DOTS A. Mortensen Internet-Draft Arbor Networks Intended status: Informational R. Moskowitz Expires: August 11, 2018 Huawei T. Reddy McAfee February 07, 2018 Distributed Denial of Service (DDoS) Open Threat Signaling Requirements draft-ietf-dots-requirements-13 Abstract This document defines the requirements for the Distributed Denial of Service (DDoS) Open Threat Signaling (DOTS) protocols enabling coordinated response to DDoS attacks. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on August 11, 2018. Copyright Notice Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of Mortensen, et al. Expires August 11, 2018 [Page 1] Internet-Draft DOTS Requirements February 2018 the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Context and Motivation . . . . . . . . . . . . . . . . . 2 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5 2.1. General Requirements . . . . . . . . . . . . . . . . . . 6 2.2. Signal Channel Requirements . . . . . . . . . . . . . . . 7 2.3. Data Channel Requirements . . . . . . . . . . . . . . . . 12 2.4. Security Requirements . . . . . . . . . . . . . . . . . . 13 2.5. Data Model Requirements . . . . . . . . . . . . . . . . . 14 3. Congestion Control Considerations . . . . . . . . . . . . . . 16 3.1. Signal Channel . . . . . . . . . . . . . . . . . . . . . 16 3.2. Data Channel . . . . . . . . . . . . . . . . . . . . . . 16 4. Security Considerations . . . . . . . . . . . . . . . . . . . 16 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 17 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 8.1. Normative References . . . . . . . . . . . . . . . . . . 17 8.2. Informative References . . . . . . . . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 1. Introduction 1.1. Context and Motivation Distributed Denial of Service (DDoS) attacks afflict networks of all kinds, plaguing network operators at service providers and enterprises around the world. High-volume attacks saturating inbound links are now common, as attack scale and frequency continue to increase. The prevalence and impact of these DDoS attacks has led to an increased focus on coordinated attack response. However, many enterprises lack the resources or expertise to operate on-premises attack mitigation solutions themselves, or are constrained by local bandwidth limitations. To address such gaps, service providers have begun to offer on-demand traffic scrubbing services, which are designed to separate the DDoS attack traffic from legitimate traffic and forward only the latter. Today, these services offer proprietary interfaces for subscribers to request attack mitigation. Such proprietary interfaces tie a subscriber to a service while also limiting the network elements Mortensen, et al. Expires August 11, 2018 [Page 2] Internet-Draft DOTS Requirements February 2018 capable of participating in the attack mitigation. As a result of signaling interface incompatibility, attack responses may be fragmented or otherwise incomplete, leaving operators in the attack path unable to assist in the defense. A standardized method to coordinate a real-time response among involved operators will increase the speed and effectiveness of DDoS attack mitigation, and reduce the impact of these attacks. This document describes the required characteristics of protocols that enable attack coordination and mitigation of DDoS attacks. DDoS Open Threat Signaling (DOTS) communicates the need for defensive action in anticipation of or in response to an attack, but does not dictate the implementation of these actions. The requirements in this document are derived from [I-D.ietf-dots-use-cases] and [I-D.ietf-dots-architecture]. 1.2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. This document adopts the following terms: DDoS: A distributed denial-of-service attack, in which traffic originating from multiple sources is directed at a target on a network. DDoS attacks are intended to cause a negative impact on the availability and/or other functionality of an attack target. Denial-of-service considerations are discussed in detail in [RFC4732]. DDoS attack target: A network connected entity with a finite set of resources, such as network bandwidth, memory or CPU, that is the target of a DDoS attack. Potential targets include (but are not limited to) network elements, network links, servers, and services. DDoS attack telemetry: Collected measurements and behavioral characteristics defining the nature of a DDoS attack. Countermeasure: An action or set of actions focused on recognizing and filtering out specific types of DDoS attack traffic while passing legitimate traffic to the attack target. Distinct countermeasures can be layered to defend against attacks combining multiple DDoS attack types. Mortensen, et al. Expires August 11, 2018 [Page 3] Internet-Draft DOTS Requirements February 2018 Mitigation: A set of countermeasures enforced against traffic destined for the target or targets of a detected or reported DDoS attack, where countermeasure enforcement is managed by an entity in the network path between attack sources and the attack target. Mitigation methodology is out of scope for this document. Mitigator: An entity, typically a network element, capable of performing mitigation of a detected or reported DDoS attack. The means by which this entity performs these mitigations and how they are requested of it are out of scope. The mitigator and DOTS server receiving a mitigation request are assumed to belong to the same administrative entity. DOTS client: A DOTS-aware software module responsible for requesting attack response coordination with other DOTS-aware elements. DOTS server: A DOTS-aware software module handling and responding to messages from DOTS clients. The DOTS server enables mitigation on behalf of the DOTS client, if requested, by communicating the DOTS client's request to the mitigator and returning selected mitigator feedback to the requesting DOTS client. DOTS agent: Any DOTS-aware software module capable of participating in a DOTS signal or data channel. It can be a DOTS client, DOTS server, or, as a logical agent, a DOTS gateway. DOTS gateway: A DOTS-aware software module resulting from the logical concatenation of the functionality of a DOTS server and a DOTS client into a single DOTS agent. This functionality is analogous to a Session Initiation Protocol (SIP) [RFC3261] Back- to-Back User Agent (B2BUA) [RFC7092]. A DOTS gateway has a client-facing side, which behaves as a DOTS server for downstream clients, and a server-facing side, which performs the role of DOTS client for upstream DOTS servers. Client-domain DOTS gateways are DOTS gateways that are in the DOTS client's domain, while server- domain DOTS gateways denote DOTS gateways that are in the DOTS server's domain. DOTS gateways are described further in [I-D.ietf-dots-architecture]. Signal channel: A bidirectional, mutually authenticated communication channel between DOTS agents that is resilient even in conditions leading to severe packet loss, such as a volumetric DDoS attack causing network congestion. DOTS signal: A concise authenticated status/control message transmitted over the signal channel between DOTS agents, used to indicate the client's need for mitigation, as well as to convey the status of any requested mitigation. Mortensen, et al. Expires August 11, 2018 [Page 4] Internet-Draft DOTS Requirements February 2018 Heartbeat: A message transmitted between DOTS agents over the signal channel, used as a keep-alive and to measure peer health. Data channel: A bidirectional, mutually authentication communincation channel between two DOTS agents used for infrequent but reliable bulk exchange of data not easily or appropriately communicated through the signal channel under attack conditions. Filter: A specification of a matching network traffic flow or set of flows. The filter will typically have a policy associated with it, e.g., rate-limiting or discarding matching traffic [RFC4949]. Blacklist: A list of filters indicating sources from which traffic should be blocked, regardless of traffic content. Whitelist: A list of filters indicating sources from which traffic should always be allowed, regardless of contradictory data gleaned in a detected attack. Multi-homed DOTS client: A DOTS client exchanging messages with multiple DOTS servers, each in a separate administrative domain. 2. Requirements This section describes the required features and characteristics of the DOTS protocols. The DOTS protocols enable and manage mitigation on behalf of a network domain or resource which is or may become the focus of a DDoS attack. An active DDoS attack against the entity controlling the DOTS client need not be present before establishing a communication channel between DOTS agents. Indeed, establishing a relationship with peer DOTS agents during normal network conditions provides the foundation for more rapid attack response against future attacks, as all interactions setting up DOTS, including any business or service level agreements, are already complete. Reachability information of peer DOTS agents is provisioned to a DOTS client using a variety of manual or dynamic methods. Once a relationship between DOTS agents is established, regular communication between DOTS clients and servers enables a common understanding of the DOTS agents' health and activity. The DOTS protocol must at a minimum make it possible for a DOTS client to request aid mounting a defense, coordinated by a DOTS server, against a suspected attack, signaling within or between domains as requested by local operators. DOTS clients should similarly be able to withdraw aid requests. DOTS requires no justification from DOTS clients for requests for help, nor do DOTS Mortensen, et al. Expires August 11, 2018 [Page 5] Internet-Draft DOTS Requirements February 2018 clients need to justify withdrawing help requests: the decision is local to the DOTS clients' domain. Multi-homed DOTS clients must be able to select the appropriate DOTS server(s) to which a mitigation request is to be sent. The method for selecting the appropriate DOTS server in a multi-homed environment is out of scope. DOTS protocol implementations face competing operational goals when maintaining this bidirectional communication stream. On the one hand, DOTS must include protections ensuring message confidentiality, integrity and authenticity to keep the protocols from becoming additional vectors for the very attacks it is meant to help fight off. On the other hand, the protocol must be resilient under extremely hostile network conditions, providing continued contact between DOTS agents even as attack traffic saturates the link. Such resiliency may be developed several ways, but characteristics such as small message size, asynchronous, redundant message delivery and minimal connection overhead (when possible given local network policy) will tend to contribute to the robustness demanded by a viable DOTS protocol. Operators of peer DOTS-enabled domains may enable quality- or class-of-service traffic tagging to increase the probability of successful DOTS signal delivery, but DOTS does not require such policies be in place, and should be viable in their absence. The DOTS server and client must also have some standardized method of defining the scope of any mitigation, as well as managing other mitigation-related configuration. Finally, DOTS should be sufficiently extensible to meet future needs in coordinated attack defense, although this consideration is necessarily superseded by the other operational requirements. 2.1. General Requirements GEN-001 Extensibility: Protocols and data models developed as part of DOTS MUST be extensible in order to keep DOTS adaptable to operational and proprietary DDoS defenses. Future extensions MUST be backward compatible. DOTS protocols MUST use a version number system to distinguish protocol revisions. Implementations of older protocol versions SHOULD ignore information added to DOTS messages as part of newer protocol versions. GEN-002 Resilience and Robustness: The signaling protocol MUST be designed to maximize the probability of signal delivery even under the severely constrained network conditions caused by particular attack traffic. The protocol MUST be resilient, that is, continue operating despite message loss and out-of-order or redundant message delivery. In support of signaling protocol robustness, Mortensen, et al. Expires August 11, 2018 [Page 6] Internet-Draft DOTS Requirements February 2018 DOTS signals SHOULD be conveyed over a transport not susceptible to Head of Line Blocking. GEN-003 Bulk Data Exchange: Infrequent bulk data exchange between DOTS agents can also significantly augment attack response coordination, permitting such tasks as population of black- or white-listed source addresses; address or prefix group aliasing; exchange of incident reports; and other hinting or configuration supplementing attack response. As the resilience requirements for the DOTS signal channel mandate small signal message size, a separate, secure data channel utilizing a reliable transport protocol MUST be used for bulk data exchange. GEN-004 Mitigation Hinting: DOTS clients may have access to attack details which can be used to inform mitigation techniques. Example attack details might include locally collected fingerprints for an on-going attack, or anticipated or active attack focal points based on other threat intelligence. DOTS clients MAY send mitigation hints derived from attack details to DOTS servers, in the full understanding that the DOTS server MAY ignore mitigation hints. Mitigation hints MAY be transmitted across either signal or data channel. DOTS server treatment of mitigation hints, and how such hints shape mitigation, are implementation-specific. GEN-005 Loop Handling: In specific scenarios, it may be possible for communication between DOTS agents to loop, for example as a result of misconfiguration or aggressive caching. Signal and data channel implementations should be prepared to detect and terminate such loops to prevent service disruption. 2.2. Signal Channel Requirements SIG-001 Use of Common Transport Protocols: DOTS MUST operate over common widely deployed and standardized transport protocols. While connectionless transport such as the User Datagram Protocol (UDP) [RFC0768] SHOULD be used for the signal channel, the Transmission Control Protocol (TCP) [RFC0793] MAY be used if necessary due to network policy or middlebox capabilities or configurations. SIG-002 Sub-MTU Message Size: To avoid message fragmentation and the consequently decreased probability of message delivery over a congested link, signaling protocol message size MUST be kept under signaling Path Maximum Transmission Unit (PMTU), including the Mortensen, et al. Expires August 11, 2018 [Page 7] Internet-Draft DOTS Requirements February 2018 byte overhead of any encapsulation, transport headers, and transport- or message-level security. DOTS agents SHOULD attempt to learn the PMTU through mechanisms such as Path MTU Discovery [RFC1191] or Packetization Layer Path MTU Discovery [RFC4821]. If the PMTU cannot be discovered, DOTS agents SHOULD assume a PMTU of 1280 bytes. If IPv4 support on legacy or otherwise unusual networks is a consideration and PMTU is unknown, DOTS implementations MAY rely on a PMTU of 576 bytes, as discussed in [RFC0791] and [RFC1122]. SIG-003 Bidirectionality: To support peer health detection, to maintain an active signal channel, and increase the probability of signal delivery during an attack, the signal channel MUST be bidirectional, with client and server transmitting signals to each other at regular intervals, regardless of any client request for mitigation. Unidirectional messages MUST be supported within the bidirectional signal channel to allow for unsolicited message delivery, enabling asynchronous notifications between DOTS agents. SIG-004 Channel Health Monitoring: DOTS agents MUST support exchange of heartbeat messages over the signal channel to monitor channel health. Peer DOTS agents SHOULD regularly send heartbeats to each other while a mitigation request is active. The heartbeat interval during active mitigation could be negotiable, but SHOULD be frequent enough to maintain any on-path NAT or Firewall bindings during mitigation. To support scenarios in which loss of heartbeat is used to trigger mitigation, and to keep the channel active, DOTS clients MAY solicit heartbeat exchanges after successful mutual authentication. When DOTS agents are exchanging heartbeats and no mitigation request is active, either agent MAY request changes to the heartbeat rate. For example, a DOTS server might want to reduce heartbeat frequency or cease heartbeat exchanges when an active DOTS client has not requested mitigation, in order to control load. Following mutual authentication, a signal channel MUST be considered active until a DOTS agent explicitly ends the session, or either DOTS agent fails to receive heartbeats from the other after a mutually agreed upon retransmission procedure has been exhausted. Because heartbeat loss is much more likely during volumetric attack, DOTS agents SHOULD avoid signal channel termination when mitigation is active and heartbeats are not received by either DOTS agent for an extended period. In such circumstances, DOTS clients MAY attempt to reestablish the signal channel, but SHOULD continue to send heartbeats so that the DOTS Mortensen, et al. Expires August 11, 2018 [Page 8] Internet-Draft DOTS Requirements February 2018 server knows the session is still alive. DOTS servers are assumed to have the ability to monitor the attack, using feedback from the mitigator and other available sources, and MAY use the absence of attack traffic and lack of client heartbeats as an indication the signal channel is defunct. SIG-005 Channel Redirection: In order to increase DOTS operational flexibility and scalability, DOTS servers SHOULD be able to redirect DOTS clients to another DOTS server at any time. DOTS clients MUST NOT assume the redirection target DOTS server shares security state with the redirecting DOTS server. DOTS clients are free to attempt abbreviated security negotiation methods supported by the protocol, such as DTLS session resumption, but MUST be prepared to negotiate new security state with the redirection target DOTS server. Due to the increased likelihood of packet loss caused by link congestion during an attack, DOTS servers SHOULD NOT redirect while mitigation is enabled during an active attack against a target in the DOTS client's domain. SIG-006 Mitigation Requests and Status: Authorized DOTS clients MUST be able to request scoped mitigation from DOTS servers. DOTS servers MUST send status to the DOTS clients about mitigation requests. If a DOTS server rejects an authorized request for mitigation, the DOTS server MUST include a reason for the rejection in the status message sent to the client. Due to the higher likelihood of packet loss during a DDoS attack, DOTS servers SHOULD regularly send mitigation status to authorized DOTS clients which have requested and been granted mitigation, regardless of client requests for mitigation status. When DOTS client-requested mitigation is active, DOTS server status messages SHOULD include the following mitigation metrics: * Total number of packets blocked by the mitigation * Current number of packets per second blocked * Total number of bytes blocked * Current number of bytes per second blocked DOTS clients MAY take these metrics into account when determining whether to ask the DOTS server to cease mitigation. Mortensen, et al. Expires August 11, 2018 [Page 9] Internet-Draft DOTS Requirements February 2018 A DOTS client MAY withdraw a mitigation request at any time, regardless of whether mitigation is currently active. The DOTS server MUST immediately acknowledge a DOTS client's request to stop mitigation. To protect against route or DNS flapping caused by a client rapidly toggling mitigation, and to dampen the effect of oscillating attacks, DOTS servers MAY allow mitigation to continue for a limited period after acknowledging a DOTS client's withdrawal of a mitigation request. During this period, DOTS server status messages SHOULD indicate that mitigation is active but terminating. The initial active-but-terminating period is implementation- and deployment- specific, but SHOULD be sufficiently long to absorb latency incurred by route propagation. If the client requests mitigation again before the initial active-but-terminating period elapses, the DOTS server MAY exponentially increase the active- but-terminating period up to a maximum of 300 seconds (5 minutes). After the active-but-terminating period elapses, the DOTS server MUST treat the mitigation as terminated, as the DOTS client is no longer responsible for the mitigation. SIG-007 Mitigation Lifetime: DOTS servers MUST support mitigations for a negotiated time interval, and MUST terminate a mitigation when the lifetime elapses. DOTS servers also MUST support renewal of mitigation lifetimes in mitigation requests from DOTS clients, allowing clients to extend mitigation as necessary for the duration of an attack. DOTS servers MUST treat a mitigation terminated due to lifetime expiration exactly as if the DOTS client originating the mitigation had asked to end the mitigation, including the active- but-terminating period, as described above in SIG-005. DOTS clients MUST include a mitigation lifetime in all mitigation requests. DOTS servers SHOULD support indefinite mitigation lifetimes, enabling architectures in which the mitigator is always in the traffic path to the resources for which the DOTS client is requesting protection. DOTS clients MUST be prepared to not be granted mitigations with indefinite lifetimes. DOTS servers MAY refuse mitigations with indefinite lifetimes, for policy reasons. The reasons themselves are out of scope. If the DOTS server does not grant a mitigation request with an indefinite mitigation lifetime, it MUST set the lifetime to a value that is configured Mortensen, et al. Expires August 11, 2018 [Page 10] Internet-Draft DOTS Requirements February 2018 locally. That value MUST be returned in a reply to the requesting DOTS client. SIG-008 Mitigation Scope: DOTS clients MUST indicate desired mitigation scope. The scope type will vary depending on the resources requiring mitigation. All DOTS agent implementations MUST support the following required scope types: * IPv4 prefixes in CIDR notation [RFC4632] * IPv6 prefixes [RFC4291][RFC5952] * Domain names [RFC1035] The following mitigation scope types are OPTIONAL: * Uniform Resource Identifiers [RFC3986] DOTS servers MUST be able to resolve domain names and (when supported) URIs. How name resolution is managed on the DOTS server is implementation-specific. DOTS agents MUST support mitigation scope aliases, allowing DOTS clients and servers to refer to collections of protected resources by an opaque identifier created through the data channel, direct configuration, or other means. Domain name and URI mitigation scopes may be thought of as a form of scope alias, in which the addresses to which the domain name or URI resolve represent the full scope of the mitigation. If there is additional information available narrowing the scope of any requested attack response, such as targeted port range, protocol, or service, DOTS clients SHOULD include that information in client mitigation requests. DOTS clients MAY also include additional attack details. DOTS servers MAY ignore such supplemental information when enabling countermeasures on the mitigator. As an active attack evolves, DOTS clients MUST be able to adjust as necessary the scope of requested mitigation by refining the scope of resources requiring mitigation. A DOTS client may obtain the mitigation scope through direct provisioning or through implementation-specific methods of discovery. DOTS clients MUST support at least one mechanism to obtain mitigation scope. Mortensen, et al. Expires August 11, 2018 [Page 11] Internet-Draft DOTS Requirements February 2018 SIG-009 Mitigation Efficacy: When a mitigation request is active, DOTS clients SHOULD transmit a metric of perceived mitigation efficacy to the DOTS server. DOTS servers MAY use the efficacy metric to adjust countermeasures activated on a mitigator on behalf of a DOTS client. SIG-010 Conflict Detection and Notification: Multiple DOTS clients controlled by a single administrative entity may send conflicting mitigation requests as a result of misconfiguration, operator error, or compromised DOTS clients. DOTS servers in the same administrative domain attempting to honor conflicting requests may flap network route or DNS information, degrading the networks attempting to participate in attack response with the DOTS clients. DOTS servers in a single administrative domain SHALL detect such conflicting requests, and SHALL notify the DOTS clients in conflict. The notification SHOULD indicate the nature and scope of the conflict, for example, the overlapping prefix range in a conflicting mitigation request. SIG-011 Network Address Translator Traversal: DOTS clients may be deployed behind a Network Address Translator (NAT), and need to communicate with DOTS servers through the NAT. DOTS protocols MUST therefore be capable of traversing NATs. If UDP is used as the transport for the DOTS signal channel, all considerations in "Middlebox Traversal Guidelines" in [RFC8085] apply to DOTS. Regardless of transport, DOTS protocols MUST follow established best common practices established in BCP 127 for NAT traversal [RFC4787][RFC6888][RFC7857]. 2.3. Data Channel Requirements The data channel is intended to be used for bulk data exchanges between DOTS agents. Unlike the signal channel, the data channel is not expected to be constructed to deal with attack conditions. As the primary function of the data channel is data exchange, a reliable transport is required in order for DOTS agents to detect data delivery success or failure. The data channel provides a protocol for DOTS configuration, management. For example, a DOTS client may submit to a DOTS server a collection of prefixes it wants to refer to by alias when requesting mitigation, to which the server would respond with a success status and the new prefix group alias, or an error status and message in the event the DOTS client's data channel request failed. DATA-001 Reliable transport: Messages sent over the data channel MUST be delivered reliably, in order sent. Mortensen, et al. Expires August 11, 2018 [Page 12] Internet-Draft DOTS Requirements February 2018 DATA-002 Data privacy and integrity: Transmissions over the data channel are likely to contain operationally or privacy-sensitive information or instructions from the remote DOTS agent. Theft or modification of data channel transmissions could lead to information leaks or malicious transactions on behalf of the sending agent (see Section 4 below). Consequently data sent over the data channel MUST be encrypted and authenticated using current IETF best practices. DOTS servers MUST enable means to prevent leaking operationally or privacy-sensitive data. Although administrative entities participating in DOTS may detail what data may be revealed to third-party DOTS agents, such considerations are not in scope for this document. DATA-003 Resource Configuration: To help meet the general and signal channel requirements in Section 2.1 and Section 2.2, DOTS server implementations MUST provide an interface to configure resource identifiers, as described in SIG-007. DOTS server implementations MAY expose additional configurability. Additional configurability is implementation-specific. DATA-004 Black- and whitelist management: DOTS servers MUST provide methods for DOTS clients to manage black- and white-lists of traffic destined for resources belonging to a client. For example, a DOTS client should be able to create a black- or whitelist entry, retrieve a list of current entries from either list, update the content of either list, and delete entries as necessary. How a DOTS server authorizes DOTS client management of black- and white-list entries is implementation-specific. 2.4. Security Requirements DOTS must operate within a particularly strict security context, as an insufficiently protected signal or data channel may be subject to abuse, enabling or supplementing the very attacks DOTS purports to mitigate. SEC-001 Peer Mutual Authentication: DOTS agents MUST authenticate each other before a DOTS signal or data channel is considered valid. The method of authentication is not specified, but should follow current industry best practices with respect to any cryptographic mechanisms to authenticate the remote peer. SEC-002 Message Confidentiality, Integrity and Authenticity: DOTS protocols MUST take steps to protect the confidentiality, integrity and authenticity of messages sent between client and Mortensen, et al. Expires August 11, 2018 [Page 13] Internet-Draft DOTS Requirements February 2018 server. While specific transport- and message-level security options are not specified, the protocols MUST follow current industry best practices for encryption and message authentication. In order for DOTS protocols to remain secure despite advancements in cryptanalysis and traffic analysis, DOTS agents MUST be able to negotiate the terms and mechanisms of protocol security, subject to the interoperability and signal message size requirements in Section 2.2. While the interfaces between downstream DOTS server and upstream DOTS client within a DOTS gateway are implementation-specific, those interfaces nevertheless MUST provide security equivalent to that of the signal channels bridged by gateways in the signaling path. For example, when a DOTS gateway consisting of a DOTS server and DOTS client is running on the same logical device, the two DOTS agents could be implemented within the same process security boundary. SEC-003 Message Replay Protection: To prevent a passive attacker from capturing and replaying old messages, and thereby potentially disrupting or influencing the network policy of the receiving DOTS agent's domain, DOTS protocols MUST provide a method for replay detection and prevention. Within the signal channel, messages MUST be uniquely identified such that replayed or duplicated messages can be detected and discarded. Unique mitigation requests MUST be processed at most once. SEC-004 Authorization: DOTS servers MUST authorize all messages from DOTS clients which pertain to mitigation, configuration, filtering, or status. DOTS servers MUST reject mitigation requests with scopes which the DOTS client is not authorized to manage. Likewise, DOTS servers MUST refuse to allow creation, modification or deletion of scope aliases and black-/white-lists when the DOTS client is unauthorized. The modes of authorization are implementation-specific. 2.5. Data Model Requirements A well-structured DOTS data model is critical to the development of successful DOTS protocols. Mortensen, et al. Expires August 11, 2018 [Page 14] Internet-Draft DOTS Requirements February 2018 DM-001 Structure: The data model structure for the DOTS protocol MAY be described by a single module, or be divided into related collections of hierarchical modules and sub-modules. If the data model structure is split across modules, those distinct modules MUST allow references to describe the overall data model's structural dependencies. DM-002 Versioning: To ensure interoperability between DOTS protocol implementations, data models MUST be versioned. How the protocols represent data model versions is not defined in this document. DM-003 Mitigation Status Representation: The data model MUST provide the ability to represent a request for mitigation and the withdrawal of such a request. The data model MUST also support a representation of currently requested mitigation status, including failures and their causes. DM-004 Mitigation Scope Representation: The data model MUST support representation of a requested mitigation's scope. As mitigation scope may be represented in several different ways, per SIG-007 above, the data model MUST be capable of flexible representation of mitigation scope. DM-005 Mitigation Lifetime Representation: The data model MUST support representation of a mitigation request's lifetime, including mitigations with no specified end time. DM-006 Mitigation Efficacy Representation: The data model MUST support representation of a DOTS client's understanding of the efficacy of a mitigation enabled through a mitigation request. DM-007 Acceptable Signal Loss Representation: The data model MUST be able to represent the DOTS agent's preference for acceptable signal loss when establishing a signal channel, as described in GEN-002. DM-008 Heartbeat Interval Representation: The data model MUST be able to represent the DOTS agent's preferred heartbeat interval, which the client may include when establishing the signal channel, as described in SIG-003. DM-009 Relationship to Transport: The DOTS data model MUST NOT depend on the specifics of any transport to represent fields in the model. Mortensen, et al. Expires August 11, 2018 [Page 15] Internet-Draft DOTS Requirements February 2018 3. Congestion Control Considerations 3.1. Signal Channel As part of a protocol expected to operate over links affected by DDoS attack traffic, the DOTS signal channel MUST NOT contribute significantly to link congestion. To meet the signal channel requirements above, DOTS signal channel implementations SHOULD support connectionless transports. However, some connectionless transports when deployed naively can be a source of network congestion, as discussed in [RFC8085]. Signal channel implementations using such connectionless transports, such as UDP, therefore MUST include a congestion control mechanism. Signal channel implementations using TCP may rely on built-in TCP congestion control support. 3.2. Data Channel As specified in DATA-001, the data channel requires reliable, in- order message delivery. Data channel implementations using TCP may rely on the TCP implementation's built-in congestion control mechanisms. 4. Security Considerations This document informs future protocols under development, and so does not have security considerations of its own. However, operators should be aware of potential risks involved in deploying DOTS. DOTS agent impersonation and signal blocking are discussed here. Additional DOTS security considerations may be found in [I-D.ietf-dots-architecture] and DOTS protocol documents. Impersonation of either DOTS server or DOTS client could have catastrophic impact on operations in either domain. If an attacker has the ability to impersonate a DOTS client, that attacker can affect policy on the network path to the DOTS client's domain, up to and including instantiation of blacklists blocking all inbound traffic to networks for which the DOTS client is authorized to request mitigation. Similarly, an impersonated DOTS server may be able to act as a sort of malicious DOTS gateway, intercepting requests from the downstream DOTS client, and modifying them before transmission to the DOTS server to inflict the desired impact on traffic to or from the DOTS client's domain. Among other things, this malicious DOTS gateway might receive and discard mitigation requests from the DOTS client, ensuring no requested mitigation is ever applied. Mortensen, et al. Expires August 11, 2018 [Page 16] Internet-Draft DOTS Requirements February 2018 As detailed in Section 2.4, DOTS implementations require mutual authentication of DOTS agents in order to make agent impersonation more difficult. However, impersonation may still be possible as a result of credential theft, implementation flaws, or compromise of DOTS agents. To detect misuse, DOTS operators should carefully monitor and audit DOTS agents, while employing current secure network communications best practices to reduce attack surface. Blocking communication between DOTS agents has the potential to disrupt the core function of DOTS, which is to request mitigation of active or expected DDoS attacks. The DOTS signal channel is expected to operate over congested inbound links, and, as described in Section 2.2, the signal channel protocol must be designed for minimal data transfer to reduce the incidence of signal blocking. 5. IANA Considerations This document does not require any IANA action. 6. Contributors Mohamed Boucadair Orange mohamed.boucadair@orange.com Flemming Andreasen Cisco Systems, Inc. fandreas@cisco.com Dave Dolson Sandvine ddolson@sandvine.com 7. Acknowledgments Thanks to Roman Danyliw and Matt Richardson for careful reading and feedback. 8. References 8.1. Normative References [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI 10.17487/RFC0768, August 1980, . Mortensen, et al. Expires August 11, 2018 [Page 17] Internet-Draft DOTS Requirements February 2018 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI 10.17487/RFC0791, September 1981, . [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC 793, DOI 10.17487/RFC0793, September 1981, . [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, . [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, DOI 10.17487/RFC1122, October 1989, . [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, DOI 10.17487/RFC1191, November 1990, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, . [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2006, . [RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing (CIDR): The Internet Address Assignment and Aggregation Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August 2006, . [RFC4787] Audet, F., Ed. and C. Jennings, "Network Address Translation (NAT) Behavioral Requirements for Unicast UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January 2007, . [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, . Mortensen, et al. Expires August 11, 2018 [Page 18] Internet-Draft DOTS Requirements February 2018 [RFC6888] Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa, A., and H. Ashida, "Common Requirements for Carrier-Grade NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888, April 2013, . [RFC7857] Penno, R., Perreault, S., Boucadair, M., Ed., Sivakumar, S., and K. Naito, "Updates to Network Address Translation (NAT) Behavioral Requirements", BCP 127, RFC 7857, DOI 10.17487/RFC7857, April 2016, . [RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, March 2017, . [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 Address Text Representation", RFC 5952, DOI 10.17487/RFC5952, August 2010, . 8.2. Informative References [I-D.ietf-dots-architecture] Mortensen, A., Andreasen, F., Reddy, T., christopher_gray3@cable.comcast.com, c., Compton, R., and N. Teague, "Distributed-Denial-of-Service Open Threat Signaling (DOTS) Architecture", draft-ietf-dots- architecture-05 (work in progress), October 2017. [I-D.ietf-dots-use-cases] Dobbins, R., Migault, D., Fouant, S., Moskowitz, R., Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS Open Threat Signaling", draft-ietf-dots-use-cases-09 (work in progress), November 2017. [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, DOI 10.17487/RFC3261, June 2002, . [RFC7092] Kaplan, H. and V. Pascual, "A Taxonomy of Session Initiation Protocol (SIP) Back-to-Back User Agents", RFC 7092, DOI 10.17487/RFC7092, December 2013, . Mortensen, et al. Expires August 11, 2018 [Page 19] Internet-Draft DOTS Requirements February 2018 [RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet Denial-of-Service Considerations", RFC 4732, DOI 10.17487/RFC4732, December 2006, . [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, . Authors' Addresses Andrew Mortensen Arbor Networks 2727 S. State St Ann Arbor, MI 48104 United States Email: amortensen@arbor.net Robert Moskowitz Huawei Oak Park, MI 42837 United States Email: rgm@htt-consult.com Tirumaleswar Reddy McAfee Embassy Golf Link Business Park Bangalore, Karnataka 560071 India Email: TirumaleswarReddy_Konda@McAfee.com Mortensen, et al. Expires August 11, 2018 [Page 20]