DOTS A. Mortensen
Internet-Draft Arbor Networks, Inc.
Intended status: Informational R. Moskowitz
Expires: April 21, 2016 HTT Consulting
T. Reddy
Cisco Systems, Inc.
October 19, 2015
DDoS Open Threat Signaling Requirements
draft-ietf-dots-requirements-00
Abstract
This document defines the requirements for the DDoS Open Threat
Signaling (DOTS) protocols coordinating attack response against
Distributed Denial of Service (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
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This Internet-Draft will expire on April 21, 2016.
Copyright Notice
Copyright (c) 2015 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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. General Requirements . . . . . . . . . . . . . . . . . . 6
2.2. Operational requirements . . . . . . . . . . . . . . . . 7
2.3. Data channel requirements . . . . . . . . . . . . . . . . 9
2.4. Data model requirements . . . . . . . . . . . . . . . . . 10
3. Congestion Control Considerations . . . . . . . . . . . . . . 10
4. Security Considerations . . . . . . . . . . . . . . . . . . . 10
5. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1. 00 revision . . . . . . . . . . . . . . . . . . . . . . . 11
5.2. Initial revision . . . . . . . . . . . . . . . . . . . . 11
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
6.1. Normative References . . . . . . . . . . . . . . . . . . 11
6.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
1.1. Overview
Distributed Denial of Service (DDoS) attacks continue to plague
networks around the globe, from Tier-1 service providers on down to
enterprises and small businesses. Attack scale and frequency
similarly have continued to increase, thanks to software
vulnerabilities leading to reflection and amplification attacks.
Once staggering attack traffic volume is now the norm, and the impact
of larger-scale attacks attract the attention of international press
agencies.
The higher profile and 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-premise attack prevention 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. Each service offers its own
interface for subscribers to request attack mitigation, tying
subscribers to proprietary implementations while also limiting the
subset of network elements capable of participating in the attack
response. As a result of incompatibility across services, attack
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response may be fragmentary or otherwise incomplete, leaving key
players in the attack path unable to assist in the defense.
There are many ways to respond to an ongoing DDoS attack, some of
them better than others, but the lack of a common method to
coordinate a real-time response across layers and network domains
inhibits the speed and effectiveness of DDoS attack mitigation.
DOTS was formed to address this lack. The DOTS protocols are
therefore not concerned with the form of response, but rather with
communicating the need for a response, supplementing the call for
help with pertinent details about the detected attack. To achieve
this aim, the protocol must permit the DOTS client to request or
withdraw a request for coordinated mitigation; to set the scope of
mitigation, restricted to the client's network space; and to supply
summarized attack information and additional hints the DOTS server
elements can use to increase the accuracy and speed of the attack
response.
The protocol must also continue to operate even in extreme network
conditions. It must be resilient enough to ensure a high probability
of signal delivery in spite of high packet loss rates. As such,
elements should be in regular, bidirectional contact to measure peer
health, provide mitigation-related feedback, and allow for active
mitigation adjustments.
Lastly, the protocol must take care to ensure the confidentiality,
integrity and authenticity of messages passed between peers to
prevent the protocol from being repurposed to contribute to the very
attacks it's meant to deflect.
Drawing on the DOTS use cases [I-D.ietf-dots-use-cases] for
reference, this document details the requirements for protocols
achieving the DOTS goal of standards-based open threat signaling.
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].
The following terms are used to define relationships between
elements, the data they exchange, and methods of communication among
them:
attack telemetry: collected network traffic characteristics defining
the nature of a DDoS attack.
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mitigation: A defensive response against a detected DDoS attack,
performed by an entity in the network path between attack sources
and the attack target, either through inline deployment or some
form of traffic diversion. The form mitigation takes is out of
scope for this document.
mitigator: A network element capable of performing mitigation of a
detected DDoS attack.
DOTS client: A DOTS-aware network element requesting attack response
coordination with another DOTS-aware element, with the expectation
that the remote element is capable of helping fend off the attack
against the client.
DOTS server: A DOTS-aware network element handling and responding to
messages from a DOTS client. The DOTS server MAY enable
mitigation on behalf of the DOTS client, if requested, by
communicating the DOTS client's request to the mitigator and
relaying any mitigator feedback to the client. A DOTS server may
also be a mitigator.
DOTS relay: A DOTS-aware network element positioned between a DOTS
server and a DOTS client. A DOTS relay receives messages from a
DOTS client and relays them to a DOTS server, and similarly passes
messages from the DOTS server to the DOTS client.
DOTS agents: A collective term for DOTS clients, servers and relays.
signal channel: A bidirectional, mutually authenticated
communication layer between DOTS agents characterized by
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 client's need
for mitigation, as well as to convey the status of any requested
mitigation.
heartbeat: A keep-alive message transmitted between DOTS agents over
the signal channel, used to measure peer health. Heartbeat
functionality is not required to be distinct from signal.
client signal: A message sent from a DOTS client to a DOTS server
over the signal channel, possibly traversing a DOTS relay,
indicating the DOTS client's need for mitigation, as well as the
scope of any requested mitigation, optionally including detected
attack telemetry to supplement server-initiated mitigation.
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server signal: A message sent from a DOTS server to a DOTS client
over the signal channel. Note that a server signal is not a
response to client signal, but a DOTS server-initiated status
message sent to the DOTS client, containing information about the
status of any requested mitigation and its efficacy.
data channel: A secure communication layer between client and server
used for infrequent bulk exchange of data not easily or
appropriately communicated through the signal channel under attack
conditions.
blacklist: a list of source addresses or prefixes from which traffic
should be blocked.
whitelist: a list of source addresses or prefixes from which traffic
should always be allowed, regardless of contradictory data gleaned
in a detected attack.
2. Requirements
This section describes the required features and characteristics of
the DOTS protocols. The requirements are informed by the use cases
described in [I-D.ietf-dots-use-cases].
DOTS must at a minimum make it possible for a DOTS client to request
a DOTS server's aid in mounting a coordinated defense against a
detected attack, by signaling inter- or intra-domain using the DOTS
protocol. DOTS clients should similarly be able to withdraw aid
requests arbitrarily. Regular feedback between DOTS client and
server supplement the defensive alliance by maintaining a common
understanding of DOTS peer health and activity. Bidirectional
communication between DOTS client and server is therefore critical.
Yet the DOTS protocol must also work with a set of competing
operational goals. 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) with a given network will tend to contribute to
the robustness demanded by a viable DOTS protocol.
On the other hand, DOTS must have adequate message confidentiality,
integrity and authenticity to keep the protocol from becoming another
vector for the very attacks it's meant to help fight off. The DOTS
client must be authenticated to the DOTS server, and vice versa, for
DOTS to operate safely, meaning the DOTS agents must have a way to
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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 the mitigator, as
well as making adjustments to other commonly configurable features,
such as listen ports, exchanging black- and white-lists, and so on.
Finally, DOTS should provide sufficient extensibility to meet local,
vendor or future needs in coordinated attack defense, although this
consideration is necessarily superseded by the other operational
requirements.
2.1. General Requirements
G-001 Interoperability: DOTS's objective is to develop a standard
mechanism for signaling detected ongoing DDoS attacks. That
objective is unattainable without well-defined specifications for
any protocols or data models emerging from DOTS. All protocols,
data models and interfaces MUST be detailed enough to ensure
interoperable implementations.
G-002 Extensibility: Any protocols or data models developed as part
of DOTS MUST be designed to support future extensions. Provided
they do not undermine the interoperability and backward
compatibility requirements, extensions are a critical part of
keeping DOTS adaptable to changing operational and proprietary
needs to keep pace with evolving DDoS attack methods.
G-003 Resilience: The signaling protocol MUST be designed to
maximize the probability of signal delivery even under the
severely constrained network conditions imposed by the attack
traffic. The protocol SHOULD be resilient, that is, continue
operating despite message loss and out-of-order or redundant
signal delivery.
G-004 Bidirectionality: To support peer health detection, to
maintain an open signal channel, and to increase the probability
of signal delivery during 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.
G-005 Sub-MTU Message Size: To avoid message fragmentation and the
consequently decreased probability of message delivery, signaling
protocol message size MUST be kept under signaling path Maximum
Transmission Unit (MTU), including the byte overhead of any
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encapsulation, transport headers, and transport- or message-level
security.
G-006 Message Integrity: 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, DOTS agents MUST be able to negotiate the terms
and mechanisms of protocol security, subject to the
interoperability and signal message size requirements above.
G-007 Message Replay Protection: In order to prevent a passive
attacker from capturing and replaying old messages, DOTS protocols
MUST provide a method for replay detection, such as including a
timestamp or sequence number in every heartbeat and signal sent
between DOTS agents.
G-008 Bulk Data Exchange: Infrequent bulk data exchange between DOTS
client and server can also significantly augment attack response
coordination, permitting such tasks as population of black- or
white-listed source addresses; address group aliasing; exchange of
incident reports; and other hinting or configuration supplementing
attack response.
As the resilience requirements for DOTS mandate small signal
message size, a separate, secure data channel utilizing an
established reliable protocol SHOULD be used for bulk data
exchange. The mechanism for bulk data exchange is not yet
specified, but the nature of the data involved suggests use of a
reliable, adaptable protocol with established and configurable
conventions for authentication and authorization.
2.2. Operational requirements
OP-001 Use of Common Transports: DOTS MUST operate over common
standardized transport protocols. While the protocol resilience
requirement strongly RECOMMENDS the use of connectionless
protocols, in particular the User Datagram Protocol (UDP)
[RFC0768], use of a standardized, connection-oriented protocol
like the Transmission Control Protocol (TCP) [RFC0793] MAY be
necessary due to network policy or middleware limitations.
OP-002 Peer Mutual Authentication: The client and server MUST
authenticate each other before a DOTS session is considered
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active. 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.
OP-003 Session Health Monitoring: The client and server MUST
regularly send heartbeats to each other after mutual
authentication in order to keep the DOTS session open. A session
MUST be considered active until a client or server explicitly ends
the session, or either DOTS agent fails to receive heartbeats from
the other after a mutually negotiated timeout period has elapsed.
OP-004 Mitigation Capability Opacity: DOTS is a threat signaling
protocol. The server and mitigator MUST NOT make any assumption
about the attack detection, classification, or mitigation
capabilities of the client. While the server and mitigator MAY
take hints from any attack telemetry included in client signals,
the server and mitigator cannot depend on the client for
authoritative attack classification. Similarly, the mitigator
cannot assume the client can or will mitigate attack traffic on
its own.
The client likewise MUST NOT make any assumptions about the
capabilities of the server or mitigator with respect to detection,
classification, and mitigation of DDoS attacks. The form of any
attack response undertaken by the mitigator is not in scope.
OP-005 Mitigation Status: DOTS clients MUST be able to request or
withdraw a request for mitigation from the DOTS server. The DOTS
server MUST acknowledge a DOTS client's request to withdraw from
coordinated attack response in subsequent signals, and MUST cease
mitigation activity as quickly as possible. However, a DOTS
client rapidly toggling active mitigation may result in
undesirable side-effects for the network path, such as route or
DNS flapping. A DOTS server therefore MAY continue mitigating for
a mutually negotiated period after receiving the DOTS client's
request to stop.
A server MAY refuse to engage in coordinated attack response with
a client. To make the status of a client's request clear, the
server MUST indicate in server signals whether client-initiated
mitigation is active. When a client-initiated mitigation is
active, and threat handling details such as mitigation scope and
statistics are available to the server, the server SHOULD include
those details in server signals sent to the client. DOTS clients
SHOULD take mitigation statistics into account when deciding
whether to request the DOTS server cease mitigation.
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OP-006 Mitigation Scope: DOTS clients MUST indicate the desired
address space coverage of any mitigation, for example by using
Classless Internet Domain Routing (CIDR) [RFC1518],[RFC1519]
prefixes, [RFC2373] for IPv6 prefixes, the length/prefix
convention established in the Border Gateway Protocol (BGP)
[RFC4271], or by a prefix group alias agreed upon with the server
through the data channel. If there is additional information
available narrowing the scope of any requested attack response,
such as targeted port range, protocol, or service, clients SHOULD
include that information in client signals.
As an active attack evolves, clients MUST be able to adjust as
necessary the scope of requested mitigation by refining the
address space requiring intervention.
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 despite signal degradation due to
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 data channel should be adaptable and 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 the
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.
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: Transmissions over the data channel may
be transactional, requiring reliable, in-order packet delivery.
DATA-002 Data privacy and integrity: Transmissions over the data
channel may contain 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 Security
Considerations below.) Consequently data sent over the data
channel MUST be encrypted and authenticated using current industry
best practices.
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DATA-003 Mutual authentication: DOTS agents MUST mutually
authenticate each other before data may be exchanged over the data
channel. DOTS agents MAY take additional steps to authorize data
exchange, as in the prefix group example above, before accepting
data over the data channel. The form of authentication and
authorization is unspecified.
DATA-004 Black- and whitelist management: DOTS servers SHOULD
provide methods for DOTS clients to manage black- and white-lists
of source addresses of traffic destined for addresses 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 the DOTS server determines client ownership of address space
is not in scope.
2.4. Data model requirements
TODO
3. Congestion Control Considerations
The DOTS signal channel will not contribute measurably to link
congestion, as the protocol's transmission rate will be negligible
regardless of network conditions. Bulk data transfers are performed
over the data channel, which should use a reliable transport with
built-in congestion control mechanisms, such as TCP.
4. Security Considerations
DOTS is at risk from three primary attacks: DOTS agent impersonation,
traffic injection, and signaling blocking. The DOTS protocol MUST be
designed for minimal data transfer to address the blocking risk.
Impersonation and traffic injection mitigation can be managed through
current secure communications best practices. DOTS is not subject to
anything new in this area. One consideration could be to minimize
the security technologies in use at any one time. The more needed,
the greater the risk of failures coming from assumptions on one
technology providing protection that it does not in the presence of
another technology.
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5. Change Log
5.1. 00 revision
2015-10-15
5.2. Initial revision
2015-09-24 Andrew Mortensen
6. References
6.1. Normative References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI
10.17487/RFC0768, August 1980,
<http://www.rfc-editor.org/info/rfc768>.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
6.2. Informative References
[RFC1518] Rekhter, Y. and T. Li, "An Architecture for IP Address
Allocation with CIDR", RFC 1518, DOI 10.17487/RFC1518,
September 1993, <http://www.rfc-editor.org/info/rfc1518>.
[RFC1519] Fuller, V., Li, T., Yu, J., and K. Varadhan, "Classless
Inter-Domain Routing (CIDR): an Address Assignment and
Aggregation Strategy", RFC 1519, DOI 10.17487/RFC1519,
September 1993, <http://www.rfc-editor.org/info/rfc1519>.
[RFC2373] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, DOI 10.17487/RFC2373, July 1998,
<http://www.rfc-editor.org/info/rfc2373>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI
10.17487/RFC4271, January 2006,
<http://www.rfc-editor.org/info/rfc4271>.
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Authors' Addresses
Andrew Mortensen
Arbor Networks, Inc.
2727 S. State St
Ann Arbor, MI 48104
United States
Email: amortensen@arbor.net
Robert Moskowitz
HTT Consulting
Oak Park, MI 42837
United States
Email: rgm@htt-consult.com
Tirumaleswar Reddy
Cisco Systems, Inc.
Cessna Business Park, Varthur Hobli
Sarjapur Marathalli Outer Ring Road
Bangalore, Karnataka 560103
India
Email: tireddy@cisco.com
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