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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** Obsolete normative reference: RFC 793 (Obsoleted by RFC 9293) == Outdated reference: A later version (-18) exists of draft-ietf-dots-architecture-05 == Outdated reference: A later version (-25) exists of draft-ietf-dots-use-cases-09 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 DOTS A. Mortensen 3 Internet-Draft Arbor Networks 4 Intended status: Informational R. Moskowitz 5 Expires: August 12, 2018 Huawei 6 T. Reddy 7 McAfee 8 February 08, 2018 10 Distributed Denial of Service (DDoS) Open Threat Signaling Requirements 11 draft-ietf-dots-requirements-14 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 12, 2018. 36 Copyright Notice 38 Copyright (c) 2018 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (https://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 1.1. Context and Motivation . . . . . . . . . . . . . . . . . 2 55 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 56 2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5 57 2.1. General Requirements . . . . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . 14 62 3. Congestion Control Considerations . . . . . . . . . . . . . . 15 63 3.1. Signal Channel . . . . . . . . . . . . . . . . . . . . . 15 64 3.2. Data Channel . . . . . . . . . . . . . . . . . . . . . . 16 65 4. Security Considerations . . . . . . . . . . . . . . . . . . . 16 66 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 67 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 17 68 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 69 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 70 8.1. Normative References . . . . . . . . . . . . . . . . . . 17 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 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 [RFC2119]. 119 This document adopts the following terms: 121 DDoS: A distributed denial-of-service attack, in which traffic 122 originating from multiple sources is directed at a target on a 123 network. DDoS attacks are intended to cause a negative impact on 124 the availability and/or other functionality of an attack target. 125 Denial-of-service considerations are discussed in detail in 126 [RFC4732]. 128 DDoS attack target: A network connected entity with a finite set of 129 resources, such as network bandwidth, memory or CPU, that is the 130 target of a DDoS attack. Potential targets include (but are not 131 limited to) network elements, network links, servers, and 132 services. 134 DDoS attack telemetry: Collected measurements and behavioral 135 characteristics defining the nature of a DDoS attack. 137 Countermeasure: An action or set of actions focused on recognizing 138 and filtering out specific types of DDoS attack traffic while 139 passing legitimate traffic to the attack target. Distinct 140 countermeasures can be layered to defend against attacks combining 141 multiple DDoS attack types. 143 Mitigation: A set of countermeasures enforced against traffic 144 destined for the target or targets of a detected or reported DDoS 145 attack, where countermeasure enforcement is managed by an entity 146 in the network path between attack sources and the attack target. 147 Mitigation methodology is out of scope for this document. 149 Mitigator: An entity, typically a network element, capable of 150 performing mitigation of a detected or reported DDoS attack. The 151 means by which this entity performs these mitigations and how they 152 are requested of it are out of scope. The mitigator and DOTS 153 server receiving a mitigation request are assumed to belong to the 154 same administrative entity. 156 DOTS client: A DOTS-aware software module responsible for requesting 157 attack response coordination with other DOTS-aware elements. 159 DOTS server: A DOTS-aware software module handling and responding to 160 messages from DOTS clients. The DOTS server enables mitigation on 161 behalf of the DOTS client, if requested, by communicating the DOTS 162 client's request to the mitigator and returning selected mitigator 163 feedback to the requesting DOTS client. 165 DOTS agent: Any DOTS-aware software module capable of participating 166 in a DOTS signal or data channel. It can be a DOTS client, DOTS 167 server, or, as a logical agent, a DOTS gateway. 169 DOTS gateway: A DOTS-aware software module resulting from the 170 logical concatenation of the functionality of a DOTS server and a 171 DOTS client into a single DOTS agent. This functionality is 172 analogous to a Session Initiation Protocol (SIP) [RFC3261] Back- 173 to-Back User Agent (B2BUA) [RFC7092]. A DOTS gateway has a 174 client-facing side, which behaves as a DOTS server for downstream 175 clients, and a server-facing side, which performs the role of DOTS 176 client for upstream DOTS servers. Client-domain DOTS gateways are 177 DOTS gateways that are in the DOTS client's domain, while server- 178 domain DOTS gateways denote DOTS gateways that are in the DOTS 179 server's domain. DOTS gateways are described further in 180 [I-D.ietf-dots-architecture]. 182 Signal channel: A bidirectional, mutually authenticated 183 communication channel between DOTS agents that is resilient even 184 in conditions leading to severe packet loss, such as a volumetric 185 DDoS attack causing network congestion. 187 DOTS signal: A concise authenticated status/control message 188 transmitted over the signal channel between DOTS agents, used to 189 indicate the client's need for mitigation, as well as to convey 190 the status of any requested mitigation. 192 Heartbeat: A message transmitted between DOTS agents over the signal 193 channel, used as a keep-alive and to measure peer health. 195 Data channel: A bidirectional, mutually authentication 196 communincation channel between two DOTS agents used for infrequent 197 but reliable bulk exchange of data not easily or appropriately 198 communicated through the signal channel under attack conditions. 200 Filter: A specification of a matching network traffic flow or set of 201 flows. The filter will typically have a policy associated with 202 it, e.g., rate-limiting or discarding matching traffic [RFC4949]. 204 Blacklist: A list of filters indicating sources from which traffic 205 should be blocked, regardless of traffic content. 207 Whitelist: A list of filters indicating sources from which traffic 208 should always be allowed, regardless of contradictory data gleaned 209 in a detected attack. 211 Multi-homed DOTS client: A DOTS client exchanging messages with 212 multiple DOTS servers, each in a separate administrative domain. 214 2. Requirements 216 This section describes the required features and characteristics of 217 the DOTS protocols. 219 The DOTS protocols enable and manage mitigation on behalf of a 220 network domain or resource which is or may become the focus of a DDoS 221 attack. An active DDoS attack against the entity controlling the 222 DOTS client need not be present before establishing a communication 223 channel between DOTS agents. Indeed, establishing a relationship 224 with peer DOTS agents during normal network conditions provides the 225 foundation for more rapid attack response against future attacks, as 226 all interactions setting up DOTS, including any business or service 227 level agreements, are already complete. Reachability information of 228 peer DOTS agents is provisioned to a DOTS client using a variety of 229 manual or dynamic methods. Once a relationship between DOTS agents 230 is established, regular communication between DOTS clients and 231 servers enables a common understanding of the DOTS agents' health and 232 activity. 234 The DOTS protocol must at a minimum make it possible for a DOTS 235 client to request aid mounting a defense, coordinated by a DOTS 236 server, against a suspected attack, signaling within or between 237 domains as requested by local operators. DOTS clients should 238 similarly be able to withdraw aid requests. DOTS requires no 239 justification from DOTS clients for requests for help, nor do DOTS 240 clients need to justify withdrawing help requests: the decision is 241 local to the DOTS clients' domain. Multi-homed DOTS clients must be 242 able to select the appropriate DOTS server(s) to which a mitigation 243 request is to be sent. The method for selecting the appropriate DOTS 244 server in a multi-homed environment is out of scope. 246 DOTS protocol implementations face competing operational goals when 247 maintaining this bidirectional communication stream. On the one 248 hand, DOTS must include protections ensuring message confidentiality, 249 integrity and authenticity to keep the protocols from becoming 250 additional vectors for the very attacks it is meant to help fight 251 off. On the other hand, the protocol must be resilient under 252 extremely hostile network conditions, providing continued contact 253 between DOTS agents even as attack traffic saturates the link. Such 254 resiliency may be developed several ways, but characteristics such as 255 small message size, asynchronous, redundant message delivery and 256 minimal connection overhead (when possible given local network 257 policy) will tend to contribute to the robustness demanded by a 258 viable DOTS protocol. Operators of peer DOTS-enabled domains may 259 enable quality- or class-of-service traffic tagging to increase the 260 probability of successful DOTS signal delivery, but DOTS does not 261 require such policies be in place, and should be viable in their 262 absence. 264 The DOTS server and client must also have some standardized method of 265 defining the scope of any mitigation, as well as managing other 266 mitigation-related configuration. 268 Finally, DOTS should be sufficiently extensible to meet future needs 269 in coordinated attack defense, although this consideration is 270 necessarily superseded by the other operational requirements. 272 2.1. General Requirements 274 GEN-001 Extensibility: Protocols and data models developed as part 275 of DOTS MUST be extensible in order to keep DOTS adaptable to 276 operational and proprietary DDoS defenses. Future extensions MUST 277 be backward compatible. DOTS protocols MUST use a version number 278 system to distinguish protocol revisions. Implementations of 279 older protocol versions SHOULD ignore information added to DOTS 280 messages as part of newer protocol versions. 282 GEN-002 Resilience and Robustness: The signaling protocol MUST be 283 designed to maximize the probability of signal delivery even under 284 the severely constrained network conditions caused by particular 285 attack traffic. The protocol MUST be resilient, that is, continue 286 operating despite message loss and out-of-order or redundant 287 message delivery. In support of signaling protocol robustness, 288 DOTS signals SHOULD be conveyed over a transport not susceptible 289 to Head of Line Blocking. 291 GEN-003 Bulk Data Exchange: Infrequent bulk data exchange between 292 DOTS agents can also significantly augment attack response 293 coordination, permitting such tasks as population of black- or 294 white-listed source addresses; address or prefix group aliasing; 295 exchange of incident reports; and other hinting or configuration 296 supplementing attack response. 298 As the resilience requirements for the DOTS signal channel mandate 299 small signal message size, a separate, secure data channel 300 utilizing a reliable transport protocol MUST be used for bulk data 301 exchange. 303 GEN-004 Mitigation Hinting: DOTS clients may have access to attack 304 details which can be used to inform mitigation techniques. 305 Example attack details might include locally collected 306 fingerprints for an on-going attack, or anticipated or active 307 attack focal points based on other threat intelligence. DOTS 308 clients MAY send mitigation hints derived from attack details to 309 DOTS servers, in the full understanding that the DOTS server MAY 310 ignore mitigation hints. Mitigation hints MAY be transmitted 311 across either signal or data channel. DOTS server handling of 312 mitigation hints is implementation-specific. 314 GEN-005 Loop Handling: In certain scenarios, typically involving 315 misconfiguration of DNS or routing policy, it may be possible for 316 communication between DOTS agents to loop. Signal and data 317 channel implementations should be prepared to detect and terminate 318 such loops to prevent service disruption. 320 2.2. Signal Channel Requirements 322 SIG-001 Use of Common Transport Protocols: DOTS MUST operate over 323 common widely deployed and standardized transport protocols. 324 While connectionless transport such as the User Datagram Protocol 325 (UDP) [RFC0768] SHOULD be used for the signal channel, the 326 Transmission Control Protocol (TCP) [RFC0793] MAY be used if 327 necessary due to network policy or middlebox capabilities or 328 configurations. 330 SIG-002 Sub-MTU Message Size: To avoid message fragmentation and the 331 consequently decreased probability of message delivery over a 332 congested link, signaling protocol message size MUST be kept under 333 signaling Path Maximum Transmission Unit (PMTU), including the 334 byte overhead of any encapsulation, transport headers, and 335 transport- or message-level security. 337 DOTS agents SHOULD attempt to learn the PMTU through mechanisms 338 such as Path MTU Discovery [RFC1191] or Packetization Layer Path 339 MTU Discovery [RFC4821]. If the PMTU cannot be discovered, DOTS 340 agents SHOULD assume a PMTU of 1280 bytes. If IPv4 support on 341 legacy or otherwise unusual networks is a consideration and PMTU 342 is unknown, DOTS implementations MAY rely on a PMTU of 576 bytes, 343 as discussed in [RFC0791] and [RFC1122]. 345 SIG-003 Bidirectionality: To support peer health detection, to 346 maintain an active signal channel, and increase the probability of 347 signal delivery during an attack, the signal channel MUST be 348 bidirectional, with client and server transmitting signals to each 349 other at regular intervals, regardless of any client request for 350 mitigation. Unidirectional messages MUST be supported within the 351 bidirectional signal channel to allow for unsolicited message 352 delivery, enabling asynchronous notifications between DOTS agents. 354 SIG-004 Channel Health Monitoring: DOTS agents MUST support exchange 355 of heartbeat messages over the signal channel to monitor channel 356 health. Peer DOTS agents SHOULD regularly send heartbeats to each 357 other while a mitigation request is active. The heartbeat 358 interval during active mitigation could be negotiable, but SHOULD 359 be frequent enough to maintain any on-path NAT or Firewall 360 bindings during mitigation. 362 To support scenarios in which loss of heartbeat is used to trigger 363 mitigation, and to keep the channel active, DOTS clients MAY 364 solicit heartbeat exchanges after successful mutual 365 authentication. When DOTS agents are exchanging heartbeats and no 366 mitigation request is active, either agent MAY request changes to 367 the heartbeat rate. For example, a DOTS server might want to 368 reduce heartbeat frequency or cease heartbeat exchanges when an 369 active DOTS client has not requested mitigation, in order to 370 control load. 372 Following mutual authentication, a signal channel MUST be 373 considered active until a DOTS agent explicitly ends the session, 374 or either DOTS agent fails to receive heartbeats from the other 375 after a mutually agreed upon retransmission procedure has been 376 exhausted. Because heartbeat loss is much more likely during 377 volumetric attack, DOTS agents SHOULD avoid signal channel 378 termination when mitigation is active and heartbeats are not 379 received by either DOTS agent for an extended period. In such 380 circumstances, DOTS clients MAY attempt to reestablish the signal 381 channel, but SHOULD continue to send heartbeats so that the DOTS 382 server knows the session is still alive. DOTS servers are assumed 383 to have the ability to monitor the attack, using feedback from the 384 mitigator and other available sources, and MAY use the absence of 385 attack traffic and lack of client heartbeats as an indication the 386 signal channel is defunct. 388 SIG-005 Channel Redirection: In order to increase DOTS operational 389 flexibility and scalability, DOTS servers SHOULD be able to 390 redirect DOTS clients to another DOTS server at any time. DOTS 391 clients MUST NOT assume the redirection target DOTS server shares 392 security state with the redirecting DOTS server. DOTS clients are 393 free to attempt abbreviated security negotiation methods supported 394 by the protocol, such as DTLS session resumption, but MUST be 395 prepared to negotiate new security state with the redirection 396 target DOTS server. 398 Due to the increased likelihood of packet loss caused by link 399 congestion during an attack, DOTS servers SHOULD NOT redirect 400 while mitigation is enabled during an active attack against a 401 target in the DOTS client's domain. 403 SIG-006 Mitigation Requests and Status: Authorized DOTS clients MUST 404 be able to request scoped mitigation from DOTS servers. DOTS 405 servers MUST send status to the DOTS clients about mitigation 406 requests. If a DOTS server rejects an authorized request for 407 mitigation, the DOTS server MUST include a reason for the 408 rejection in the status message sent to the client. 410 Due to the higher likelihood of packet loss during a DDoS attack, 411 DOTS servers SHOULD regularly send mitigation status to authorized 412 DOTS clients which have requested and been granted mitigation, 413 regardless of client requests for mitigation status. 415 When DOTS client-requested mitigation is active, DOTS server 416 status messages SHOULD include the following mitigation metrics: 418 * Total number of packets blocked by the mitigation 420 * Current number of packets per second blocked 422 * Total number of bytes blocked 424 * Current number of bytes per second blocked 426 DOTS clients MAY take these metrics into account when determining 427 whether to ask the DOTS server to cease mitigation. 429 A DOTS client MAY withdraw a mitigation request at any time, 430 regardless of whether mitigation is currently active. The DOTS 431 server MUST immediately acknowledge a DOTS client's request to 432 stop mitigation. 434 To protect against route or DNS flapping caused by a client 435 rapidly toggling mitigation, and to dampen the effect of 436 oscillating attacks, DOTS servers MAY allow mitigation to continue 437 for a limited period after acknowledging a DOTS client's 438 withdrawal of a mitigation request. During this period, DOTS 439 server status messages SHOULD indicate that mitigation is active 440 but terminating. 442 The initial active-but-terminating period is implementation- and 443 deployment- specific, but SHOULD be sufficiently long to absorb 444 latency incurred by route propagation. If the client requests 445 mitigation again before the initial active-but-terminating period 446 elapses, the DOTS server MAY exponentially increase the active- 447 but-terminating period up to a maximum of 300 seconds (5 minutes). 448 After the active-but-terminating period elapses, the DOTS server 449 MUST treat the mitigation as terminated, as the DOTS client is no 450 longer responsible for the mitigation. 452 SIG-007 Mitigation Lifetime: DOTS servers MUST support mitigations 453 for a negotiated time interval, and MUST terminate a mitigation 454 when the lifetime elapses. DOTS servers also MUST support renewal 455 of mitigation lifetimes in mitigation requests from DOTS clients, 456 allowing clients to extend mitigation as necessary for the 457 duration of an attack. 459 DOTS servers MUST treat a mitigation terminated due to lifetime 460 expiration exactly as if the DOTS client originating the 461 mitigation had asked to end the mitigation, including the active- 462 but-terminating period, as described above in SIG-005. 464 DOTS clients MUST include a mitigation lifetime in all mitigation 465 requests. 467 DOTS servers SHOULD support indefinite mitigation lifetimes, 468 enabling architectures in which the mitigator is always in the 469 traffic path to the resources for which the DOTS client is 470 requesting protection. DOTS clients MUST be prepared to not be 471 granted mitigations with indefinite lifetimes. DOTS servers MAY 472 refuse mitigations with indefinite lifetimes, for policy reasons. 473 The reasons themselves are out of scope. If the DOTS server does 474 not grant a mitigation request with an indefinite mitigation 475 lifetime, it MUST set the lifetime to a value that is configured 476 locally. That value MUST be returned in a reply to the requesting 477 DOTS client. 479 SIG-008 Mitigation Scope: DOTS clients MUST indicate desired 480 mitigation scope. The scope type will vary depending on the 481 resources requiring mitigation. All DOTS agent implementations 482 MUST support the following required scope types: 484 * IPv4 prefixes in CIDR notation [RFC4632] 486 * IPv6 prefixes [RFC4291][RFC5952] 488 * Domain names [RFC1035] 490 The following mitigation scope types are OPTIONAL: 492 * Uniform Resource Identifiers [RFC3986] 494 DOTS servers MUST be able to resolve domain names and (when 495 supported) URIs. How name resolution is managed on the DOTS 496 server is implementation-specific. 498 DOTS agents MUST support mitigation scope aliases, allowing DOTS 499 clients and servers to refer to collections of protected resources 500 by an opaque identifier created through the data channel, direct 501 configuration, or other means. Domain name and URI mitigation 502 scopes may be thought of as a form of scope alias, in which the 503 addresses to which the domain name or URI resolve represent the 504 full scope of the mitigation. 506 If there is additional information available narrowing the scope 507 of any requested attack response, such as targeted port range, 508 protocol, or service, DOTS clients SHOULD include that information 509 in client mitigation requests. DOTS clients MAY also include 510 additional attack details. DOTS servers MAY ignore such 511 supplemental information when enabling countermeasures on the 512 mitigator. 514 As an active attack evolves, DOTS clients MUST be able to adjust 515 as necessary the scope of requested mitigation by refining the 516 scope of resources requiring mitigation. 518 A DOTS client may obtain the mitigation scope through direct 519 provisioning or through implementation-specific methods of 520 discovery. DOTS clients MUST support at least one mechanism to 521 obtain mitigation scope. 523 SIG-009 Mitigation Efficacy: When a mitigation request is active, 524 DOTS clients SHOULD transmit a metric of perceived mitigation 525 efficacy to the DOTS server. DOTS servers MAY use the efficacy 526 metric to adjust countermeasures activated on a mitigator on 527 behalf of a DOTS client. 529 SIG-010 Conflict Detection and Notification: Multiple DOTS clients 530 controlled by a single administrative entity may send conflicting 531 mitigation requests as a result of misconfiguration, operator 532 error, or compromised DOTS clients. DOTS servers in the same 533 administrative domain attempting to honor conflicting requests may 534 flap network route or DNS information, degrading the networks 535 attempting to participate in attack response with the DOTS 536 clients. DOTS servers in a single administrative domain SHALL 537 detect such conflicting requests, and SHALL notify the DOTS 538 clients in conflict. The notification SHOULD indicate the nature 539 and scope of the conflict, for example, the overlapping prefix 540 range in a conflicting mitigation request. 542 SIG-011 Network Address Translator Traversal: DOTS clients may be 543 deployed behind a Network Address Translator (NAT), and need to 544 communicate with DOTS servers through the NAT. DOTS protocols 545 MUST therefore be capable of traversing NATs. 547 If UDP is used as the transport for the DOTS signal channel, all 548 considerations in "Middlebox Traversal Guidelines" in [RFC8085] 549 apply to DOTS. Regardless of transport, DOTS protocols MUST 550 follow established best common practices established in BCP 127 551 for NAT traversal [RFC4787][RFC6888][RFC7857]. 553 2.3. Data Channel Requirements 555 The data channel is intended to be used for bulk data exchanges 556 between DOTS agents. Unlike the signal channel, the data channel is 557 not expected to be constructed to deal with attack conditions. As 558 the primary function of the data channel is data exchange, a reliable 559 transport is required in order for DOTS agents to detect data 560 delivery success or failure. 562 The data channel provides a protocol for DOTS configuration, 563 management. For example, a DOTS client may submit to a DOTS server a 564 collection of prefixes it wants to refer to by alias when requesting 565 mitigation, to which the server would respond with a success status 566 and the new prefix group alias, or an error status and message in the 567 event the DOTS client's data channel request failed. 569 DATA-001 Reliable transport: Messages sent over the data channel 570 MUST be delivered reliably, in order sent. 572 DATA-002 Data privacy and integrity: Transmissions over the data 573 channel are likely to contain operationally or privacy-sensitive 574 information or instructions from the remote DOTS agent. Theft or 575 modification of data channel transmissions could lead to 576 information leaks or malicious transactions on behalf of the 577 sending agent (see Section 4 below). Consequently data sent over 578 the data channel MUST be encrypted and authenticated using current 579 IETF best practices. DOTS servers MUST enable means to prevent 580 leaking operationally or privacy-sensitive data. Although 581 administrative entities participating in DOTS may detail what data 582 may be revealed to third-party DOTS agents, such considerations 583 are not in scope for this document. 585 DATA-003 Resource Configuration: To help meet the general and signal 586 channel requirements in Section 2.1 and Section 2.2, DOTS server 587 implementations MUST provide an interface to configure resource 588 identifiers, as described in SIG-007. DOTS server implementations 589 MAY expose additional configurability. Additional configurability 590 is implementation-specific. 592 DATA-004 Black- and whitelist management: DOTS servers MUST provide 593 methods for DOTS clients to manage black- and white-lists of 594 traffic destined for resources belonging to a client. 596 For example, a DOTS client should be able to create a black- or 597 whitelist entry, retrieve a list of current entries from either 598 list, update the content of either list, and delete entries as 599 necessary. 601 How a DOTS server authorizes DOTS client management of black- and 602 white-list entries is implementation-specific. 604 2.4. Security Requirements 606 DOTS must operate within a particularly strict security context, as 607 an insufficiently protected signal or data channel may be subject to 608 abuse, enabling or supplementing the very attacks DOTS purports to 609 mitigate. 611 SEC-001 Peer Mutual Authentication: DOTS agents MUST authenticate 612 each other before a DOTS signal or data channel is considered 613 valid. The method of authentication is not specified, but should 614 follow current industry best practices with respect to any 615 cryptographic mechanisms to authenticate the remote peer. 617 SEC-002 Message Confidentiality, Integrity and Authenticity: DOTS 618 protocols MUST take steps to protect the confidentiality, 619 integrity and authenticity of messages sent between client and 620 server. While specific transport- and message-level security 621 options are not specified, the protocols MUST follow current 622 industry best practices for encryption and message authentication. 624 In order for DOTS protocols to remain secure despite advancements 625 in cryptanalysis and traffic analysis, DOTS agents MUST be able to 626 negotiate the terms and mechanisms of protocol security, subject 627 to the interoperability and signal message size requirements in 628 Section 2.2. 630 While the interfaces between downstream DOTS server and upstream 631 DOTS client within a DOTS gateway are implementation-specific, 632 those interfaces nevertheless MUST provide security equivalent to 633 that of the signal channels bridged by gateways in the signaling 634 path. For example, when a DOTS gateway consisting of a DOTS 635 server and DOTS client is running on the same logical device, the 636 two DOTS agents could be implemented within the same process 637 security boundary. 639 SEC-003 Message Replay Protection: To prevent a passive attacker 640 from capturing and replaying old messages, and thereby potentially 641 disrupting or influencing the network policy of the receiving DOTS 642 agent's domain, DOTS protocols MUST provide a method for replay 643 detection and prevention. 645 Within the signal channel, messages MUST be uniquely identified 646 such that replayed or duplicated messages can be detected and 647 discarded. Unique mitigation requests MUST be processed at most 648 once. 650 SEC-004 Authorization: DOTS servers MUST authorize all messages from 651 DOTS clients which pertain to mitigation, configuration, 652 filtering, or status. 654 DOTS servers MUST reject mitigation requests with scopes which the 655 DOTS client is not authorized to manage. 657 Likewise, DOTS servers MUST refuse to allow creation, modification 658 or deletion of scope aliases and black-/white-lists when the DOTS 659 client is unauthorized. 661 The modes of authorization are implementation-specific. 663 2.5. Data Model Requirements 665 A well-structured DOTS data model is critical to the development of 666 successful DOTS protocols. 668 DM-001 Structure: The data model structure for the DOTS protocol MAY 669 be described by a single module, or be divided into related 670 collections of hierarchical modules and sub-modules. If the data 671 model structure is split across modules, those distinct modules 672 MUST allow references to describe the overall data model's 673 structural dependencies. 675 DM-002 Versioning: To ensure interoperability between DOTS protocol 676 implementations, data models MUST be versioned. How the protocols 677 represent data model versions is not defined in this document. 679 DM-003 Mitigation Status Representation: The data model MUST provide 680 the ability to represent a request for mitigation and the 681 withdrawal of such a request. The data model MUST also support a 682 representation of currently requested mitigation status, including 683 failures and their causes. 685 DM-004 Mitigation Scope Representation: The data model MUST support 686 representation of a requested mitigation's scope. As mitigation 687 scope may be represented in several different ways, per SIG-007 688 above, the data model MUST be capable of flexible representation 689 of mitigation scope. 691 DM-005 Mitigation Lifetime Representation: The data model MUST 692 support representation of a mitigation request's lifetime, 693 including mitigations with no specified end time. 695 DM-006 Mitigation Efficacy Representation: The data model MUST 696 support representation of a DOTS client's understanding of the 697 efficacy of a mitigation enabled through a mitigation request. 699 DM-007 Acceptable Signal Loss Representation: The data model MUST be 700 able to represent the DOTS agent's preference for acceptable 701 signal loss when establishing a signal channel, as described in 702 GEN-002. 704 DM-008 Heartbeat Interval Representation: The data model MUST be 705 able to represent the DOTS agent's preferred heartbeat interval, 706 which the client may include when establishing the signal channel, 707 as described in SIG-003. 709 DM-009 Relationship to Transport: The DOTS data model MUST NOT 710 depend on the specifics of any transport to represent fields in 711 the model. 713 3. Congestion Control Considerations 715 3.1. Signal Channel 717 As part of a protocol expected to operate over links affected by DDoS 718 attack traffic, the DOTS signal channel MUST NOT contribute 719 significantly to link congestion. To meet the signal channel 720 requirements above, DOTS signal channel implementations SHOULD 721 support connectionless transports. However, some connectionless 722 transports when deployed naively can be a source of network 723 congestion, as discussed in [RFC8085]. Signal channel 724 implementations using such connectionless transports, such as UDP, 725 therefore MUST include a congestion control mechanism. 727 Signal channel implementations using TCP may rely on built-in TCP 728 congestion control support. 730 3.2. Data Channel 732 As specified in DATA-001, the data channel requires reliable, in- 733 order message delivery. Data channel implementations using TCP may 734 rely on the TCP implementation's built-in congestion control 735 mechanisms. 737 4. Security Considerations 739 This document informs future protocols under development, and so does 740 not have security considerations of its own. However, operators 741 should be aware of potential risks involved in deploying DOTS. DOTS 742 agent impersonation and signal blocking are discussed here. 743 Additional DOTS security considerations may be found in 744 [I-D.ietf-dots-architecture] and DOTS protocol documents. 746 Impersonation of either DOTS server or DOTS client could have 747 catastrophic impact on operations in either domain. If an attacker 748 has the ability to impersonate a DOTS client, that attacker can 749 affect policy on the network path to the DOTS client's domain, up to 750 and including instantiation of blacklists blocking all inbound 751 traffic to networks for which the DOTS client is authorized to 752 request mitigation. 754 Similarly, an impersonated DOTS server may be able to act as a sort 755 of malicious DOTS gateway, intercepting requests from the downstream 756 DOTS client, and modifying them before transmission to the DOTS 757 server to inflict the desired impact on traffic to or from the DOTS 758 client's domain. Among other things, this malicious DOTS gateway 759 might receive and discard mitigation requests from the DOTS client, 760 ensuring no requested mitigation is ever applied. 762 As detailed in Section 2.4, DOTS implementations require mutual 763 authentication of DOTS agents in order to make agent impersonation 764 more difficult. However, impersonation may still be possible as a 765 result of credential theft, implementation flaws, or compromise of 766 DOTS agents. To detect misuse, DOTS operators should carefully 767 monitor and audit DOTS agents, while employing current secure network 768 communications best practices to reduce attack surface. 770 Blocking communication between DOTS agents has the potential to 771 disrupt the core function of DOTS, which is to request mitigation of 772 active or expected DDoS attacks. The DOTS signal channel is expected 773 to operate over congested inbound links, and, as described in 774 Section 2.2, the signal channel protocol must be designed for minimal 775 data transfer to reduce the incidence of signal blocking. 777 5. IANA Considerations 779 This document does not require any IANA action. 781 6. Contributors 783 Mohamed Boucadair 784 Orange 786 mohamed.boucadair@orange.com 788 Flemming Andreasen 789 Cisco Systems, Inc. 791 fandreas@cisco.com 793 Dave Dolson 794 Sandvine 796 ddolson@sandvine.com 798 7. Acknowledgments 800 Thanks to Roman Danyliw and Matt Richardson for careful reading and 801 feedback. 803 8. References 805 8.1. Normative References 807 [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, 808 DOI 10.17487/RFC0768, August 1980, 809 . 811 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 812 DOI 10.17487/RFC0791, September 1981, 813 . 815 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 816 RFC 793, DOI 10.17487/RFC0793, September 1981, 817 . 819 [RFC1035] Mockapetris, P., "Domain names - implementation and 820 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 821 November 1987, . 823 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 824 Communication Layers", STD 3, RFC 1122, 825 DOI 10.17487/RFC1122, October 1989, 826 . 828 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 829 DOI 10.17487/RFC1191, November 1990, 830 . 832 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 833 Requirement Levels", BCP 14, RFC 2119, 834 DOI 10.17487/RFC2119, March 1997, 835 . 837 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 838 Resource Identifier (URI): Generic Syntax", STD 66, 839 RFC 3986, DOI 10.17487/RFC3986, January 2005, 840 . 842 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 843 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 844 2006, . 846 [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing 847 (CIDR): The Internet Address Assignment and Aggregation 848 Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August 849 2006, . 851 [RFC4787] Audet, F., Ed. and C. Jennings, "Network Address 852 Translation (NAT) Behavioral Requirements for Unicast 853 UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January 854 2007, . 856 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 857 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 858 . 860 [RFC6888] Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa, 861 A., and H. Ashida, "Common Requirements for Carrier-Grade 862 NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888, 863 April 2013, . 865 [RFC7857] Penno, R., Perreault, S., Boucadair, M., Ed., Sivakumar, 866 S., and K. Naito, "Updates to Network Address Translation 867 (NAT) Behavioral Requirements", BCP 127, RFC 7857, 868 DOI 10.17487/RFC7857, April 2016, 869 . 871 [RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage 872 Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, 873 March 2017, . 875 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 876 Address Text Representation", RFC 5952, 877 DOI 10.17487/RFC5952, August 2010, 878 . 880 8.2. Informative References 882 [I-D.ietf-dots-architecture] 883 Mortensen, A., Andreasen, F., Reddy, T., 884 christopher_gray3@cable.comcast.com, c., Compton, R., and 885 N. Teague, "Distributed-Denial-of-Service Open Threat 886 Signaling (DOTS) Architecture", draft-ietf-dots- 887 architecture-05 (work in progress), October 2017. 889 [I-D.ietf-dots-use-cases] 890 Dobbins, R., Migault, D., Fouant, S., Moskowitz, R., 891 Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS 892 Open Threat Signaling", draft-ietf-dots-use-cases-09 (work 893 in progress), November 2017. 895 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 896 A., Peterson, J., Sparks, R., Handley, M., and E. 897 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 898 DOI 10.17487/RFC3261, June 2002, 899 . 901 [RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session 902 Initiation Protocol (SIP) Back-to-Back User Agents", 903 RFC 7092, DOI 10.17487/RFC7092, December 2013, 904 . 906 [RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet 907 Denial-of-Service Considerations", RFC 4732, 908 DOI 10.17487/RFC4732, December 2006, 909 . 911 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", 912 FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, 913 . 915 Authors' Addresses 917 Andrew Mortensen 918 Arbor Networks 919 2727 S. State St 920 Ann Arbor, MI 48104 921 United States 923 Email: amortensen@arbor.net 925 Robert Moskowitz 926 Huawei 927 Oak Park, MI 42837 928 United States 930 Email: rgm@htt-consult.com 932 Tirumaleswar Reddy 933 McAfee 934 Embassy Golf Link Business Park 935 Bangalore, Karnataka 560071 936 India 938 Email: TirumaleswarReddy_Konda@McAfee.com