected measurements and behavioral 134 characteristics defining the nature of a DDoS attack. 136 Countermeasure: An action or set of actions focused on recognizing 137 and filtering out specific types of DDoS attack traffic while 138 passing legitimate traffic to the attack target. Distinct 139 countermeasures can be layered to defend against attacks combining 140 multiple DDoS attack types. 142 Mitigation: A set of countermeasures enforced against traffic 143 destined for the target or targets of a detected or reported DDoS 144 attack, where countermeasure enforcement is managed by an entity 145 in the network path between attack sources and the attack target. 146 Mitigation methodology is out of scope for this document. 148 Mitigator: An entity, typically a network element, capable of 149 performing mitigation of a detected or reported DDoS attack. The 150 means by which this entity performs these mitigations and how they 151 are requested of it are out of scope for this document. The 152 mitigator and DOTS server receiving a mitigation request are 153 assumed to belong to the same administrative entity. 155 DOTS client: A DOTS-aware software module responsible for requesting 156 attack response coordination with other DOTS-aware elements. 158 DOTS server: A DOTS-aware software module handling and responding to 159 messages from DOTS clients. The DOTS server enables mitigation on 160 behalf of the DOTS client, if requested, by communicating the DOTS 161 client's request to the mitigator and returning selected mitigator 162 feedback to the requesting DOTS client. 164 DOTS agent: Any DOTS-aware software module capable of participating 165 in a DOTS signal or data channel. It can be a DOTS client, DOTS 166 server, or, as a logical agent, a DOTS gateway. 168 DOTS gateway: A DOTS-aware software module resulting from the 169 logical concatenation of the functionality of a DOTS server and a 170 DOTS client into a single DOTS agent. This functionality is 171 analogous to a Session Initiation Protocol (SIP) [RFC3261] Back- 172 to-Back User Agent (B2BUA) [RFC7092]. A DOTS gateway has a 173 client-facing side, which behaves as a DOTS server for downstream 174 clients, and a server-facing side, which performs the role of DOTS 175 client for upstream DOTS servers. Client-domain DOTS gateways are 176 DOTS gateways that are in the DOTS client's domain, while server- 177 domain DOTS gateways denote DOTS gateways that are in the DOTS 178 server's domain. A DOTS gateway may terminate multiple discrete 179 DOTS client connections and may aggregate these into a single or 180 multiple connections. 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 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 The expected layout and interactions amongst DOTS entities is 220 described in the DOTS Architecture [I-D.ietf-dots-architecture]. 222 The goal of the DOTS requirements specification is to specify the 223 requirements for DOTS signal channel and data channel protocols that 224 have different application and transport layer requirements. This 225 section describes the required features and characteristics of the 226 DOTS protocols. 228 The goal of DOTS protocols is to enable and manage mitigation on 229 behalf of a network domain or resource which is or may become the 230 focus of a DDoS attack. An active DDoS attack against the entity 231 controlling the DOTS client need not be present before establishing a 232 communication channel between DOTS agents. Indeed, establishing a 233 relationship with peer DOTS agents during normal network conditions 234 provides the foundation for more rapid attack response against future 235 attacks, as all interactions setting up DOTS, including any business 236 or service level agreements, are already complete. Reachability 237 information of peer DOTS agents is provisioned to a DOTS client using 238 a variety of manual or dynamic methods. Once a relationship between 239 DOTS agents is established, regular communication between DOTS 240 clients and servers enables a common understanding of the DOTS 241 agents' health and activity. 243 The DOTS protocol must at a minimum make it possible for a DOTS 244 client to request aid mounting a defense against a suspected attack. 245 This defense could be coordinated by a DOTS server and include 246 signaling within or between domains as requested by local operators. 247 DOTS clients should similarly be able to withdraw aid requests. DOTS 248 requires no justification from DOTS clients for requests for help, 249 nor do DOTS clients need to justify withdrawing help requests: the 250 decision is local to the DOTS clients' domain. Multi-homed DOTS 251 clients must be able to select the appropriate DOTS server(s) to 252 which a mitigation request is to be sent. The method for selecting 253 the appropriate DOTS server in a multi-homed environment is out of 254 scope for this document. 256 DOTS protocol implementations face competing operational goals when 257 maintaining this bidirectional communication stream. On the one 258 hand, DOTS must include measures to ensure message confidentiality, 259 integrity, authenticity, and replay protection to keep the protocols 260 from becoming additional vectors for the very attacks it is meant to 261 help fight off. On the other hand, the protocol must be resilient 262 under extremely hostile network conditions, providing continued 263 contact between DOTS agents even as attack traffic saturates the 264 link. Such resiliency may be developed several ways, but 265 characteristics such as small message size, asynchronous, redundant 266 message delivery and minimal connection overhead (when possible given 267 local network policy) will tend to contribute to the robustness 268 demanded by a viable DOTS protocol. Operators of peer DOTS-enabled 269 domains may enable quality- or class-of-service traffic tagging to 270 increase the probability of successful DOTS signal delivery, but DOTS 271 does not require such policies be in place, and should be viable in 272 their absence. 274 The DOTS server and client must also have some standardized method of 275 defining the scope of any mitigation, as well as managing other 276 mitigation-related configuration. 278 Finally, DOTS should be sufficiently extensible to meet future needs 279 in coordinated attack defense, although this consideration is 280 necessarily superseded by the other operational requirements. 282 2.1. General Requirements 284 GEN-001 Extensibility: Protocols and data models developed as part 285 of DOTS MUST be extensible in order to keep DOTS adaptable to 286 proprietary DDoS defenses. Future extensions MUST be backward 287 compatible. Implementations of older protocol versions MUST 288 ignore optional information added to DOTS messages as part of 289 newer protocol versions. Implementations of older protocol 290 versions MUST reject mandatory information added to DOTS messages 291 as part of newer protocol versions. 293 GEN-002 Resilience and Robustness: The signaling protocol MUST be 294 designed to maximize the probability of signal delivery even under 295 the severely constrained network conditions caused by attack 296 traffic. Additional means to enhance the resilience of DOTS 297 protocols, including when multiple DOTS servers are provisioned to 298 the DOTS clients, SHOULD be considered. The protocol MUST be 299 resilient, that is, continue operating despite message loss and 300 out-of-order or redundant message delivery. In support of 301 signaling protocol robustness, DOTS signals SHOULD be conveyed 302 over transport and application protocols not susceptible to Head 303 of Line Blocking. These requirements are at SHOULD strength to 304 handle middle-boxes and firewall traversal. 306 GEN-003 Bulk Data Exchange: Infrequent bulk data exchange between 307 DOTS agents can also significantly augment attack response 308 coordination, permitting such tasks as population of drop- or 309 accept-listed source addresses; address or prefix group aliasing; 310 exchange of incident reports; and other hinting or configuration 311 supplementing attack response. 313 As the resilience requirements for the DOTS signal channel mandate 314 small signal message size, a separate, secure data channel 315 utilizing a reliable transport protocol MUST be used for bulk data 316 exchange. However, reliable bulk data exchange may not be 317 possible during attacks causing network congestion. 319 GEN-004 Mitigation Hinting: DOTS clients may have access to attack 320 details which can be used to inform mitigation techniques. 321 Example attack details might include locally collected 322 fingerprints for an on-going attack, or anticipated or active 323 attack focal points based on other threat intelligence. DOTS 324 clients MAY send mitigation hints derived from attack details to 325 DOTS servers, in the full understanding that the DOTS server MAY 326 ignore mitigation hints. Mitigation hints MUST be transmitted 327 across the signal channel, as the data channel may not be 328 functional during an attack. DOTS server handling of mitigation 329 hints is implementation-specific. 331 GEN-005 Loop Handling: In certain scenarios, typically involving 332 misconfiguration of DNS or routing policy, it may be possible for 333 communication between DOTS agents to loop. Signal and data 334 channel implementations should be prepared to detect and terminate 335 such loops to prevent service disruption. 337 2.2. Signal Channel Requirements 339 SIG-001 Use of Common Transport Protocols: DOTS MUST operate over 340 common widely deployed and standardized transport protocols. 341 While connectionless transport such as the User Datagram Protocol 342 (UDP) [RFC0768] SHOULD be used for the signal channel, the 343 Transmission Control Protocol (TCP) [RFC0793] MAY be used if 344 necessary due to network policy or middlebox capabilities or 345 configurations. 347 SIG-002 Sub-MTU Message Size: To avoid message fragmentation and the 348 consequently decreased probability of message delivery over a 349 congested link, signaling protocol message size MUST be kept under 350 signaling Path Maximum Transmission Unit (PMTU), including the 351 byte overhead of any encapsulation, transport headers, and 352 transport- or message-level security. 354 DOTS agents can attempt to learn PMTU using the procedures 355 discussed in [I-D.ietf-intarea-frag-fragile]. If the PMTU cannot 356 be discovered, DOTS agents MUST assume a PMTU of 1280 bytes for 357 IPv6. If IPv4 support on legacy or otherwise unusual networks is 358 a consideration and the PMTU is unknown, DOTS implementations MAY 359 rely on a PMTU of 576 bytes for IPv4 datagrams, as discussed in 360 [RFC0791] and [RFC1122]. 362 SIG-003 Bidirectionality: To support peer health detection, to 363 maintain an active signal channel, and to increase the probability 364 of signal delivery during an attack, the signal channel MUST be 365 bidirectional, with client and server transmitting signals to each 366 other at regular intervals, regardless of any client request for 367 mitigation. The bidirectional signal channel MUST support 368 unidirectional messaging to enable notifications between DOTS 369 agents. 371 SIG-004 Channel Health Monitoring: DOTS agents MUST support exchange 372 of heartbeat messages over the signal channel to monitor channel 373 health. The heartbeat interval during active mitigation could be 374 negotiable, but MUST be frequent enough to maintain any on-path 375 NAT or Firewall bindings during mitigation. When TCP is used as 376 transport, the DOTS signal channel heartbeat messages need to be 377 frequent enough to maintain the TCP connection state. 379 To support scenarios in which loss of heartbeat is used to trigger 380 mitigation, and to keep the channel active, DOTS server MUST 381 solicit heartbeat exchanges after successful mutual 382 authentication. When DOTS agents are exchanging heartbeats and no 383 mitigation request is active, either agent MAY request changes to 384 the heartbeat rate. For example, a DOTS server might want to 385 reduce heartbeat frequency or cease heartbeat exchanges when an 386 active DOTS client has not requested mitigation, in order to 387 control load. 389 Following mutual authentication, a signal channel MUST be 390 considered active until a DOTS agent explicitly ends the session. 391 During peace time, signal channel MUST be considered active until 392 either DOTS agent fails to receive heartbeats from the other after 393 a mutually agreed upon retransmission procedure has been 394 exhausted. Peer DOTS agents MUST regularly send heartbeats to 395 each other while a mitigation request is active. Because 396 heartbeat loss is much more likely during volumetric attack, DOTS 397 agents SHOULD avoid signal channel termination when mitigation is 398 active and heartbeats are not received by either DOTS agent for an 399 extended period. The exception circumstances to terminate the 400 signal channel session during active mitigation are discussed 401 below: 403 * To handle possible DOTS server restart or crash, the DOTS 404 clients MAY attempt to establish a new signal channel session, 405 but MUST continue to send heartbeats on the current session so 406 that the DOTS server knows the session is still alive. If the 407 new session is successfully established, the DOTS client can 408 terminate the current session. 410 * DOTS servers are assumed to have the ability to monitor the 411 attack, using feedback from the mitigator and other available 412 sources, and MAY use the absence of attack traffic and lack of 413 client heartbeats as an indication the signal channel is 414 defunct. 416 SIG-005 Channel Redirection: In order to increase DOTS operational 417 flexibility and scalability, DOTS servers SHOULD be able to 418 redirect DOTS clients to another DOTS server at any time. DOTS 419 clients MUST NOT assume the redirection target DOTS server shares 420 security state with the redirecting DOTS server. DOTS clients are 421 free to attempt abbreviated security negotiation methods supported 422 by the protocol, such as DTLS session resumption, but MUST be 423 prepared to negotiate new security state with the redirection 424 target DOTS server. The authentication domain of the redirection 425 target DOTS server MUST be the same as the authentication domain 426 of the redirecting DOTS server. 428 Due to the increased likelihood of packet loss caused by link 429 congestion during an attack, DOTS servers SHOULD NOT redirect 430 while mitigation is enabled during an active attack against a 431 target in the DOTS client's domain. 433 SIG-006 Mitigation Requests and Status: Authorized DOTS clients MUST 434 be able to request scoped mitigation from DOTS servers. DOTS 435 servers MUST send status to the DOTS clients about mitigation 436 requests. If a DOTS server rejects an authorized request for 437 mitigation, the DOTS server MUST include a reason for the 438 rejection in the status message sent to the client. 440 Due to the higher likelihood of packet loss during a DDoS attack, 441 DOTS servers MUST regularly send mitigation status to authorized 442 DOTS clients which have requested and been granted mitigation, 443 regardless of client requests for mitigation status. 445 When DOTS client-requested mitigation is active, DOTS server 446 status messages MUST include the following mitigation metrics: 448 * Total number of packets blocked by the mitigation 450 * Current number of packets per second blocked 452 * Total number of bytes blocked 454 * Current number of bytes per second blocked 456 DOTS clients MAY take these metrics into account when determining 457 whether to ask the DOTS server to cease mitigation. 459 A DOTS client MAY withdraw a mitigation request at any time, 460 regardless of whether mitigation is currently active. The DOTS 461 server MUST immediately acknowledge a DOTS client's request to 462 stop mitigation. 464 To protect against route or DNS flapping caused by a client 465 rapidly toggling mitigation, and to dampen the effect of 466 oscillating attacks, DOTS servers MAY allow mitigation to continue 467 for a limited period after acknowledging a DOTS client's 468 withdrawal of a mitigation request. During this period, DOTS 469 server status messages SHOULD indicate that mitigation is active 470 but terminating. DOTS clients MAY reverse the mitigation 471 termination during this active-but-terminating period with a new 472 mitigation request for the same scope. The DOTS server MUST treat 473 this request as a mitigation lifetime extension (see SIG-007 474 below). 476 The initial active-but-terminating period is implementation- and 477 deployment- specific, but SHOULD be sufficiently long to absorb 478 latency incurred by route propagation. If a DOTS client refreshes 479 the mitigation before the active-but-terminating period elapses, 480 the DOTS server MAY increase the active-but-terminating period up 481 to a maximum of 300 seconds (5 minutes). After the active-but- 482 terminating period elapses, the DOTS server MUST treat the 483 mitigation as terminated, as the DOTS client is no longer 484 responsible for the mitigation. 486 SIG-007 Mitigation Lifetime: DOTS servers MUST support mitigations 487 for a negotiated time interval, and MUST terminate a mitigation 488 when the lifetime elapses. DOTS servers also MUST support renewal 489 of mitigation lifetimes in mitigation requests from DOTS clients, 490 allowing clients to extend mitigation as necessary for the 491 duration of an attack. 493 DOTS servers MUST treat a mitigation terminated due to lifetime 494 expiration exactly as if the DOTS client originating the 495 mitigation had asked to end the mitigation, including the active- 496 but-terminating period, as described above in SIG-005. 498 DOTS clients MUST include a mitigation lifetime in all mitigation 499 requests. 501 DOTS servers SHOULD support indefinite mitigation lifetimes, 502 enabling architectures in which the mitigator is always in the 503 traffic path to the resources for which the DOTS client is 504 requesting protection. DOTS clients MUST be prepared to not be 505 granted mitigations with indefinite lifetimes. DOTS servers MAY 506 refuse mitigations with indefinite lifetimes, for policy reasons. 507 The reasons themselves are out of scope. If the DOTS server does 508 not grant a mitigation request with an indefinite mitigation 509 lifetime, it MUST set the lifetime to a value that is configured 510 locally. That value MUST be returned in a reply to the requesting 511 DOTS client. 513 SIG-008 Mitigation Scope: DOTS clients MUST indicate desired 514 mitigation scope. The scope type will vary depending on the 515 resources requiring mitigation. All DOTS agent implementations 516 MUST support the following required scope types: 518 * IPv4 prefixes [RFC4632] 520 * IPv6 prefixes [RFC4291][RFC5952] 522 * Domain names [RFC1035] 524 The following mitigation scope types are OPTIONAL: 526 * Uniform Resource Identifiers [RFC3986] 528 DOTS servers MUST be able to resolve domain names and (when 529 supported) URIs. How name resolution is managed on the DOTS 530 server is implementation-specific. 532 DOTS agents MUST support mitigation scope aliases, allowing DOTS 533 clients and servers to refer to collections of protected resources 534 by an opaque identifier created through the data channel, direct 535 configuration, or other means. Domain name and URI mitigation 536 scopes may be thought of as a form of scope alias, in which the 537 addresses to which the domain name or URI resolve represent the 538 full scope of the mitigation. 540 If there is additional information available narrowing the scope 541 of any requested attack response, such as targeted port range, 542 protocol, or service, DOTS clients SHOULD include that information 543 in client mitigation requests. DOTS clients MAY also include 544 additional attack details. DOTS servers MAY ignore such 545 supplemental information when enabling countermeasures on the 546 mitigator. 548 As an active attack evolves, DOTS clients MUST be able to adjust 549 as necessary the scope of requested mitigation by refining the 550 scope of resources requiring mitigation. 552 A DOTS client may obtain the mitigation scope through direct 553 provisioning or through implementation-specific methods of 554 discovery. DOTS clients MUST support at least one mechanism to 555 obtain mitigation scope. 557 SIG-009 Mitigation Efficacy: When a mitigation request is active, 558 DOTS clients MUST transmit a metric of perceived mitigation 559 efficacy to the DOTS server. DOTS servers MAY use the efficacy 560 metric to adjust countermeasures activated on a mitigator on 561 behalf of a DOTS client. 563 SIG-010 Conflict Detection and Notification: Multiple DOTS clients 564 controlled by a single administrative entity may send conflicting 565 mitigation requests as a result of misconfiguration, operator 566 error, or compromised DOTS clients. DOTS servers in the same 567 administrative domain attempting to honor conflicting requests may 568 flap network route or DNS information, degrading the networks 569 attempting to participate in attack response with the DOTS 570 clients. DOTS servers in a single administrative domain SHALL 571 detect such conflicting requests, and SHALL notify the DOTS 572 clients in conflict. The notification MUST indicate the nature 573 and scope of the conflict, for example, the overlapping prefix 574 range in a conflicting mitigation request. 576 SIG-011 Network Address Translator Traversal: DOTS clients may be 577 deployed behind a Network Address Translator (NAT), and need to 578 communicate with DOTS servers through the NAT. DOTS protocols 579 MUST therefore be capable of traversing NATs. 581 If UDP is used as the transport for the DOTS signal channel, all 582 considerations in "Middlebox Traversal Guidelines" in [RFC8085] 583 apply to DOTS. Regardless of transport, DOTS protocols MUST 584 follow established best common practices established in BCP 127 585 for NAT traversal [RFC4787][RFC6888][RFC7857]. 587 2.3. Data Channel Requirements 589 The data channel is intended to be used for bulk data exchanges 590 between DOTS agents. Unlike the signal channel, the data channel is 591 not expected to be constructed to deal with attack conditions. As 592 the primary function of the data channel is data exchange, a reliable 593 transport is required in order for DOTS agents to detect data 594 delivery success or failure. 596 The data channel provides a protocol for DOTS configuration, 597 management. For example, a DOTS client may submit to a DOTS server a 598 collection of prefixes it wants to refer to by alias when requesting 599 mitigation, to which the server would respond with a success status 600 and the new prefix group alias, or an error status and message in the 601 event the DOTS client's data channel request failed. 603 DATA-001 Reliable transport: Messages sent over the data channel 604 MUST be delivered reliably, in order sent. 606 DATA-002 Data privacy and integrity: Transmissions over the data 607 channel are likely to contain operationally or privacy-sensitive 608 information or instructions from the remote DOTS agent. Theft, 609 modification, or replay of data channel transmissions could lead 610 to information leaks or malicious transactions on behalf of the 611 sending agent (see Section 4 below). Consequently data sent over 612 the data channel MUST be encrypted using a secure transport (like 613 TLS). DOTS servers MUST enable means to prevent leaking 614 operationally or privacy-sensitive data. Although administrative 615 entities participating in DOTS may detail what data may be 616 revealed to third-party DOTS agents, such considerations are not 617 in scope for this document. 619 DATA-003 Resource Configuration: To help meet the general and signal 620 channel requirements in Section 2.1 and Section 2.2, DOTS server 621 implementations MUST provide an interface to configure resource 622 identifiers, as described in SIG-008. DOTS server implementations 623 MAY expose additional configurability. Additional configurability 624 is implementation-specific. 626 DATA-004 Policy management: DOTS servers MUST provide methods for 627 DOTS clients to manage drop- and accept-lists of traffic destined 628 for resources belonging to a client. 630 For example, a DOTS client should be able to create a drop- or 631 accept-list entry, retrieve a list of current entries from either 632 list, update the content of either list, and delete entries as 633 necessary. 635 How a DOTS server authorizes DOTS client management of drop- and 636 accept-list entries is implementation-specific. 638 2.4. Security Requirements 640 DOTS must operate within a particularly strict security context, as 641 an insufficiently protected signal or data channel may be subject to 642 abuse, enabling or supplementing the very attacks DOTS purports to 643 mitigate. 645 SEC-001 Peer Mutual Authentication: DOTS agents MUST authenticate 646 each other before a DOTS signal or data channel is considered 647 valid. The method of authentication is not specified in this 648 document, but should follow current industry best practices with 649 respect to any cryptographic mechanisms to authenticate the remote 650 peer. 652 SEC-002 Message Confidentiality, Integrity and Authenticity: DOTS 653 protocols MUST take steps to protect the confidentiality, 654 integrity and authenticity of messages sent between client and 655 server. While specific transport- and message-level security 656 options are not specified, the protocols MUST follow current 657 industry best practices for encryption and message authentication. 658 Client-domain DOTS gateways are more trusted than DOTS clients, 659 while server-domain DOTS gateways and DOTS servers share the same 660 level of trust. A security mechanism at the network layer (e.g., 661 TLS) is thus adequate to provide hop-by-hop security. In other 662 words, end-to-end security is not required for DOTS protocols. 664 In order for DOTS protocols to remain secure despite advancements 665 in cryptanalysis and traffic analysis, DOTS agents MUST support 666 secure negotiation of the terms and mechanisms of protocol 667 security, subject to the interoperability and signal message size 668 requirements in Section 2.2. 670 While the interfaces between downstream DOTS server and upstream 671 DOTS client within a DOTS gateway are implementation-specific, 672 those interfaces nevertheless MUST provide security equivalent to 673 that of the signal channels bridged by gateways in the signaling 674 path. For example, when a DOTS gateway consisting of a DOTS 675 server and DOTS client is running on the same logical device, the 676 two DOTS agents could be implemented within the same process 677 security boundary. 679 SEC-003 Message Replay Protection: To prevent a passive attacker 680 from capturing and replaying old messages, and thereby potentially 681 disrupting or influencing the network policy of the receiving DOTS 682 agent's domain, DOTS protocols MUST provide a method for replay 683 detection and prevention. 685 Within the signal channel, messages MUST be uniquely identified 686 such that replayed or duplicated messages can be detected and 687 discarded. Unique mitigation requests MUST be processed at most 688 once. 690 SEC-004 Authorization: DOTS servers MUST authorize all messages from 691 DOTS clients which pertain to mitigation, configuration, 692 filtering, or status. 694 DOTS servers MUST reject mitigation requests with scopes which the 695 DOTS client is not authorized to manage. 697 Likewise, DOTS servers MUST refuse to allow creation, modification 698 or deletion of scope aliases and drop-/accept-lists when the DOTS 699 client is unauthorized. 701 The modes of authorization are implementation-specific. 703 2.5. Data Model Requirements 705 A well-structured DOTS data model is critical to the development of 706 successful DOTS protocols. 708 DM-001 Structure: The data model structure for the DOTS protocol MAY 709 be described by a single module, or be divided into related 710 collections of hierarchical modules and sub-modules. If the data 711 model structure is split across modules, those distinct modules 712 MUST allow references to describe the overall data model's 713 structural dependencies. 715 DM-002 Versioning: To ensure interoperability between DOTS protocol 716 implementations, data models MUST be versioned. How the protocols 717 represent data model versions is not defined in this document. 719 DM-003 Mitigation Status Representation: The data model MUST provide 720 the ability to represent a request for mitigation and the 721 withdrawal of such a request. The data model MUST also support a 722 representation of currently requested mitigation status, including 723 failures and their causes. 725 DM-004 Mitigation Scope Representation: The data model MUST support 726 representation of a requested mitigation's scope. As mitigation 727 scope may be represented in several different ways, per SIG-008 728 above, the data model MUST include extensible representation of 729 mitigation scope. 731 DM-005 Mitigation Lifetime Representation: The data model MUST 732 support representation of a mitigation request's lifetime, 733 including mitigations with no specified end time. 735 DM-006 Mitigation Efficacy Representation: The data model MUST 736 support representation of a DOTS client's understanding of the 737 efficacy of a mitigation enabled through a mitigation request. 739 DM-007 Acceptable Signal Loss Representation: The data model MUST be 740 able to represent the DOTS agent's preference for acceptable 741 signal loss when establishing a signal channel. Measurements of 742 loss might include, but are not restricted to, number of 743 consecutive missed heartbeat messages, retransmission count, or 744 request timeouts. 746 DM-008 Heartbeat Interval Representation: The data model MUST be 747 able to represent the DOTS agent's preferred heartbeat interval, 748 which the client may include when establishing the signal channel, 749 as described in SIG-003. 751 DM-009 Relationship to Transport: The DOTS data model MUST NOT make 752 any assumptions about specific characteristics of any given 753 transport into the data model, but instead, represent the fields 754 in the model explicitly. 756 3. Congestion Control Considerations 758 3.1. Signal Channel 760 As part of a protocol expected to operate over links affected by DDoS 761 attack traffic, the DOTS signal channel MUST NOT contribute 762 significantly to link congestion. To meet the signal channel 763 requirements above, DOTS signal channel implementations SHOULD 764 support connectionless transports. However, some connectionless 765 transports when deployed naively can be a source of network 766 congestion, as discussed in [RFC8085]. Signal channel 767 implementations using such connectionless transports, such as UDP, 768 therefore MUST include a congestion control mechanism. 770 Signal channel implementations using a IETF standard congestion- 771 controlled transport protocol (like TCP) may rely on built-in 772 transport congestion control support. 774 3.2. Data Channel 776 As specified in DATA-001, the data channel requires reliable, in- 777 order message delivery. Data channel implementations using a IETF 778 standard congestion-controlled transport protocol may rely on the 779 transport implementation's built-in congestion control mechanisms. 781 4. Security Considerations 783 This document informs future protocols under development, and so does 784 not have security considerations of its own. However, operators 785 should be aware of potential risks involved in deploying DOTS. DOTS 786 agent impersonation and signal blocking are discussed here. 787 Additional DOTS security considerations may be found in 788 [I-D.ietf-dots-architecture] and DOTS protocol documents. 790 Impersonation of either a DOTS server or a DOTS client could have 791 catastrophic impact on operations in either domain. If an attacker 792 has the ability to impersonate a DOTS client, that attacker can 793 affect policy on the network path to the DOTS client's domain, up to 794 and including instantiation of drop-lists blocking all inbound 795 traffic to networks for which the DOTS client is authorized to 796 request mitigation. 798 Similarly, an impersonated DOTS server may be able to act as a sort 799 of malicious DOTS gateway, intercepting requests from the downstream 800 DOTS client, and modifying them before transmission to the DOTS 801 server to inflict the desired impact on traffic to or from the DOTS 802 client's domain. Among other things, this malicious DOTS gateway 803 might receive and discard mitigation requests from the DOTS client, 804 ensuring no requested mitigation is ever applied. 806 To detect misuse, as detailed in Section 2.4, DOTS implementations 807 require mutual authentication of DOTS agents in order to make agent 808 impersonation more difficult. However, impersonation may still be 809 possible as a result of credential theft, implementation flaws, or 810 compromise of DOTS agents. 812 To detect compromised DOTS agents, DOTS operators should carefully 813 monitor and audit DOTS agents to detect misbehavior and to deter 814 misuse, while employing current secure network communications best 815 practices to reduce attack surface. 817 Blocking communication between DOTS agents has the potential to 818 disrupt the core function of DOTS, which is to request mitigation of 819 active or expected DDoS attacks. The DOTS signal channel is expected 820 to operate over congested inbound links, and, as described in 821 Section 2.2, the signal channel protocol must be designed for minimal 822 data transfer to reduce the incidence of signal loss. 824 5. IANA Considerations 826 This document does not require any IANA action. 828 6. Contributors 830 Mohamed Boucadair 831 Orange 833 mohamed.boucadair@orange.com 835 Flemming Andreasen 836 Cisco Systems, Inc. 838 fandreas@cisco.com 840 Dave Dolson 841 Sandvine 843 ddolson@sandvine.com 845 7. Acknowledgments 847 Thanks to Roman Danyliw, Matt Richardson, Joe Touch, Scott Bradner, 848 Robert Sparks, Brian Weis, Benjamin Kaduk and Jon Shallow for careful 849 reading and feedback. 851 8. References 853 8.1. Normative References 855 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 856 DOI 10.17487/RFC0768, August 1980, 857 . 859 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 860 DOI 10.17487/RFC0791, September 1981, 861 . 863 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 864 RFC 793, DOI 10.17487/RFC0793, September 1981, 865 . 867 [RFC1035] Mockapetris, P., "Domain names - implementation and 868 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 869 November 1987, . 871 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 872 Communication Layers", STD 3, RFC 1122, 873 DOI 10.17487/RFC1122, October 1989, 874 . 876 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 877 Requirement Levels", BCP 14, RFC 2119, 878 DOI 10.17487/RFC2119, March 1997, 879 . 881 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 882 Resource Identifier (URI): Generic Syntax", STD 66, 883 RFC 3986, DOI 10.17487/RFC3986, January 2005, 884 . 886 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 887 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 888 2006, . 890 [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing 891 (CIDR): The Internet Address Assignment and Aggregation 892 Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August 893 2006, . 895 [RFC4787] Audet, F., Ed. and C. Jennings, "Network Address 896 Translation (NAT) Behavioral Requirements for Unicast 897 UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January 898 2007, . 900 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 901 Address Text Representation", RFC 5952, 902 DOI 10.17487/RFC5952, August 2010, 903 . 905 [RFC6888] Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa, 906 A., and H. Ashida, "Common Requirements for Carrier-Grade 907 NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888, 908 April 2013, . 910 [RFC7857] Penno, R., Perreault, S., Boucadair, M., Ed., Sivakumar, 911 S., and K. Naito, "Updates to Network Address Translation 912 (NAT) Behavioral Requirements", BCP 127, RFC 7857, 913 DOI 10.17487/RFC7857, April 2016, 914 . 916 [RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage 917 Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, 918 March 2017, . 920 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 921 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 922 May 2017, . 924 8.2. Informative References 926 [I-D.ietf-dots-architecture] 927 Mortensen, A., Andreasen, F., K, R., Teague, N., Compton, 928 R., and c. christopher_gray3@cable.comcast.com, 929 "Distributed-Denial-of-Service Open Threat Signaling 930 (DOTS) Architecture", draft-ietf-dots-architecture-10 931 (work in progress), December 2018. 933 [I-D.ietf-dots-use-cases] 934 Dobbins, R., Migault, D., Fouant, S., Moskowitz, R., 935 Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS 936 Open Threat Signaling", draft-ietf-dots-use-cases-17 (work 937 in progress), January 2019. 939 [I-D.ietf-intarea-frag-fragile] 940 Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 941 and F. Gont, "IP Fragmentation Considered Fragile", draft- 942 ietf-intarea-frag-fragile-08 (work in progress), January 943 2019. 945 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 946 A., Peterson, J., Sparks, R., Handley, M., and E. 947 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 948 DOI 10.17487/RFC3261, June 2002, 949 . 951 [RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session 952 Initiation Protocol (SIP) Back-to-Back User Agents", 953 RFC 7092, DOI 10.17487/RFC7092, December 2013, 954 . 956 [RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet 957 Denial-of-Service Considerations", RFC 4732, 958 DOI 10.17487/RFC4732, December 2006, 959 . 961 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", 962 FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, 963 . 965 Authors' Addresses 967 Andrew Mortensen 968 Arbor Networks 969 2727 S. State St 970 Ann Arbor, MI 48104 971 United States 973 Email: andrewmortensen@gmail.com 975 Tirumaleswar Reddy 976 McAfee 977 Embassy Golf Link Business Park 978 Bangalore, Karnataka 560071 979 India 981 Email: TirumaleswarReddy_Konda@McAfee.com 983 Robert Moskowitz 984 Huawei 985 Oak Park, MI 42837 986 United States 988 Email: rgm@htt-consult.com