DOTS A. Mortensen
Internet-Draft Arbor Networks
Intended status: Informational R. Moskowitz
Expires: July 6, 2018 Huawei
T. Reddy
McAfee, Inc.
January 02, 2018
Distributed Denial of Service (DDoS) Open Threat Signaling Requirements
draft-ietf-dots-requirements-10
Abstract
This document defines the requirements for the Distributed Denial of
Service (DDoS) Open Threat Signaling (DOTS) protocols coordinating
attack response against 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
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This Internet-Draft will expire on July 6, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Context and Motivation . . . . . . . . . . . . . . . . . 2
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. General Requirements . . . . . . . . . . . . . . . . . . 7
2.2. Signal Channel Requirements . . . . . . . . . . . . . . . 8
2.3. Data Channel Requirements . . . . . . . . . . . . . . . . 12
2.4. Security Requirements . . . . . . . . . . . . . . . . . . 13
2.5. Data Model Requirements . . . . . . . . . . . . . . . . . 15
3. Congestion Control Considerations . . . . . . . . . . . . . . 16
3.1. Signal Channel . . . . . . . . . . . . . . . . . . . . . 16
3.2. Data Channel . . . . . . . . . . . . . . . . . . . . . . 16
4. Security Considerations . . . . . . . . . . . . . . . . . . . 16
5. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 17
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.1. Normative References . . . . . . . . . . . . . . . . . . 17
7.2. Informative References . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
1.1. Context and Motivation
Distributed Denial of Service (DDoS) attacks continue to plague
network operators around the globe, from Tier-1 service providers on
down to enterprises and small businesses. Attack scale and frequency
similarly have continued to increase, in part as a result of software
vulnerabilities leading to reflection and amplification attacks.
High-volume attacks saturating inbound links are now common, and the
impact of larger-scale attacks attract the attention of international
press agencies.
The greater impact of contemporary DDoS attacks has led to increased
focus on coordinated attack response. Many institutions and
enterprises lack the resources or expertise to operate on-premises
attack mitigation solutions themselves, or simply find themselves
constrained by local bandwidth limitations. To address such gaps,
security service providers have begun to offer on-demand traffic
scrubbing services, which aim to separate the DDoS traffic from
legitimate traffic and forward only the latter. Today each such
service offers a proprietary invocation interface for subscribers to
request attack mitigation, tying subscribers to proprietary signaling
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implementations while also limiting the subset of network elements
capable of participating in the attack mitigation. As a result of
signaling interface incompatibility, attack responses may be
fragmentary or otherwise incomplete, leaving key players in the
attack path unable to assist in the defense.
The lack of a common method to coordinate a real-time response among
involved actors and network domains inhibits the speed and
effectiveness of DDoS attack mitigation. This document describes the
required characteristics of protocols enabling requests for DDoS
attack mitigation, reducing attack impact and leading to more
efficient defensive strategies.
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 form any defensive action takes. DOTS supplements calls
for help with pertinent details about the detected attack, allowing
entities participating in DOTS to form ad hoc, adaptive alliances
against DDoS attacks as described in the DOTS use cases
[I-D.ietf-dots-use-cases]. The requirements in this document are
derived from those 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 are directed at a target on a
network. DDoS attacks are intended to cause a negative impact on
the availability of servers, services, applications, 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.
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Countermeasure: An action or set of actions taken to recognize and
filter out DDoS attack traffic while passing legitimate traffic to
the attack target.
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. For
the purposes of this document, this entity is a black box capable
of mitigation, making no assumptions about availability or design
of countermeasures, nor about the programmable interface(s)
between this entity and other network elements. The mitigator and
invoked DOTS server 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. A DOTS server may also be
colocated with a mitigator.
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 a DOTS server and a DOTS client,
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 to 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 two DOTS agents characterized by
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resilience 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 between DOTS agents, used to indicate the client's
need for mitigation, as well as to convey the status of any
requested mitigation.
Heartbeat: A message transmitted between DOTS agents over the signal
channel, used as a keep-alive and to measure peer health.
Data channel: A secure communication layer between two DOTS agents
used for infrequent 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 filter list of addresses, prefixes, and/or other
identifiers indicating sources from which traffic should be
blocked, regardless of traffic content.
Whitelist: A list of addresses, prefixes, and/or other identifiers
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.
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The DOTS protocol must at a minimum make it possible for a DOTS
client to request a mitigator's 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
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. Further multi-homing considerations are out
of scope.
Regular feedback between DOTS clients and DOTS servers supplement the
defensive alliance by maintaining a common understanding of the DOTS
agents' health and activity. Bidirectional communication between
DOTS clients and DOTS servers is therefore critical.
DOTS protocol implementations face competing operational goals when
maintaining this bidirectional communication stream. On the one
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. The DOTS solution indeed must be viable especially in their
absence.
On the other hand, DOTS must include protections ensuring message
confidentiality, integrity and authenticity to keep the protocol from
becoming another vector for the very attacks it's meant to help fight
off. DOTS clients must be able to authenticate DOTS servers, and
vice versa, to avoid exposing new attack surfaces when deploying
DOTS; specifically, to prevent DDoS mitigation in response to DOTS
signaling from becoming a new form of attack. In order to provide
this level of protection, DOTS agents must have a way to negotiate
and agree upon the terms of protocol security. Attacks against the
transport protocol should not offer a means of attack against the
message confidentiality, integrity and authenticity.
The DOTS server and client must also have some common method of
defining the scope of any mitigation performed by a mitigator, as
well as making adjustments to other commonly configurable features,
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such as targeted port numbers, exchanging black- and white-lists, and
so on.
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 imposed 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,
DOTS signals SHOULD be conveyed over a transport not susceptible
to Head of Line Blocking.
GEN-003 Bidirectionality: To support peer health detection, to
maintain an open signal channel, and to 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.
GEN-004 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.
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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
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 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 is not specified, 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
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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
server knows the session is still alive. DOTS servers SHOULD
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-004 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 MAY
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-005 Mitigation Requests and Status: Authorized DOTS clients MUST
be able to request scoped mitigation from DOTS servers. DOTS
servers MUST send mitigation request status in response to granted
DOTS clients requests for mitigation. 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
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DOTS clients MAY take these metrics into account when determining
whether to ask the DOTS server to cease mitigation.
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. For example, if there is a
financial relationship between the DOTS client and server domains,
the DOTS client ceases incurring cost at this point.
SIG-006 Mitigation Lifetime: DOTS servers MUST support mitigation
lifetimes, 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
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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
locally. That value MUST be returned in a reply to the requesting
DOTS client.
SIG-007 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
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discovery. DOTS clients MUST support at least one mechanism to
obtain mitigation scope.
SIG-008 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-009 Conflict Detection and Notification: Multiple DOTS clients
controlled by a single administrative entity may send conflicting
mitigation requests for pools of protected resources 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-010: 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 (BCPs) for NAT traversal.
2.3. Data Channel Requirements
The data channel is intended to be used for bulk data exchanges
between DOTS agents. Unlike the signal channel, which must operate
nominally even when confronted with signal degradation due to
significant packet loss, 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 DOTS data channel protocol MUST be extensible. We anticipate the
data channel will be used for such purposes as configuration or
resource discovery. 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
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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.
The transactional nature of such data exchanges suggests a separate
set of requirements for the data channel, while the potentially
sensitive content sent between DOTS agents requires extra precautions
to ensure data privacy and authenticity.
DATA-001 Reliable transport: Messages sent over the data channel
MUST be delivered reliably, in order sent.
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
industry 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 2.2, 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.
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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
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
above.
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.
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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
The value of DOTS is in standardizing a mechanism to permit elements,
networks or domains under threat of DDoS attack to request aid
mitigating the effects of any such attack. A well-structured DOTS
data model is therefore critical to the development of successful
DOTS protocols.
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
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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.
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 [RFC5405]. 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
DOTS is at risk from three primary attacks:
o DOTS agent impersonation
o Traffic injection
o Signaling blocking
The DOTS protocol MUST be designed for minimal data transfer to
address the blocking risk. Impersonation and traffic injection
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mitigation can be managed through current secure communications best
practices. See Section 2.4 above for a detailed discussion.
5. Contributors
Mohamed Boucadair
Orange
mohamed.boucadair@orange.com
Flemming Andreasen
Cisco Systems, Inc.
fandreas@cisco.com
Dave Dolson
Sandvine
ddolson@sandvine.com
6. Acknowledgments
Thanks to Roman Danyliw and Matt Richardson for careful reading and
feedback.
7. References
7.1. Normative References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
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[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
DOI 10.17487/RFC1191, November 1990,
<https://www.rfc-editor.org/info/rfc1191>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[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, <https://www.rfc-editor.org/info/rfc4632>.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007,
<https://www.rfc-editor.org/info/rfc4821>.
[RFC5405] Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines
for Application Designers", RFC 5405,
DOI 10.17487/RFC5405, November 2008,
<https://www.rfc-editor.org/info/rfc5405>.
[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <https://www.rfc-editor.org/info/rfc8085>.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952,
DOI 10.17487/RFC5952, August 2010,
<https://www.rfc-editor.org/info/rfc5952>.
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7.2. 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,
<https://www.rfc-editor.org/info/rfc3261>.
[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,
<https://www.rfc-editor.org/info/rfc7092>.
[RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet
Denial-of-Service Considerations", RFC 4732,
DOI 10.17487/RFC4732, December 2006,
<https://www.rfc-editor.org/info/rfc4732>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.
Authors' Addresses
Andrew Mortensen
Arbor Networks
2727 S. State St
Ann Arbor, MI 48104
United States
Email: amortensen@arbor.net
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Robert Moskowitz
Huawei
Oak Park, MI 42837
United States
Email: rgm@htt-consult.com
Tirumaleswar Reddy
McAfee, Inc.
Embassy Golf Link Business Park
Bangalore, Karnataka 560071
India
Email: TirumaleswarReddy_Konda@McAfee.com
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