Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Specification
draft-ietf-dots-rfc8782-bis-08
| Document | Type | Active Internet-Draft (dots WG) | ||
|---|---|---|---|---|
| Authors | Mohamed Boucadair , Jon Shallow , Tirumaleswar Reddy.K | |||
| Last updated | 2021-06-16 (latest revision 2021-06-03) | |||
| Replaces | draft-boucadair-dots-rfc8782-bis | |||
| Stream | Internet Engineering Task Force (IETF) | |||
| Intended RFC status | Proposed Standard | |||
| Formats | plain text xml pdf htmlized bibtex | |||
| Yang Validation | ☯ 0 errors, 0 warnings. | |||
| Reviews | ||||
| Additional Resources | ||||
| Stream | WG state | Submitted to IESG for Publication | ||
| Document shepherd | Valery Smyslov | |||
| Shepherd write-up | Show (last changed 2021-01-15) | |||
| IESG | IESG state | RFC Ed Queue | ||
| Action Holders |
(None)
|
|||
| Consensus Boilerplate | Yes | |||
| Telechat date | ||||
| Responsible AD | Benjamin Kaduk | |||
| Send notices to | valery@smyslov.net | |||
| IANA | IANA review state | IANA OK - Actions Needed | ||
| IANA action state | RFC-Ed-Ack | |||
| RFC Editor | RFC Editor state | EDIT | ||
| Details | ||||
DOTS M. Boucadair, Ed.
Internet-Draft Orange
Obsoletes: 8782 (if approved) J. Shallow
Intended status: Standards Track
Expires: December 5, 2021 T. Reddy.K
McAfee
June 3, 2021
Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal
Channel Specification
draft-ietf-dots-rfc8782-bis-08
Abstract
This document specifies the Distributed Denial-of-Service Open Threat
Signaling (DOTS) signal channel, a protocol for signaling the need
for protection against Distributed Denial-of-Service (DDoS) attacks
to a server capable of enabling network traffic mitigation on behalf
of the requesting client.
A companion document defines the DOTS data channel, a separate
reliable communication layer for DOTS management and configuration
purposes.
This document obsoletes RFC 8782.
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 December 5, 2021.
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Copyright Notice
Copyright (c) 2021 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
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Design Overview . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Backward Compatibility Considerations . . . . . . . . . . 9
4. DOTS Signal Channel: Messages & Behaviors . . . . . . . . . . 10
4.1. DOTS Server(s) Discovery . . . . . . . . . . . . . . . . 10
4.2. CoAP URIs . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3. Happy Eyeballs for DOTS Signal Channel . . . . . . . . . 11
4.4. DOTS Mitigation Methods . . . . . . . . . . . . . . . . . 13
4.4.1. Request Mitigation . . . . . . . . . . . . . . . . . 14
4.4.1.1. Building Mitigation Requests . . . . . . . . . . 14
4.4.1.2. Server-domain DOTS Gateways . . . . . . . . . . . 22
4.4.1.3. Processing Mitigation Requests . . . . . . . . . 24
4.4.2. Retrieve Information Related to a Mitigation . . . . 30
4.4.2.1. DOTS Servers Sending Mitigation Status . . . . . 36
4.4.2.2. DOTS Clients Polling for Mitigation Status . . . 38
4.4.3. Efficacy Update from DOTS Clients . . . . . . . . . . 39
4.4.4. Withdraw a Mitigation . . . . . . . . . . . . . . . . 41
4.5. DOTS Signal Channel Session Configuration . . . . . . . . 42
4.5.1. Discover Configuration Parameters . . . . . . . . . . 44
4.5.2. Convey DOTS Signal Channel Session Configuration . . 48
4.5.3. Configuration Freshness and Notifications . . . . . . 54
4.5.4. Delete DOTS Signal Channel Session Configuration . . 55
4.6. Redirected Signaling . . . . . . . . . . . . . . . . . . 56
4.7. Heartbeat Mechanism . . . . . . . . . . . . . . . . . . . 58
5. DOTS Signal Channel YANG Modules . . . . . . . . . . . . . . 61
5.1. Tree Structure . . . . . . . . . . . . . . . . . . . . . 61
5.2. IANA DOTS Signal Channel YANG Module . . . . . . . . . . 64
5.3. IETF DOTS Signal Channel YANG Module . . . . . . . . . . 68
6. YANG/JSON Mapping Parameters to CBOR . . . . . . . . . . . . 81
7. (D)TLS Protocol Profile and Performance Considerations . . . 85
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7.1. (D)TLS Protocol Profile . . . . . . . . . . . . . . . . . 85
7.2. (D)TLS 1.3 Considerations . . . . . . . . . . . . . . . . 87
7.3. DTLS MTU and Fragmentation . . . . . . . . . . . . . . . 89
8. Mutual Authentication of DOTS Agents & Authorization of DOTS
Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
9. Error Handling . . . . . . . . . . . . . . . . . . . . . . . 91
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 92
10.1. DOTS Signal Channel UDP and TCP Port Number . . . . . . 92
10.2. Well-Known 'dots' URI . . . . . . . . . . . . . . . . . 93
10.3. Media Type Registration . . . . . . . . . . . . . . . . 93
10.4. CoAP Content-Formats Registration . . . . . . . . . . . 94
10.5. CBOR Tag Registration . . . . . . . . . . . . . . . . . 95
10.6. DOTS Signal Channel Protocol Registry . . . . . . . . . 95
10.6.1. DOTS Signal Channel CBOR Key Values Subregistry . . 95
10.6.1.1. Registration Template . . . . . . . . . . . . . 95
10.6.1.2. Update Subregistry Content . . . . . . . . . . . 97
10.6.2. Status Codes Subregistry . . . . . . . . . . . . . . 97
10.6.3. Conflict Status Codes Subregistry . . . . . . . . . 99
10.6.4. Conflict Cause Codes Subregistry . . . . . . . . . . 100
10.6.5. Attack Status Codes Subregistry . . . . . . . . . . 101
10.7. DOTS Signal Channel YANG Modules . . . . . . . . . . . . 102
11. Security Considerations . . . . . . . . . . . . . . . . . . . 104
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 106
12.1. Normative References . . . . . . . . . . . . . . . . . . 106
12.2. Informative References . . . . . . . . . . . . . . . . . 109
Appendix A. Summary of Changes From RFC8782 . . . . . . . . . . 114
Appendix B. CUID Generation . . . . . . . . . . . . . . . . . . 115
Appendix C. Summary of Protocol Recommended/Default Values . . . 115
Appendix D. Acknowledgements . . . . . . . . . . . . . . . . . . 116
D.1. Acknowledgements from RFC8782 . . . . . . . . . . . . . . 116
Appendix E. Contributors . . . . . . . . . . . . . . . . . . . . 116
E.1. Authors of RFC8782 . . . . . . . . . . . . . . . . . . . 116
E.2. Contributors to RFC8782 . . . . . . . . . . . . . . . . . 117
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 118
1. Introduction
A Distributed Denial-of-Service (DDoS) attack is a distributed
attempt to make machines or network resources unavailable to their
intended users. In most cases, sufficient scale for an effective
attack can be achieved by compromising enough end hosts and using
those infected hosts to perpetrate and amplify the attack. The
victim in this attack can be an application server, a host, a router,
a firewall, or an entire network.
Network applications have finite resources like CPU cycles, the
number of processes or threads they can create and use, the maximum
number of simultaneous connections they can handle, the resources
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assigned to the control plane, etc. When processing network traffic,
such applications are supposed to use these resources to provide the
intended functionality in the most efficient manner. However, a DDoS
attacker may be able to prevent an application from performing its
intended task by making the application exhaust its finite resources.
A TCP DDoS SYN flood [RFC4987], for example, is a memory-exhausting
attack while an ACK flood is a CPU-exhausting attack. Attacks on the
link are carried out by sending enough traffic so that the link
becomes congested, thereby likely causing packet loss for legitimate
traffic. Stateful firewalls can also be attacked by sending traffic
that causes the firewall to maintain an excessive number of states
that may jeopardize the firewall's operation overall, in addition to
likely performance impacts. The firewall then runs out of memory,
and it can no longer instantiate the states required to process
legitimate flows. Other possible DDoS attacks are discussed in
[RFC4732].
In many cases, it may not be possible for network administrators to
determine the cause(s) of an attack. They may instead just realize
that certain resources seem to be under attack. This document
defines a lightweight protocol that allows a DOTS client to request
mitigation from one or more DOTS servers for protection against
detected, suspected, or anticipated attacks. This protocol enables
cooperation between DOTS agents to permit a highly automated network
defense that is robust, reliable, and secure. Note that "secure"
means the support of the features defined in Section 2.4 of
[RFC8612].
In typical deployments, the DOTS client belongs to a different
administrative domain than the DOTS server. For example, the DOTS
client is embedded in a firewall protected services owned and
operated by a customer, while the DOTS server is owned and operated
by a different administrative entity (service provider, typically)
providing DDoS mitigation services. The latter might or might not
provide connectivity services to the network hosting the DOTS client.
The DOTS server may or may not be co-located with the DOTS mitigator.
In typical deployments, the DOTS server belongs to the same
administrative domain as the mitigator. The DOTS client can
communicate directly with a DOTS server or indirectly via a DOTS
gateway.
An example of a network diagram that illustrates a deployment of DOTS
agents is shown in Figure 1. In this example, a DOTS server is
operating on the access network. A DOTS client is located on the LAN
(Local Area Network), while a DOTS gateway is embedded in the CPE
(Customer Premises Equipment).
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Network
Resource CPE Router Access Network __________
+-------------+ +--------------+ +-------------+ / \
| | | | | | | Internet |
| DOTS Client +---+ DOTS Gateway +---+ DOTS Server +----+ |
| | | | | | | |
+-------------+ +--------------+ +-------------+ \__________/
Figure 1: Sample DOTS Deployment (1)
DOTS servers can also be reachable over the Internet, as depicted in
Figure 2.
Network DDoS Mitigation
Resource CPE Router _________ Service
+-------------+ +--------------+ / \ +-------------+
| | | | | | | |
| DOTS Client +---+ DOTS Gateway +---+ Internet +---+ DOTS Server |
| | | | | | | |
+-------------+ +--------------+ \_________/ +-------------+
Figure 2: Sample DOTS Deployment (2)
This document adheres to the DOTS architecture [RFC8811]. The
requirements for DOTS signal channel protocol are documented in
[RFC8612]. This document satisfies all the use cases discussed in
[RFC8903].
This document focuses on the DOTS signal channel. This is a
companion document of the DOTS data channel specification [RFC8783]
that defines a configuration and a bulk data exchange mechanism
supporting the DOTS signal channel.
Backward compatibility (including upgrade) considerations are
discussed in Section 3.1.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119][RFC8174] when, and only when, they appear in all
capitals, as shown here.
(D)TLS is used for statements that apply to both Transport Layer
Security [RFC5246] [RFC8446] and Datagram Transport Layer Security
[RFC6347]. Specific terms are used for any statement that applies to
either protocol alone.
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The reader should be familiar with the terms defined in [RFC8612] and
[RFC7252].
The meaning of the symbols in YANG tree diagrams are defined in
[RFC8340] and [RFC8791].
3. Design Overview
The DOTS signal channel is built on top of the Constrained
Application Protocol (CoAP) [RFC7252], a lightweight protocol
originally designed for constrained devices and networks. The many
features of CoAP (expectation of packet loss, support for
asynchronous Non-confirmable messaging, congestion control, small
message overhead limiting the need for fragmentation, use of minimal
resources, and support for (D)TLS) make it a good candidate upon
which to build the DOTS signaling mechanism.
DOTS clients and servers behave as CoAP endpoints. By default, a
DOTS client behaves as a CoAP client and a DOTS server behaves as
CoAP server. Nevertheless, a DOTS client (or server) behaves as a
CoAP server (or client) for specific operations such as DOTS
heartbeat operations (Section 4.7).
The DOTS signal channel is layered on existing standards (see
Figure 3).
+---------------------+
| DOTS Signal Channel |
+---------------------+
| CoAP |
+----------+----------+
| TLS | DTLS |
+----------+----------+
| TCP | UDP |
+----------+----------+
| IP |
+---------------------+
Figure 3: Abstract Layering of DOTS Signal Channel over CoAP over
(D)TLS
In some cases, a DOTS client and server may have a mutual agreement
to use a specific port number, such as by explicit configuration or
dynamic discovery [RFC8973]. Absent such mutual agreement, the DOTS
signal channel MUST run over port number 4646 as defined in
Section 10.1, for both UDP and TCP (that is, the DOTS server listens
on port number 4646). In order to use a distinct port number (as
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opposed to 4646), DOTS clients and servers SHOULD support a
configurable parameter to supply the port number to use.
| Note: The rationale for not using the default port number 5684
| ((D)TLS CoAP) is to avoid the discovery of services and
| resources discussed in [RFC7252] and allow for differentiated
| behaviors in environments where both a DOTS gateway and an
| Internet of Things (IoT) gateway (e.g., Figure 3 of [RFC7452])
| are co-located.
|
| Particularly, the use of a default port number is meant to
| simplify DOTS deployment in scenarios where no explicit IP
| address configuration is required. For example, the use of the
| default router as the DOTS server aims to ease DOTS deployment
| within LANs (in which CPEs embed a DOTS gateway as illustrated
| in Figures 1 and 2) without requiring a sophisticated discovery
| method and configuration tasks within the LAN. It is also
| possible to use anycast addresses for DOTS servers to simplify
| DOTS client configuration, including service discovery. In
| such an anycast-based scenario, a DOTS client initiating a DOTS
| session to the DOTS server anycast address may, for example, be
| (1) redirected to the DOTS server unicast address to be used by
| the DOTS client following the procedure discussed in
| Section 4.6 or (2) relayed to a unicast DOTS server.
The signal channel uses the "coaps" URI scheme defined in Section 6
of [RFC7252] and the "coaps+tcp" URI scheme defined in Section 8.2 of
[RFC8323] to identify DOTS server resources that are accessible using
CoAP over UDP secured with DTLS and CoAP over TCP secured with TLS,
respectively.
The DOTS signal channel can be established between two DOTS agents
prior to or during an attack. The DOTS signal channel is initiated
by the DOTS client. The DOTS client can then negotiate, configure,
and retrieve the DOTS signal channel session behavior with its DOTS
peer (Section 4.5). Once the signal channel is established, the DOTS
agents may periodically send heartbeats to keep the channel active
(Section 4.7). At any time, the DOTS client may send a mitigation
request message (Section 4.4) to a DOTS server over the active signal
channel. While mitigation is active (because of the higher
likelihood of packet loss during a DDoS attack), the DOTS server
periodically sends status messages to the client, including basic
mitigation feedback details. Mitigation remains active until the
DOTS client explicitly terminates mitigation or the mitigation
lifetime expires. Also, the DOTS server may rely on the signal
channel session loss to trigger mitigation for preconfigured
mitigation requests (if any).
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DOTS signaling can use DTLS over UDP and TLS over TCP. Likewise,
DOTS requests may be sent using IPv4 or IPv6 transfer capabilities.
A Happy Eyeballs procedure for the DOTS signal channel is specified
in Section 4.3.
A DOTS client is entitled to access only the resources it creates.
In particular, a DOTS client cannot retrieve data related to
mitigation requests created by other DOTS clients of the same DOTS
client domain.
Messages exchanged between DOTS agents are serialized using Concise
Binary Object Representation (CBOR) [RFC8949], a binary encoding
scheme designed for small code and message size. CBOR-encoded
payloads are used to carry signal channel-specific payload messages
that convey request parameters and response information such as
errors. In order to allow the reusing of data models across
protocols, [RFC7951] specifies the JavaScript Object Notation (JSON)
encoding of YANG-modeled data. A similar effort for CBOR is defined
in [I-D.ietf-core-yang-cbor].
DOTS agents determine that a CBOR data structure is a DOTS signal
channel object from the application context, such as from the port
number assigned to the DOTS signal channel. The other method DOTS
agents use to indicate that a CBOR data structure is a DOTS signal
channel object is the use of the "application/dots+cbor" content type
(Section 10.3).
This document specifies a YANG module for representing DOTS
mitigation scopes, DOTS signal channel session configuration data,
and DOTS redirected signaling (Section 5). All parameters in the
payload of the DOTS signal channel are mapped to CBOR types as
specified in Table 5 (Section 6).
In order to prevent fragmentation, DOTS agents must follow the
recommendations documented in Section 4.6 of [RFC7252]. Refer to
Section 7.3 for more details.
DOTS agents MUST support GET, PUT, and DELETE CoAP methods. The
payload included in CoAP responses with 2.xx Response Codes MUST be
of content type "application/dots+cbor". CoAP responses with 4.xx
and 5.xx error Response Codes MUST include a diagnostic payload
(Section 5.5.2 of [RFC7252]). The diagnostic payload may contain
additional information to aid troubleshooting.
In deployments where multiple DOTS clients are enabled in a single
network and administrative domain (called, DOTS client domain), the
DOTS server may detect conflicting mitigation requests from these
clients. This document does not aim to specify a comprehensive list
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of conditions under which a DOTS server will characterize two
mitigation requests from distinct DOTS clients as conflicting, nor
does it recommend a DOTS server behavior for processing conflicting
mitigation requests. Those considerations are implementation and
deployment specific. Nevertheless, this document specifies the
mechanisms to notify DOTS clients when conflicts occur, including the
conflict cause (Section 4.4).
In deployments where one or more translators (e.g., Traditional NAT
[RFC3022], CGN [RFC6888], NAT64 [RFC6146], NPTv6 [RFC6296]) are
enabled between the client's network and the DOTS server, any DOTS
signal channel messages forwarded to a DOTS server MUST NOT include
internal IP addresses/prefixes and/or port numbers; instead, external
addresses/prefixes and/or port numbers as assigned by the translator
MUST be used. This document does not make any recommendations about
possible translator discovery mechanisms. The following are some
(non-exhaustive) deployment examples that may be considered:
o Port Control Protocol (PCP) [RFC6887] or Session Traversal
Utilities for NAT (STUN) [RFC8489] may be used by the client to
retrieve the external addresses/prefixes and/or port numbers.
Information retrieved by means of PCP or STUN will be used to feed
the DOTS signal channel messages that will be sent to a DOTS
server.
o A DOTS gateway may be co-located with the translator. The DOTS
gateway will need to update the DOTS messages based upon the local
translator's binding table.
3.1. Backward Compatibility Considerations
The main changes to [RFC8782] are listed in Appendix A. These
modifications are made with the constraint to avoid changes to the
mapping table defined in Table 5 of [RFC8782] (see also Section 6 of
the present document).
For both legacy [RFC8782] and implementations that follow the present
specification, a DOTS signal channel attribute will thus have the
same CBOR key value and CBOR major type. The only upgrade that is
required to [RFC8782] implementations is to handle the CBOR key value
range "128-255" as comprehension-optional instead of comprehension-
required. Note that this range is anticipated to be used by the DOTS
telemetry [I-D.ietf-dots-telemetry] in which the following means are
used to prevent message processing failure of a DOTS signal channel
message enriched with telemetry data: (1) DOTS agents use dedicated
(new) path suffixes (Section 5 of [I-D.ietf-dots-telemetry]) and (2)
a DOTS server won't include telemetry attributes in its responses
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unless it is explicitly told to do so by a DOTS client (Section 6.1.2
of [I-D.ietf-dots-telemetry]).
Future DOTS extensions that request a CBOR value in the range
"128-255" MUST support means similar to the aforementioned DOTS
telemetry ones.
4. DOTS Signal Channel: Messages & Behaviors
4.1. DOTS Server(s) Discovery
This document assumes that DOTS clients are provisioned with the
reachability information of their DOTS server(s) using any of a
variety of means (e.g., local configuration or dynamic means such as
DHCP [RFC8973]). The description of such means is out of scope of
this document.
Likewise, it is out of the scope of this document to specify the
behavior to be followed by a DOTS client in order to send DOTS
requests when multiple DOTS servers are provisioned (e.g., contact
all DOTS servers, select one DOTS server among the list). Such
behavior is specified in other documents (e.g.,
[I-D.ietf-dots-multihoming]).
4.2. CoAP URIs
The DOTS server MUST support the use of the path prefix of "/.well-
known/" as defined in [RFC8615] and the registered name of "dots".
Each DOTS operation is denoted by a path suffix that indicates the
intended operation. The operation path (Table 1) is appended to the
path prefix to form the URI used with a CoAP request to perform the
desired DOTS operation.
+-----------------------+----------------+-------------+
| Operation | Operation Path | Details |
+=======================+================+=============+
| Mitigation | /mitigate | Section 4.4 |
+-----------------------+----------------+-------------+
| Session configuration | /config | Section 4.5 |
+-----------------------+----------------+-------------+
| Heartbeat | /hb | Section 4.7 |
+-----------------------+----------------+-------------+
Table 1: Operations and Corresponding URIs
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4.3. Happy Eyeballs for DOTS Signal Channel
[RFC8612] mentions that DOTS agents will have to support both
connectionless and connection-oriented protocols. As such, the DOTS
signal channel is designed to operate with DTLS over UDP and TLS over
TCP. Further, a DOTS client may acquire a list of IPv4 and IPv6
addresses (Section 4.1), each of which can be used to contact the
DOTS server using UDP and TCP. If no list of IPv4 and IPv6 addresses
to contact the DOTS server is configured (or discovered), the DOTS
client adds the IPv4/IPv6 addresses of its default router to the
candidate list to contact the DOTS server.
The following specifies the procedure to follow to select the address
family and the transport protocol for sending DOTS signal channel
messages.
Such a procedure is needed to avoid experiencing long connection
delays. For example, if an IPv4 path to a DOTS server is functional,
but the DOTS server's IPv6 path is nonfunctional, a dual-stack DOTS
client may experience a significant connection delay compared to an
IPv4-only DOTS client in the same network conditions. The other
problem is that if a middlebox between the DOTS client and DOTS
server is configured to block UDP traffic, the DOTS client will fail
to establish a DTLS association with the DOTS server; consequently,
it will have to fall back to TLS over TCP, thereby incurring
significant connection delays.
To overcome these connection setup problems, the DOTS client attempts
to connect to its DOTS server(s) using both IPv6 and IPv4, and it
tries both DTLS over UDP and TLS over TCP following a DOTS Happy
Eyeballs approach. To some extent, this approach is similar to the
Happy Eyeballs mechanism defined in [RFC8305]. The connection
attempts are performed by the DOTS client when it initializes or, in
general, when it has to select an address family and transport to
contact its DOTS server. The results of the Happy Eyeballs procedure
are used by the DOTS client for sending its subsequent messages to
the DOTS server. The differences in behavior with respect to the
Happy Eyeballs mechanism [RFC8305] are listed below:
o The order of preference of the DOTS signal channel address family
and transport protocol (most preferred first) is the following:
UDP over IPv6, UDP over IPv4, TCP over IPv6, and finally TCP over
IPv4. This order adheres to the address preference order
specified in [RFC6724] and the DOTS signal channel preference that
promotes the use of UDP over TCP (to avoid TCP's head of line
blocking).
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o After successfully establishing a connection, the DOTS client MUST
cache information regarding the outcome of each connection attempt
for a specific time period; it uses that information to avoid
thrashing the network with subsequent attempts. The cached
information is flushed when its age exceeds a specific time period
on the order of few minutes (e.g., 10 min). Typically, if the
DOTS client has to reestablish the connection with the same DOTS
server within a few seconds after the Happy Eyeballs mechanism is
completed, caching avoids thrashing the network especially in the
presence of DDoS attack traffic.
o If a DOTS signal channel session is established with TLS (but DTLS
failed), the DOTS client periodically repeats the mechanism to
discover whether DOTS signal channel messages with DTLS over UDP
become available from the DOTS server; this is so the DOTS client
can migrate the DOTS signal channel from TCP to UDP. Such probing
SHOULD NOT be done more frequently than every 24 hours and MUST
NOT be done more frequently than every 5 minutes.
When connection attempts are made during an attack, the DOTS client
SHOULD use a "Connection Attempt Delay" [RFC8305] set to 100 ms.
In Figure 4, the DOTS client proceeds with the connection attempts
following the rules in [RFC8305]. In this example, it is assumed
that the IPv6 path is broken and UDP traffic is dropped by a
middlebox, but this has little impact on the DOTS client because
there is not a long delay before using IPv4 and TCP.
+-----------+ +-----------+
|DOTS Client| |DOTS Server|
+-----------+ +-----------+
| |
T0 |--DTLS ClientHello, IPv6 ---->X |
T1 |--DTLS ClientHello, IPv4 ---->X |
T2 |--TCP SYN, IPv6-------------->X |
T3 |--TCP SYN, IPv4------------------------------------->|
|<-TCP SYNACK-----------------------------------------|
|--TCP ACK------------------------------------------->|
|<------------Establish TLS Session------------------>|
|----------------DOTS signal------------------------->|
| |
Note:
* Retransmission messages are not shown.
* T1-T0=T2-T1=T3-T2= Connection Attempt Delay.
Figure 4: DOTS Happy Eyeballs (Sample Flow)
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A single DOTS signal channel between DOTS agents can be used to
exchange multiple DOTS signal messages. To reduce DOTS client and
DOTS server workload, DOTS clients SHOULD reuse the (D)TLS session.
4.4. DOTS Mitigation Methods
The following methods are used by a DOTS client to request, withdraw,
or retrieve the status of mitigation requests:
PUT: DOTS clients use the PUT method to request mitigation from a
DOTS server (Section 4.4.1). During active mitigation, DOTS
clients may use PUT requests to carry mitigation efficacy
updates to the DOTS server (Section 4.4.3).
GET: DOTS clients may use the GET method to retrieve the list of
its mitigations maintained by a DOTS server (Section 4.4.2)
or to receive asynchronous DOTS server status messages
(Section 4.4.2.1).
DELETE: DOTS clients use the DELETE method to withdraw a request for
mitigation from a DOTS server (Section 4.4.4).
Mitigation request and response messages are marked as Non-
confirmable messages (Section 2.2 of [RFC7252]).
DOTS agents MUST NOT send more than one UDP datagram per round-trip
time (RTT) to the peer DOTS agent on average following the data
transmission guidelines discussed in Section 3.1.3 of [RFC8085].
Requests marked by the DOTS client as Non-confirmable messages are
sent at regular intervals until a response is received from the DOTS
server. If the DOTS client cannot maintain an RTT estimate, it MUST
NOT send more than one Non-confirmable request every 3 seconds, and
SHOULD use an even less aggressive rate whenever possible (case 2 in
Section 3.1.3 of [RFC8085]). Mitigation requests MUST NOT be delayed
because of checks on probing rate (Section 4.7 of [RFC7252]).
JSON encoding of YANG modeled data [RFC7951] is used to illustrate
the various methods defined in the following subsections. Also, the
examples use the Labels defined in Sections 10.6.2, 10.6.3, 10.6.4,
and 10.6.5.
The DOTS client MUST authenticate itself to the DOTS server
(Section 8). The DOTS server MAY use the algorithm presented in
Section 7 of [RFC7589] to derive the DOTS client identity or username
from the client certificate. The DOTS client identity allows the
DOTS server to accept mitigation requests with scopes that the DOTS
client is authorized to manage.
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4.4.1. Request Mitigation
4.4.1.1. Building Mitigation Requests
When a DOTS client requires mitigation for some reason, the DOTS
client uses the CoAP PUT method to send a mitigation request to its
DOTS server(s) (Figures 5 and 6).
If a DOTS client is entitled to solicit the DOTS service, the DOTS
server enables mitigation on behalf of the DOTS client by
communicating the DOTS client's request to a mitigator (which may be
co-located with the DOTS server) and relaying the feedback of the
thus-selected mitigator to the requesting DOTS client.
Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw"
Uri-Path: "mid=123"
Content-Format: "application/dots+cbor"
{
...
}
Figure 5: PUT to Convey DOTS Mitigation Requests
The order of the Uri-Path options is important as it defines the CoAP
resource. In particular, 'mid' MUST follow 'cuid'.
The additional Uri-Path parameters to those defined in Section 4.2
are as follows:
cuid: Stands for Client Unique Identifier. A globally unique
identifier that is meant to prevent collisions among DOTS
clients, especially those from the same domain. It MUST be
generated by DOTS clients.
For the reasons discussed in Appendix B, implementations SHOULD
set 'cuid' using the following procedure: first, the DOTS
client inputs one of the following into the SHA-256 [RFC6234]
cryptographic hash: the DER-encoded ASN.1 representation of the
Subject Public Key Info (SPKI) of its X.509 certificate
[RFC5280], its raw public key [RFC7250], the "Pre-Shared Key
(PSK) identity" it uses in the TLS 1.2 ClientKeyExchange
message, or the "identity" it uses in the "pre_shared_key" TLS
1.3 extension. Then, the output of the cryptographic hash
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algorithm is truncated to 16 bytes; truncation is done by
stripping off the final 16 bytes. The truncated output is
base64url encoded (Section 5 of [RFC4648]) with the two
trailing "=" removed from the encoding, and the resulting value
used as the 'cuid'.
The 'cuid' is intended to be stable when communicating with a
given DOTS server, i.e., the 'cuid' used by a DOTS client
SHOULD NOT change over time. Distinct 'cuid' values MAY be
used by a single DOTS client per DOTS server.
If a DOTS client has to change its 'cuid' for some reason, it
MUST NOT do so when mitigations are still active for the old
'cuid'. The 'cuid' SHOULD be 22 characters to avoid DOTS
signal message fragmentation over UDP. Furthermore, if that
DOTS client created aliases and filtering entries at the DOTS
server by means of the DOTS data channel, it MUST delete all
the entries bound to the old 'cuid' and reinstall them using
the new 'cuid'.
DOTS servers MUST return 4.09 (Conflict) error code to a DOTS
peer to notify that the 'cuid' is already in use by another
DOTS client. Upon receipt of that error code, a new 'cuid'
MUST be generated by the DOTS peer (e.g., using [RFC4122]).
Client-domain DOTS gateways MUST handle 'cuid' collision
directly and it is RECOMMENDED that 'cuid' collision is handled
directly by server-domain DOTS gateways.
DOTS gateways MAY rewrite the 'cuid' used by peer DOTS clients.
Triggers for such rewriting are out of scope.
This is a mandatory Uri-Path parameter.
mid: Identifier for the mitigation request represented with an
integer. This identifier MUST be unique for each mitigation
request bound to the DOTS client, i.e., the 'mid' parameter
value in the mitigation request needs to be unique (per 'cuid'
and DOTS server) relative to the 'mid' parameter values of
active mitigation requests conveyed from the DOTS client to the
DOTS server.
In order to handle out-of-order delivery of mitigation
requests, 'mid' values MUST increase monotonically.
If the 'mid' value has reached 3/4 of (2^(32) - 1) (i.e.,
3221225471) and no attack is detected, the DOTS client MUST
reset 'mid' to 0 to handle 'mid' rollover. If the DOTS client
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maintains mitigation requests with preconfigured scopes, it
MUST recreate them with the 'mid' restarting at 0.
This identifier MUST be generated by the DOTS client.
This is a mandatory Uri-Path parameter.
'cuid' and 'mid' MUST NOT appear in the PUT request message body
(Figure 6). The schema in Figure 6 uses the types defined in
Section 6. Note that this figure (and other similar figures
depicting a schema) are non-normative sketches of the structure of
the message.
{
"ietf-dots-signal-channel:mitigation-scope": {
"scope": [
{
"target-prefix": [
"string"
],
"target-port-range": [
{
"lower-port": number,
"upper-port": number
}
],
"target-protocol": [
number
],
"target-fqdn": [
"string"
],
"target-uri": [
"string"
],
"alias-name": [
"string"
],
"lifetime": number,
"trigger-mitigation": true|false
}
]
}
}
Figure 6: PUT to Convey DOTS Mitigation Requests (Message Body
Schema)
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The parameters in the CBOR body (Figure 6) of the PUT request are
described below:
target-prefix: A list of prefixes identifying resources under
attack. Prefixes are represented using Classless Inter-Domain
Routing (CIDR) notation [RFC4632].
The prefix length must be less than or equal to 32 for IPv4 and
128 for IPv6.
The prefix list MUST NOT include broadcast, loopback, or multicast
addresses. These addresses are considered to be invalid values.
In addition, the DOTS server MUST validate that target prefixes
are within the scope of the DOTS client domain. Other validation
checks may be supported by DOTS servers.
This is an optional attribute.
target-port-range: A list of port numbers bound to resources under
attack.
A port range is defined by two bounds, a lower port number
('lower-port') and an upper port number ('upper-port'). When only
'lower-port' is present, it represents a single port number.
For TCP, UDP, Stream Control Transmission Protocol (SCTP)
[RFC4960], or Datagram Congestion Control Protocol (DCCP)
[RFC4340], a range of ports can be, for example, 0-1023,
1024-65535, or 1024-49151.
This is an optional attribute.
target-protocol: A list of protocols involved in an attack. Values
are integers in the range of 0 to 255. See [IANA-Proto] for
common values.
If 'target-protocol' is not specified, then the request applies to
any protocol.
This is an optional attribute.
target-fqdn: A list of Fully Qualified Domain Names (FQDNs)
identifying resources under attack [RFC8499].
How a name is passed to an underlying name resolution library is
implementation and deployment specific. Nevertheless, once the
name is resolved into one or multiple IP addresses, DOTS servers
MUST apply the same validation checks as those for 'target-
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prefix'. These validation checks are reiterated by DOTS servers
each time a name is passed to an underlying name resolution
library (e.g., upon expiry of DNS TTL).
The use of FQDNs may be suboptimal because:
* It induces both an extra load and increased delays on the DOTS
server to handle and manage DNS resolution requests.
* It does not guarantee that the DOTS server will resolve a name
to the same IP addresses that the DOTS client does.
This is an optional attribute.
target-uri: A list of URIs [RFC3986] identifying resources under
attack.
The same validation checks used for 'target-fqdn' MUST be followed
by DOTS servers to validate a target URI.
This is an optional attribute.
alias-name: A list of aliases of resources for which the mitigation
is requested. Aliases can be created using the DOTS data channel
(Section 6.1 of [RFC8783]), direct configuration, or other means.
An alias is used in subsequent signal channel exchanges to refer
more efficiently to the resources under attack.
This is an optional attribute.
lifetime: Lifetime of the mitigation request in seconds. The
RECOMMENDED lifetime of a mitigation request is 3600 seconds: this
value was chosen to be long enough so that refreshing is not
typically a burden on the DOTS client, while still making the
request expire in a timely manner when the client has unexpectedly
quit. DOTS clients MUST include this parameter in their
mitigation requests.
A lifetime of '0' in a mitigation request is an invalid value.
A lifetime of negative one (-1) indicates indefinite lifetime for
the mitigation request. The DOTS server MAY refuse an indefinite
lifetime, for policy reasons; the granted lifetime value is
returned in the response. DOTS clients MUST be prepared to not be
granted mitigations with indefinite lifetimes.
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The DOTS server MUST always indicate the actual lifetime in the
response and the remaining lifetime in status messages sent to the
DOTS client.
Upon the expiry of the negotiated lifetime (i.e., the remaining
lifetime reaches '0'), and if the request is not refreshed by the
DOTS client, the mitigation request is removed by the DOTS server.
The request can be refreshed by sending the same request again.
This is a mandatory attribute.
trigger-mitigation: If the parameter value is set to 'false', DDoS
mitigation will not be triggered for the mitigation request unless
the DOTS signal channel session is lost.
If the DOTS client ceases to respond to heartbeat messages, the
DOTS server can detect that the DOTS signal channel session is
lost. More details are discussed in Section 4.7.
The default value of the parameter is 'true' (that is, the
mitigation starts immediately). If 'trigger-mitigation' is not
present in a request, this is equivalent to receiving a request
with 'trigger-mitigation' set to 'true'.
This is an optional attribute.
Because of the complexity of handling partial failure cases, this
specification does not allow the inclusion of multiple mitigation
requests in the same PUT request. Concretely, a DOTS client MUST NOT
include multiple entries in the 'scope' array of the same PUT
request.
FQDN and URI mitigation scopes may be thought of as a form of scope
alias, in which the addresses associated with the domain name or URI
(as resolved by the DOTS server) represent the scope of the
mitigation. Particularly, the IP addresses to which the host
subcomponent of authority component of a URI resolves represent the
'target-prefix', the URI scheme represents the 'target-protocol', the
port subcomponent of authority component of a URI represents the
'target-port-range'. If the optional port information is not present
in the authority component, the default port defined for the URI
scheme represents the 'target-port'.
In the PUT request, at least one of the attributes 'target-prefix',
'target-fqdn','target-uri', or 'alias-name' MUST be present.
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Attributes and Uri-Path parameters with empty values MUST NOT be
present in a request as an empty value will render the entire request
invalid.
Figure 7 shows a PUT request example to signal that servers
2001:db8:6401::1 and 2001:db8:6401::2 are receiving attack traffic on
TCP port numbers 80, 8080, and 443. The presence of 'cdid' indicates
that a server-domain DOTS gateway has modified the initial PUT
request sent by the DOTS client. Note that 'cdid' MUST NOT appear in
the PUT request message body.
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Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cdid=7eeaf349529eb55ed50113"
Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw"
Uri-Path: "mid=123"
Content-Format: "application/dots+cbor"
{
"ietf-dots-signal-channel:mitigation-scope": {
"scope": [
{
"target-prefix": [
"2001:db8:6401::1/128",
"2001:db8:6401::2/128"
],
"target-port-range": [
{
"lower-port": 80
},
{
"lower-port": 443
},
{
"lower-port": 8080
}
],
"target-protocol": [
6
],
"lifetime": 3600
}
]
}
}
Figure 7: PUT for DOTS Mitigation Request (An Example)
The corresponding CBOR encoding format for the payload is shown in
Figure 8.
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A1 # map(1)
01 # unsigned(1)
A1 # map(1)
02 # unsigned(2)
81 # array(1)
A4 # map(4)
06 # unsigned(6)
82 # array(2)
74 # text(20)
323030313A6462383A363430313A3A312F313238
74 # text(20)
323030313A6462383A363430313A3A322F313238
07 # unsigned(7)
83 # array(3)
A1 # map(1)
08 # unsigned(8)
18 50 # unsigned(80)
A1 # map(1)
08 # unsigned(8)
19 01BB # unsigned(443)
A1 # map(1)
08 # unsigned(8)
19 1F90 # unsigned(8080)
0A # unsigned(10)
81 # array(1)
06 # unsigned(6)
0E # unsigned(14)
19 0E10 # unsigned(3600)
Figure 8: PUT for DOTS Mitigation Request (CBOR)
4.4.1.2. Server-domain DOTS Gateways
In deployments where server-domain DOTS gateways are enabled,
identity information about the origin source client domain ('cdid')
SHOULD be propagated to the DOTS server. That information is meant
to assist the DOTS server in enforcing some policies such as grouping
DOTS clients that belong to the same DOTS domain, limiting the number
of DOTS requests, and identifying the mitigation scope. These
policies can be enforced per client, per client domain, or both.
Also, the identity information may be used for auditing and debugging
purposes.
Figure 9 shows an example of a request relayed by a server-domain
DOTS gateway.
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Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cdid=7eeaf349529eb55ed50113"
Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw"
Uri-Path: "mid=123"
Content-Format: "application/dots+cbor"
{
...
}
Figure 9: PUT for DOTS Mitigation Request as Relayed by a DOTS
Gateway
A server-domain DOTS gateway SHOULD add the following Uri-Path
parameter:
cdid: Stands for Client Domain Identifier. The 'cdid' is conveyed by
a server-domain DOTS gateway to propagate the source domain
identity from the gateway's client-facing side to the gateway's
server-facing side, and from the gateway's server-facing side
to the DOTS server. 'cdid' may be used by the final DOTS
server for policy enforcement purposes (e.g., enforce a quota
on filtering rules). These policies are deployment specific.
Server-domain DOTS gateways SHOULD support a configuration
option to instruct whether 'cdid' parameter is to be inserted.
In order to accommodate deployments that require enforcing per-
client policies, per-client domain policies, or a combination
thereof, server-domain DOTS gateways instructed to insert the
'cdid' parameter MUST supply the SPKI hash of the DOTS client
X.509 certificate, the DOTS client raw public key, or the hash
of the "PSK identity" in the 'cdid', following the same rules
for generating the hash conveyed in 'cuid', which is then used
by the ultimate DOTS server to determine the corresponding
client's domain. The 'cdid' generated by a server-domain
gateway is likely to be the same as the 'cuid' except the case
in which the DOTS message was relayed by a client-domain DOTS
gateway or the 'cuid' was generated by a rogue DOTS client.
If a DOTS client is provisioned, for example, with distinct
certificates to use to peer with distinct server-domain DOTS
gateways that peer to the same DOTS server, distinct 'cdid'
values may be supplied by the server-domain DOTS gateways to
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the server. The ultimate DOTS server MUST treat those 'cdid'
values as equivalent.
The 'cdid' attribute MUST NOT be generated and included by DOTS
clients.
DOTS servers MUST ignore 'cdid' attributes that are directly
supplied by source DOTS clients or client-domain DOTS gateways.
This implies that first server-domain DOTS gateways MUST strip
'cdid' attributes supplied by DOTS clients. DOTS servers
SHOULD support a configuration parameter to identify DOTS
gateways that are trusted to supply 'cdid' attributes.
Only single-valued 'cdid' are defined in this document. That
is, only the first on-path server-domain DOTS gateway can
insert a 'cdid' value. This specification does not allow
multiple server-domain DOTS gateways, whenever involved in the
path, to insert a 'cdid' value for each server-domain gateway.
This is an optional Uri-Path. When present, 'cdid' MUST be
positioned before 'cuid'.
A DOTS gateway SHOULD add the CoAP Hop-Limit Option [RFC8768].
4.4.1.3. Processing Mitigation Requests
The DOTS server couples the DOTS signal and data channel sessions
using the DOTS client identity and optionally the 'cdid' parameter
value, so the DOTS server can validate whether the aliases conveyed
in the mitigation request were indeed created by the same DOTS client
using the DOTS data channel session. If the aliases were not created
by the DOTS client, the DOTS server MUST return 4.00 (Bad Request) in
the response.
The DOTS server couples the DOTS signal channel sessions using the
DOTS client identity and optionally the 'cdid' parameter value, and
the DOTS server uses 'mid' and 'cuid' Uri-Path parameter values to
detect duplicate mitigation requests. If the mitigation request
contains the 'alias-name' and other parameters identifying the target
resources (such as 'target-prefix', 'target-port-range', 'target-
fqdn', or 'target-uri'), the DOTS server appends the parameter values
associated with the 'alias-name' with the corresponding parameter
values in 'target-prefix', 'target-port-range', 'target-fqdn', or
'target-uri'.
The DOTS server indicates the result of processing the PUT request
using CoAP Response Codes. CoAP 2.xx codes are success. CoAP 4.xx
codes are some sort of invalid requests (client errors). CoAP 5.xx
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codes are returned if the DOTS server is in an error state or is
currently unavailable to provide mitigation in response to the
mitigation request from the DOTS client.
Figure 10 shows an example response to a PUT request that is
successfully processed by a DOTS server (i.e., CoAP 2.xx Response
Codes). This version of the specification forbids 'cuid' and 'cdid'
(if used) to be returned in a response message body.
{
"ietf-dots-signal-channel:mitigation-scope": {
"scope": [
{
"mid": 123,
"lifetime": 3600
}
]
}
}
Figure 10: 2.xx Response Body
If the request is missing a mandatory attribute, does not include
'cuid' or 'mid' Uri-Path options, includes multiple 'scope'
parameters, or contains invalid or unknown parameters, the DOTS
server MUST reply with 4.00 (Bad Request). DOTS agents can safely
ignore comprehension-optional parameters they don't understand
(Section 10.6.1.1).
A DOTS server that receives a mitigation request with a 'lifetime'
set to '0' MUST reply with a 4.00 (Bad Request).
If the DOTS server does not find the 'mid' parameter value conveyed
in the PUT request in its configuration data, it MAY accept the
mitigation request by sending back a 2.01 (Created) response to the
DOTS client; the DOTS server will consequently try to mitigate the
attack. A DOTS server MAY reject mitigation requests when it is near
capacity or needs to rate-limit a particular client, for example.
The relative order of two mitigation requests with the same 'trigger-
mitigation' type from a DOTS client is determined by comparing their
respective 'mid' values. If two mitigation requests with the same
'trigger-mitigation' type have overlapping mitigation scopes, the
mitigation request with the highest numeric 'mid' value will override
the other mitigation request. Two mitigation requests from a DOTS
client have overlapping scopes if there is a common IP address, IP
prefix, FQDN, URI, or alias. To avoid maintaining a long list of
overlapping mitigation requests (i.e., requests with the same
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'trigger-mitigation' type and overlapping scopes) from a DOTS client
and to avoid error-prone provisioning of mitigation requests from a
DOTS client, the overlapped lower numeric 'mid' MUST be automatically
deleted and no longer available at the DOTS server. For example, if
the DOTS server receives a mitigation request that overlaps with an
existing mitigation with a higher numeric 'mid', the DOTS server
rejects the request by returning 4.09 (Conflict) to the DOTS client.
The response MUST include enough information for a DOTS client to
recognize the source of the conflict as described below in the
'conflict-information' subtree (Section 5.1) with only the relevant
nodes listed:
conflict-information: Indicates that a mitigation request is
conflicting with another mitigation request. This attribute has
the following structure:
conflict-cause: Indicates the cause of the conflict. The
following value MUST be returned:
1: Overlapping targets. 'conflict-scope' provides more details
about the conflicting target clauses.
conflict-scope: Characterizes the exact conflict scope. It may
include a list of IP addresses, a list of prefixes, a list of
target protocols, a list of FQDNs, a list of URIs, a list of
aliases, or a 'mid'. A list of port numbers may also be
included if there is a common IP address, IP prefix, FQDN, URI,
or alias.
If the DOTS server receives a mitigation request that overlaps with
an active mitigation request, but both have distinct 'trigger-
mitigation' types, the DOTS server SHOULD deactivate (absent explicit
policy/configuration otherwise) the mitigation request with 'trigger-
mitigation' set to 'false'. Particularly, if the mitigation request
with 'trigger-mitigation' set to 'false' is active, the DOTS server
withdraws the mitigation request (i.e., status code is set to '7' as
defined in Table 3) and transitions the status of the mitigation
request to '8'.
Upon DOTS signal channel session loss with a peer DOTS client, the
DOTS server SHOULD withdraw (absent explicit policy/configuration
otherwise) any active mitigation requests that overlap with
mitigation requests having 'trigger-mitigation' set to 'false' from
that DOTS client, as the loss of the session implicitly activates
these preconfigured mitigation requests, and they take precedence.
Note that the active-but-terminating period is not observed for
mitigations withdrawn at the initiative of the DOTS server.
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DOTS clients may adopt various strategies for setting the scopes of
immediate and preconfigured mitigation requests to avoid potential
conflicts. For example, a DOTS client may tweak preconfigured scopes
so that the scope of any overlapping immediate mitigation request
will be a subset of the preconfigured scopes. Also, if an immediate
mitigation request overlaps with any of the preconfigured scopes, the
DOTS client sets the scope of the overlapping immediate mitigation
request to be a subset of the preconfigured scopes, so as to get a
broad mitigation when the DOTS signal channel collapses and to
maximize the chance of recovery.
If the request conflicts with an existing mitigation request from a
different DOTS client, the DOTS server may return 2.01 (Created) or
4.09 (Conflict) to the requesting DOTS client. If the DOTS server
decides to maintain the new mitigation request, the DOTS server
returns 2.01 (Created) to the requesting DOTS client. If the DOTS
server decides to reject the new mitigation request, the DOTS server
returns 4.09 (Conflict) to the requesting DOTS client. For both 2.01
(Created) and 4.09 (Conflict) responses, the response MUST include
enough information for a DOTS client to recognize the source of the
conflict as described below:
conflict-information: Indicates that a mitigation request is
conflicting with another mitigation request(s) from other DOTS
client(s). This attribute has the following structure:
conflict-status: Indicates the status of a conflicting mitigation
request. The following values are defined:
1: DOTS server has detected conflicting mitigation requests
from different DOTS clients. This mitigation request is
currently inactive until the conflicts are resolved.
Another mitigation request is active.
2: DOTS server has detected conflicting mitigation requests
from different DOTS clients. This mitigation request is
currently active.
3: DOTS server has detected conflicting mitigation requests
from different DOTS clients. All conflicting mitigation
requests are inactive.
conflict-cause: Indicates the cause of the conflict. The
following values are defined:
1: Overlapping targets. 'conflict-scope' provides more details
about the conflicting target clauses.
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2: Conflicts with an existing accept-list. This code is
returned when the DDoS mitigation detects source addresses/
prefixes in the accept-listed ACLs are attacking the
target.
3: CUID Collision. This code is returned when a DOTS client
uses a 'cuid' that is already used by another DOTS client.
This code is an indication that the request has been
rejected and a new request with a new 'cuid' is to be re-
sent by the DOTS client (see the example shown in
Figure 11). Note that 'conflict-status', 'conflict-scope',
and 'retry-timer' MUST NOT be returned in the error
response.
conflict-scope: Characterizes the exact conflict scope. It may
include a list of IP addresses, a list of prefixes, a list of
target protocols, a list of FQDNs, a list of URIs, a list of
aliases, or references to conflicting ACLs (by an 'acl-name',
typically [RFC8783]). A list of port numbers may also be
included if there is a common IP address, IP prefix, FQDN, URI,
or alias.
retry-timer: Indicates, in seconds, the time after which the DOTS
client may reissue the same request. The DOTS server returns
'retry-timer' only to DOTS client(s) for which a mitigation
request is deactivated. Any retransmission of the same
mitigation request before the expiry of this timer is likely to
be rejected by the DOTS server for the same reasons.
The 'retry-timer' SHOULD be equal to the lifetime of the active
mitigation request resulting in the deactivation of the
conflicting mitigation request.
If the DOTS server decides to maintain a state for the
deactivated mitigation request, the DOTS server updates the
lifetime of the deactivated mitigation request to 'retry-timer
+ 45 seconds' (that is, this mitigation request remains
deactivated for the entire duration of 'retry-timer + 45
seconds') so that the DOTS client can refresh the deactivated
mitigation request after 'retry-timer' seconds, but before the
expiry of the lifetime, and check if the conflict is resolved.
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(1) Request with a conflicting 'cuid'
Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw"
Uri-Path: "mid=12"
(2) Message body of the 4.09 (Conflict) response
from the DOTS server
{
"ietf-dots-signal-channel:mitigation-scope": {
"scope": [
{
"conflict-information": {
"conflict-cause": "cuid-collision"
}
}
]
}
}
(3) Request with a new 'cuid'
Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=f30d281ce6b64fc5a0b91e"
Uri-Path: "mid=12"
Figure 11: Example of Generating a New 'cuid'
As an active attack evolves, DOTS clients can adjust the scope of
requested mitigation as necessary, by refining the scope of resources
requiring mitigation. This can be achieved by sending a PUT request
with a new 'mid' value that will override the existing one with
overlapping mitigation scopes.
For a mitigation request to continue beyond the initial negotiated
lifetime, the DOTS client has to refresh the current mitigation
request by sending a new PUT request. This PUT request MUST use the
same 'mid' value, and it MUST repeat all the other parameters as sent
in the original mitigation request apart from a possible change to
the 'lifetime' parameter value. In such a case, the DOTS server MAY
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update the mitigation request by setting the remaining lifetime to
the newly negotiated lifetime, and a 2.04 (Changed) response is
returned to indicate a successful update of the mitigation request.
If this is not the case, the DOTS server MUST reject the request with
a 4.00 (Bad Request).
4.4.2. Retrieve Information Related to a Mitigation
A GET request is used by a DOTS client to retrieve information
(including status) of DOTS mitigations from a DOTS server.
'cuid' is a mandatory Uri-Path parameter for GET requests.
Uri-Path parameters with empty values MUST NOT be present in a
request.
The same considerations for manipulating the 'cdid' parameter by
server-domain DOTS gateways specified in Section 4.4.1 MUST be
followed for GET requests.
The 'c' Uri-Query option is used to control selection of
configuration and non-configuration data nodes. Concretely, the 'c'
(content) parameter and its permitted values defined in Table 2
[I-D.ietf-core-comi] can be used to retrieve non-configuration data
(attack mitigation status), configuration data, or both. The DOTS
server MAY support this optional filtering capability. It can safely
ignore it if not supported. If the DOTS client supports the optional
filtering capability, it SHOULD use "c=n" query (to get back only the
dynamically changing data) or "c=c" query (to get back the static
configuration values) when the DDoS attack is active to limit the
size of the response.
+-------+-----------------------------------------------------+
| Value | Description |
+=======+=====================================================+
| c | Return only configuration descendant data nodes |
+-------+-----------------------------------------------------+
| n | Return only non-configuration descendant data nodes |
+-------+-----------------------------------------------------+
| a | Return all descendant data nodes |
+-------+-----------------------------------------------------+
Table 2: Permitted Values of the 'c' Parameter
The DOTS client can use block-wise transfer [RFC7959] to get the list
of all its mitigations maintained by a DOTS server, it can send a
Block2 Option in a GET request with NUM = 0 to aid in limiting the
size of the response. If the representation of all the active
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mitigation requests associated with the DOTS client does not fit
within a single datagram, the DOTS server MUST use the Block2 Option
with NUM = 0 in the GET response. The Size2 Option may be conveyed
in the response to indicate the total size of the resource
representation. The DOTS client retrieves the rest of the
representation by sending additional GET requests with Block2 Options
containing NUM values greater than zero. The DOTS client MUST adhere
to the block size preferences indicated by the DOTS server in the
response. If the DOTS server uses the Block2 Option in the GET
response, and the response is for a dynamically changing resource
(e.g., "c=n" or "c=a" query), the DOTS server MUST include the ETag
Option in the response. The DOTS client MUST include the same ETag
value in subsequent GET requests to retrieve the rest of the
representation.
The following examples illustrate how a DOTS client retrieves active
mitigation requests from a DOTS server. In particular:
o Figure 12 shows the example of a GET request to retrieve all DOTS
mitigation requests signaled by a DOTS client.
o Figure 13 shows the example of a GET request to retrieve a
specific DOTS mitigation request signaled by a DOTS client. The
configuration data to be reported in the response is formatted in
the same order as it was processed by the DOTS server in the
original mitigation request.
These two examples assume the default of "c=a"; that is, the DOTS
client asks for all data to be reported by the DOTS server.
Header: GET (Code=0.01)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw"
Observe: 0
Figure 12: GET to Retrieve All DOTS Mitigation Requests
Header: GET (Code=0.01)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw"
Uri-Path: "mid=12332"
Observe: 0
Figure 13: GET to Retrieve a Specific DOTS Mitigation Request
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If the DOTS server does not find the 'mid' Uri-Path value conveyed in
the GET request in its configuration data for the requesting DOTS
client, it MUST respond with a 4.04 (Not Found) error Response Code.
Likewise, the same error MUST be returned as a response to a request
to retrieve all mitigation records (i.e., 'mid' Uri-Path is not
defined) of a given DOTS client if the DOTS server does not find any
mitigation record for that DOTS client. As a reminder, a DOTS client
is identified by its identity (e.g., client certificate, 'cuid') and
optionally the 'cdid'.
Figure 14 shows a response example of all active mitigation requests
associated with the DOTS client as maintained by the DOTS server.
The response indicates the mitigation status of each mitigation
request.
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{
"ietf-dots-signal-channel:mitigation-scope": {
"scope": [
{
"mid": 12332,
"mitigation-start": "1507818434",
"target-prefix": [
"2001:db8:6401::1/128",
"2001:db8:6401::2/128"
],
"target-protocol": [
17
],
"lifetime": 1756,
"status": "attack-successfully-mitigated",
"bytes-dropped": "134334555",
"bps-dropped": "43344",
"pkts-dropped": "333334444",
"pps-dropped": "432432"
},
{
"mid": 12333,
"mitigation-start": "1507818393",
"target-prefix": [
"2001:db8:6401::1/128",
"2001:db8:6401::2/128"
],
"target-protocol": [
6
],
"lifetime": 1755,
"status": "attack-stopped",
"bytes-dropped": "0",
"bps-dropped": "0",
"pkts-dropped": "0",
"pps-dropped": "0"
}
]
}
}
Figure 14: Response Body to a GET Request
The mitigation status parameters are described below:
mitigation-start: Mitigation start time is expressed in seconds
relative to 1970-01-01T00:00Z in UTC time (Section 3.4.1 of
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[RFC8949]). The CBOR encoding is modified so that the leading tag
1 (epoch-based date/time) MUST be omitted.
This is a mandatory attribute when an attack mitigation is active.
Particularly, 'mitigation-start' is not returned for a mitigation
with 'status' code set to 8.
lifetime: The remaining lifetime of the mitigation request, in
seconds.
This is a mandatory attribute.
status: Status of attack mitigation. The various possible values of
'status' parameter are explained in Table 3.
This is a mandatory attribute.
bytes-dropped: The total dropped byte count for the mitigation
request since the attack mitigation was triggered. The count
wraps around when it reaches the maximum value of unsigned
integer64.
This is an optional attribute.
bps-dropped: The average number of dropped bytes per second for the
mitigation request since the attack mitigation was triggered.
This average SHOULD be over five-minute intervals (that is,
measuring bytes into five-minute buckets and then averaging these
buckets over the time since the mitigation was triggered).
This is an optional attribute.
pkts-dropped: The total number of dropped packet count for the
mitigation request since the attack mitigation was triggered. The
count wraps around when it reaches the maximum value of unsigned
integer64.
This is an optional attribute.
pps-dropped: The average number of dropped packets per second for
the mitigation request since the attack mitigation was triggered.
This average SHOULD be over five-minute intervals (that is,
measuring packets into five-minute buckets and then averaging
these buckets over the time since the mitigation was triggered).
This is an optional attribute.
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+-----------+----------------------------------------------------+
| Parameter | Description |
| Value | |
+===========+====================================================+
| 1 | Attack mitigation setup is in progress (e.g., |
| | changing the network path to redirect the inbound |
| | traffic to a DOTS mitigator). |
+-----------+----------------------------------------------------+
| 2 | Attack is being successfully mitigated (e.g., |
| | traffic is redirected to a DDoS mitigator and |
| | attack traffic is dropped). |
+-----------+----------------------------------------------------+
| 3 | Attack has stopped and the DOTS client can |
| | withdraw the mitigation request. This status code |
| | will be transmitted for immediate mitigation |
| | requests till the mitigation is withdrawn or the |
| | lifetime expires. For mitigation requests with |
| | preconfigured scopes (i.e., 'trigger-mitigation' |
| | set to 'false'), this status code will be |
| | transmitted four times and then transition to "8". |
+-----------+----------------------------------------------------+
| 4 | Attack has exceeded the mitigation provider |
| | capability. |
+-----------+----------------------------------------------------+
| 5 | DOTS client has withdrawn the mitigation request |
| | and the mitigation is active but terminating. |
+-----------+----------------------------------------------------+
| 6 | Attack mitigation is now terminated. |
+-----------+----------------------------------------------------+
| 7 | Attack mitigation is withdrawn (by the DOTS |
| | server). If a mitigation request with 'trigger- |
| | mitigation' set to 'false' is withdrawn because it |
| | overlaps with an immediate mitigation request, |
| | this status code will be transmitted four times |
| | and then transition to "8" for the mitigation |
| | request with preconfigured scopes. |
+-----------+----------------------------------------------------+
| 8 | Attack mitigation will be triggered for the |
| | mitigation request only when the DOTS signal |
| | channel session is lost. |
+-----------+----------------------------------------------------+
Table 3: Values of 'status' Parameter
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4.4.2.1. DOTS Servers Sending Mitigation Status
The Observe Option defined in [RFC7641] extends the CoAP core
protocol with a mechanism for a CoAP client to "observe" a resource
on a CoAP server: the client retrieves a representation of the
resource and requests this representation be updated by the server as
long as the client is interested in the resource. DOTS
implementations MUST support the Observe Option for both 'mitigate'
and 'config' (Section 4.2).
A DOTS client conveys the Observe Option set to '0' in the GET
request to receive asynchronous notifications of attack mitigation
status from the DOTS server.
Unidirectional mitigation notifications within the bidirectional
signal channel enables asynchronous notifications between the agents.
[RFC7641] indicates that (1) a notification can be sent in a
Confirmable or a Non-confirmable message, and (2) the message type
used is typically application dependent and may be determined by the
server for each notification individually. For the DOTS server
application, the message type MUST always be set to Non-confirmable
even if the underlying CoAP library elects a notification to be sent
in a Confirmable message. This overrides the behavior defined in
Section 4.5 of [RFC7641] to send a Confirmable message instead of a
Non-confirmable message at least every 24 hours for the following
reasons: First, the DOTS signal channel uses a heartbeat mechanism to
determine if the DOTS client is alive. Second, Confirmable messages
are not suitable during an attack.
Due to the higher likelihood of packet loss during a DDoS attack, the
DOTS server periodically sends attack mitigation status to the DOTS
client and also notifies the DOTS client whenever the status of the
attack mitigation changes. If the DOTS server cannot maintain an RTT
estimate, it MUST NOT send more than one asynchronous notification
every 3 seconds, and SHOULD use an even less aggressive rate whenever
possible (case 2 in Section 3.1.3 of [RFC8085]).
When conflicting requests are detected, the DOTS server enforces the
corresponding policy (e.g., accept all requests, reject all requests,
accept only one request but reject all the others). It is assumed
that this policy is supplied by the DOTS server administrator or that
it is a default behavior of the DOTS server implementation. Then,
the DOTS server sends a notification message(s) to the DOTS client(s)
at the origin of the conflict (refer to the conflict parameters
defined in Section 4.4.1). A conflict notification message includes
information about the conflict cause, scope, and the status of the
mitigation request(s). For example:
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o A notification message with 'status' code set to '7 (Attack
mitigation is withdrawn)' and 'conflict-status' set to '1' is sent
to a DOTS client to indicate that an active mitigation request is
deactivated because a conflict is detected.
o A notification message with 'status' code set to '1 (Attack
mitigation is in progress)' and 'conflict-status' set to '2' is
sent to a DOTS client to indicate that this mitigation request is
in progress, but a conflict is detected.
Upon receipt of a conflict notification message indicating that a
mitigation request is deactivated because of a conflict, a DOTS
client MUST NOT resend the same mitigation request before the expiry
of 'retry-timer'. It is also recommended that DOTS clients support
the means to alert administrators about mitigation conflicts.
A DOTS client that is no longer interested in receiving notifications
from the DOTS server can simply "forget" the observation. When the
DOTS server sends the next notification, the DOTS client will not
recognize the token in the message and, thus, will return a Reset
message. This causes the DOTS server to remove the associated entry.
Alternatively, the DOTS client can explicitly de-register itself by
issuing a GET request that has the Token field set to the token of
the observation to be canceled and includes an Observe Option with
the value set to '1' (de-register). The latter is more deterministic
and, thus, is RECOMMENDED.
Figure 15 shows an example of a DOTS client requesting a DOTS server
to send notifications related to a mitigation request. Note that for
mitigations with preconfigured scopes (i.e., 'trigger-mitigation' set
to 'false'), the state will need to transition from 3 (attack-
stopped) to 8 (attack-mitigation-signal-loss).
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+-----------+ +-----------+
|DOTS Client| |DOTS Server|
+-----------+ +-----------+
| |
| GET /<mid> |
| Token: 0x4a | Registration
| Observe: 0 |
+----------------------------------------->|
| |
| 2.05 Content |
| Token: 0x4a | Notification of
| Observe: 12 | the current state
| status: "attack-mitigation-in-progress" |
|<-----------------------------------------+
| |
| 2.05 Content |
| Token: 0x4a | Notification upon
| Observe: 44 | a state change
| status: "attack-successfully-mitigated" |
|<-----------------------------------------+
| |
| 2.05 Content |
| Token: 0x4a | Notification upon
| Observe: 60 | a state change
| status: "attack-stopped" |
|<-----------------------------------------+
| |
...
Figure 15: Notifications of Attack Mitigation Status
4.4.2.2. DOTS Clients Polling for Mitigation Status
The DOTS client can send the GET request at frequent intervals
without the Observe Option to retrieve the configuration data of the
mitigation request and non-configuration data (i.e., the attack
status). DOTS clients MAY be configured with a policy indicating the
frequency of polling DOTS servers to get the mitigation status. This
frequency MUST NOT be more than one UDP datagram per RTT as discussed
in Section 3.1.3 of [RFC8085].
If the DOTS server has been able to mitigate the attack and the
attack has stopped, the DOTS server indicates as such in the status.
In such case, the DOTS client withdraws the mitigation request by
issuing a DELETE request for this mitigation request (Section 4.4.4).
A DOTS client SHOULD react to the status of the attack per the
information sent by the DOTS server rather than performing its own
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detection that the attack has been mitigated. This ensures that the
DOTS client does not withdraw a mitigation request prematurely
because it is possible that the DOTS client does not sense the DDoS
attack on its resources, but the DOTS server could be actively
mitigating the attack because the attack is not completely averted.
4.4.3. Efficacy Update from DOTS Clients
While DDoS mitigation is in progress, due to the likelihood of packet
loss, a DOTS client MAY periodically transmit DOTS mitigation
efficacy updates to the relevant DOTS server. A PUT request is used
to convey the mitigation efficacy update to the DOTS server. This
PUT request is treated as a refresh of the current mitigation.
The 'attack-status' parameter is a mandatory attribute when
performing an efficacy update. The various possible values contained
in the 'attack-status' parameter are described in Table 4.
+-----------+-------------------------------------+
| Parameter | Description |
| Value | |
+===========+=====================================+
| 1 | The DOTS client determines that it |
| | is still under attack. |
+-----------+-------------------------------------+
| 2 | The DOTS client determines that the |
| | attack is successfully mitigated |
| | (e.g., attack traffic is not seen). |
+-----------+-------------------------------------+
Table 4: Values of 'attack-status' Parameter
The PUT request used for the efficacy update MUST include all the
parameters used in the PUT request to carry the DOTS mitigation
request (Section 4.4.1) unchanged apart from the 'lifetime' parameter
value. If this is not the case, the DOTS server MUST reject the
request with a 4.00 (Bad Request).
The If-Match Option (Section 5.10.8.1 of [RFC7252]) with an empty
value is used to make the PUT request conditional on the current
existence of the mitigation request. If UDP is used as transport,
CoAP requests may arrive out of order. For example, the DOTS client
may send a PUT request to convey an efficacy update to the DOTS
server followed by a DELETE request to withdraw the mitigation
request, but the DELETE request arrives at the DOTS server before the
PUT request. To handle out-of-order delivery of requests, if an If-
Match Option is present in the PUT request and the 'mid' in the
request matches a mitigation request from that DOTS client, the
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request is processed by the DOTS server. If no match is found, the
PUT request is silently ignored by the DOTS server.
An example of an efficacy update message, which includes an If-Match
Option with an empty value, is depicted in Figure 16.
Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw"
Uri-Path: "mid=123"
If-Match:
Content-Format: "application/dots+cbor"
{
"ietf-dots-signal-channel:mitigation-scope": {
"scope": [
{
"target-prefix": [
"2001:db8:6401::1/128",
"2001:db8:6401::2/128"
],
"target-port-range": [
{
"lower-port": 80
},
{
"lower-port": 443
},
{
"lower-port": 8080
}
],
"target-protocol": [
6
],
"attack-status": "under-attack"
}
]
}
}
Figure 16: An Example of Efficacy Update
The DOTS server indicates the result of processing a PUT request
using CoAP Response Codes. The Response Code 2.04 (Changed) is
returned if the DOTS server has accepted the mitigation efficacy
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update. The error Response Code 5.03 (Service Unavailable) is
returned if the DOTS server has erred or is incapable of performing
the mitigation. As specified in [RFC7252], 5.03 uses Max-Age Option
to indicate the number of seconds after which to retry.
4.4.4. Withdraw a Mitigation
DELETE requests are used to withdraw DOTS mitigation requests from
DOTS servers (Figure 17).
'cuid' and 'mid' are mandatory Uri-Path parameters for DELETE
requests.
The same considerations for manipulating 'cdid' parameter by DOTS
gateways, as specified in Section 4.4.1, MUST be followed for DELETE
requests. Uri-Path parameters with empty values MUST NOT be present
in a request.
Header: DELETE (Code=0.04)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw"
Uri-Path: "mid=123"
Figure 17: Withdraw a DOTS Mitigation
If the DELETE request does not include 'cuid' and 'mid' parameters,
the DOTS server MUST reply with a 4.00 (Bad Request).
Once the request is validated, the DOTS server immediately
acknowledges a DOTS client's request to withdraw the DOTS mitigation
request using 2.02 (Deleted) Response Code with no response payload.
A 2.02 (Deleted) Response Code is returned even if the 'mid'
parameter value conveyed in the DELETE request does not exist in its
configuration data before the request.
If the DOTS server finds the 'mid' parameter value conveyed in the
DELETE request in its configuration data for the DOTS client, then to
protect against route or DNS flapping caused by a DOTS client rapidly
removing a mitigation, and to dampen the effect of oscillating
attacks, the DOTS server MAY allow mitigation to continue for a
limited period after acknowledging a DOTS client's withdrawal of a
mitigation request. During this period, the DOTS server status
messages SHOULD indicate that mitigation is active but terminating
(Section 4.4.2).
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The initial active-but-terminating period SHOULD be sufficiently long
to absorb latency incurred by route propagation. The active-but-
terminating period SHOULD be set by default to 120 seconds. If the
client requests mitigation again before the initial active-but-
terminating period elapses, the DOTS server MAY exponentially
increase (the base of the exponent is 2) the active-but-terminating
period up to a maximum of 300 seconds (5 minutes).
Once the active-but-terminating period elapses, the DOTS server MUST
treat the mitigation as terminated.
If a mitigation is triggered due to a signal channel loss, the DOTS
server relies upon normal triggers to stop that mitigation
(typically, receipt of a valid DELETE request, expiry of the
mitigation lifetime, or scrubbing the traffic to the attack target).
In particular, the DOTS server MUST NOT consider the signal channel
recovery as a trigger to stop the mitigation.
4.5. DOTS Signal Channel Session Configuration
A DOTS client can negotiate, configure, and retrieve the DOTS signal
channel session behavior with its DOTS peers. The DOTS signal
channel can be used, for example, to configure the following:
a. Heartbeat interval ('heartbeat-interval'): DOTS agents regularly
send heartbeats to each other after mutual authentication is
successfully completed in order to keep the DOTS signal channel
open. Heartbeat messages are exchanged between DOTS agents every
'heartbeat-interval' seconds to detect the current status of the
DOTS signal channel session.
b. Missing heartbeats allowed ('missing-hb-allowed'): This variable
indicates the maximum number of consecutive heartbeat messages
for which a DOTS agent did not receive a response before
concluding that the session is disconnected or defunct.
c. Acceptable probing rate ('probing-rate'): This parameter
indicates the average data rate that must not be exceeded by a
DOTS agent in sending to a peer DOTS agent that does not respond.
d. Acceptable signal loss ratio: Maximum retransmissions ('max-
retransmit'), retransmission timeout value ('ack-timeout'), and
other message transmission parameters for Confirmable messages
over the DOTS signal channel.
When the DOTS signal channel is established over a reliable transport
(e.g., TCP), there is no need for the reliability mechanisms provided
by CoAP over UDP since the underlying TCP connection provides
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retransmissions and deduplication [RFC8323]. CoAP over reliable
transports does not support Confirmable or Non-confirmable message
types. As such, the transmission-related parameters ('missing-hb-
allowed' and acceptable signal loss ratio) are negotiated only for
DOTS over unreliable transports.
The same or distinct configuration sets may be used during times when
a mitigation is active ('mitigating-config') and when no mitigation
is active ('idle-config'). This is particularly useful for DOTS
servers that might want to reduce heartbeat frequency or cease
heartbeat exchanges when an active DOTS client has not requested
mitigation. If distinct configurations are used, DOTS agents MUST
follow the appropriate configuration set as a function of the
mitigation activity (e.g., if no mitigation request is active (also
referred to as 'idle' time), values related to 'idle-config' must be
followed). Additionally, DOTS agents MUST automatically switch to
the other configuration upon a change in the mitigation activity
(e.g., if an attack mitigation is launched after an 'idle' time, the
DOTS agent switches from values related to 'idle-config' to values
related to 'mitigating-config').
CoAP requests and responses are indicated for reliable delivery by
marking them as Confirmable messages. DOTS signal channel session
configuration requests and responses are marked as Confirmable
messages. As explained in Section 2.1 of [RFC7252], a Confirmable
message is retransmitted using a default timeout and exponential
backoff between retransmissions, until the DOTS server sends an
Acknowledgement message (ACK) with the same Message ID conveyed from
the DOTS client.
Message transmission parameters are defined in Section 4.8 of
[RFC7252]. The DOTS server can either piggyback the response in the
Acknowledgement message or, if the DOTS server cannot respond
immediately to a request carried in a Confirmable message, it simply
responds with an Empty Acknowledgement message so that the DOTS
client can stop retransmitting the request. Empty Acknowledgement
messages are explained in Section 2.2 of [RFC7252]. When the
response is ready, the server sends it in a new Confirmable message,
which, in turn, needs to be acknowledged by the DOTS client (see
Sections 5.2.1 and 5.2.2 of [RFC7252]). Requests and responses
exchanged between DOTS agents during 'idle' time, except heartbeat
messages, are marked as Confirmable messages.
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| Implementation Note: A DOTS client that receives a response in
| a Confirmable message may want to clean up the message state
| right after sending the ACK. If that ACK is lost and the DOTS
| server retransmits the Confirmable message, the DOTS client may
| no longer have any state that would help it correlate this
| response: from the DOTS client's standpoint, the retransmission
| message is unexpected. The DOTS client will send a Reset
| message so it does not receive any more retransmissions. This
| behavior is normal and not an indication of an error (see
| Section 5.3.2 of [RFC7252] for more details).
4.5.1. Discover Configuration Parameters
A GET request is used to obtain acceptable (e.g., minimum and maximum
values) and current configuration parameters on the DOTS server for
DOTS signal channel session configuration. This procedure occurs
between a DOTS client and its immediate peer DOTS server. As such,
this GET request MUST NOT be relayed by a DOTS gateway.
Figure 18 shows how to obtain configuration parameters that the DOTS
server will find acceptable.
Header: GET (Code=0.01)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "config"
Figure 18: GET to Retrieve Configuration
The DOTS server in the 2.05 (Content) response conveys the current,
minimum, and maximum attribute values acceptable by the DOTS server
(Figure 19).
{
"ietf-dots-signal-channel:signal-config": {
"mitigating-config": {
"heartbeat-interval": {
"max-value": number,
"min-value": number,
"current-value": number
},
"missing-hb-allowed": {
"max-value": number,
"min-value": number,
"current-value": number
},
"probing-rate": {
"max-value": number,
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"min-value": number,
"current-value": number
},
"max-retransmit": {
"max-value": number,
"min-value": number,
"current-value": number
},
"ack-timeout": {
"max-value-decimal": "string",
"min-value-decimal": "string",
"current-value-decimal": "string"
},
"ack-random-factor": {
"max-value-decimal": "string",
"min-value-decimal": "string",
"current-value-decimal": "string"
}
},
"idle-config": {
"heartbeat-interval": {
"max-value": number,
"min-value": number,
"current-value": number
},
"missing-hb-allowed": {
"max-value": number,
"min-value": number,
"current-value": number
},
"probing-rate": {
"max-value": number,
"min-value": number,
"current-value": number
},
"max-retransmit": {
"max-value": number,
"min-value": number,
"current-value": number
},
"ack-timeout": {
"max-value-decimal": "string",
"min-value-decimal": "string",
"current-value-decimal": "string"
},
"ack-random-factor": {
"max-value-decimal": "string",
"min-value-decimal": "string",
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"current-value-decimal": "string"
}
}
}
}
Figure 19: GET Configuration Response Body Schema
The parameters in Figure 19 are described below:
mitigating-config: Set of configuration parameters to use when a
mitigation is active. The following parameters may be included:
heartbeat-interval: Time interval in seconds between two
consecutive heartbeat messages.
'0' is used to disable the heartbeat mechanism.
This is an optional attribute.
missing-hb-allowed: Maximum number of consecutive heartbeat
messages for which the DOTS agent did not receive a response
before concluding that the session is disconnected.
This is an optional attribute.
probing-rate: The average data rate, in bytes/second, that must
not be exceeded by a DOTS agent in sending to a peer DOTS agent
that does not respond (referred to as PROBING_RATE parameter in
CoAP).
This is an optional attribute.
max-retransmit: Maximum number of retransmissions for a message
(referred to as MAX_RETRANSMIT parameter in CoAP).
This is an optional attribute.
ack-timeout: Timeout value in seconds used to calculate the
initial retransmission timeout value (referred to as
ACK_TIMEOUT parameter in CoAP).
This is an optional attribute.
ack-random-factor: Random factor used to influence the timing of
retransmissions (referred to as ACK_RANDOM_FACTOR parameter in
CoAP).
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This is an optional attribute.
idle-config: Set of configuration parameters to use when no
mitigation is active. This attribute has the same structure as
'mitigating-config'.
Figure 20 shows an example of acceptable and current configuration
parameters on a DOTS server for DOTS signal channel session
configuration. The same acceptable configuration is used during
mitigation and idle times.
{
"ietf-dots-signal-channel:signal-config": {
"mitigating-config": {
"heartbeat-interval": {
"max-value": 240,
"min-value": 15,
"current-value": 30
},
"missing-hb-allowed": {
"max-value": 20,
"min-value": 3,
"current-value": 15
},
"probing-rate": {
"max-value": 20,
"min-value": 5,
"current-value": 15
},
"max-retransmit": {
"max-value": 15,
"min-value": 2,
"current-value": 3
},
"ack-timeout": {
"max-value-decimal": "30.00",
"min-value-decimal": "1.00",
"current-value-decimal": "2.00"
},
"ack-random-factor": {
"max-value-decimal": "4.00",
"min-value-decimal": "1.10",
"current-value-decimal": "1.50"
}
},
"idle-config": {
"heartbeat-interval": {
"max-value": 240,
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"min-value": 15,
"current-value": 30
},
"missing-hb-allowed": {
"max-value": 20,
"min-value": 3,
"current-value": 15
},
"probing-rate": {
"max-value": 20,
"min-value": 5,
"current-value": 15
},
"max-retransmit": {
"max-value": 15,
"min-value": 2,
"current-value": 3
},
"ack-timeout": {
"max-value-decimal": "30.00",
"min-value-decimal": "1.00",
"current-value-decimal": "2.00"
},
"ack-random-factor": {
"max-value-decimal": "4.00",
"min-value-decimal": "1.10",
"current-value-decimal": "1.50"
}
}
}
}
Figure 20: Example of a Configuration Response Body
4.5.2. Convey DOTS Signal Channel Session Configuration
A PUT request (Figures 21 and 22) is used to convey the configuration
parameters for the signal channel (e.g., heartbeat interval, maximum
retransmissions). Message transmission parameters for CoAP are
defined in Section 4.8 of [RFC7252]. The RECOMMENDED values of
transmission parameter values are 'ack-timeout' (2 seconds), 'max-
retransmit' (3), and 'ack-random-factor' (1.5). In addition to those
parameters, the RECOMMENDED specific DOTS transmission parameter
values are 'heartbeat-interval' (30 seconds) and 'missing-hb-allowed'
(15).
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| Note: 'heartbeat-interval' should be tweaked to also assist
| DOTS messages for NAT traversal (SIG-011 of [RFC8612]).
| According to [RFC8085], heartbeat messages must not be sent
| more frequently than once every 15 seconds and should use
| longer intervals when possible. Furthermore, [RFC4787]
| recommends that NATs use a state timeout of 2 minutes or
| longer, but experience shows that sending packets every 15 to
| 30 seconds is necessary to prevent the majority of middleboxes
| from losing state for UDP flows. From that standpoint, the
| RECOMMENDED minimum 'heartbeat-interval' is 15 seconds and the
| RECOMMENDED maximum 'heartbeat-interval' is 240 seconds. The
| recommended value of 30 seconds is selected to anticipate the
| expiry of NAT state.
|
| A 'heartbeat-interval' of 30 seconds may be considered to be
| too chatty in some deployments. For such deployments, DOTS
| agents may negotiate longer 'heartbeat-interval' values to
| prevent any network overload with too frequent heartbeats.
|
| Different heartbeat intervals can be defined for 'mitigating-
| config' and 'idle-config' to reduce being too chatty during
| idle times. If there is an on-path translator between the DOTS
| client (standalone or part of a DOTS gateway) and the DOTS
| server, the 'mitigating-config' 'heartbeat-interval' has to be
| smaller than the translator session timeout. It is recommended
| that the 'idle-config' 'heartbeat-interval' also be smaller
| than the translator session timeout to prevent translator
| traversal issues or that it be disabled entirely. Means to
| discover the lifetime assigned by a translator are out of
| scope.
|
| Given that the size of the heartbeat request cannot exceed
| ('heartbeat-interval' * 'probing-rate') bytes, 'probing-rate'
| should be set appropriately to avoid slowing down heartbeat
| exchanges. For example, 'probing-rate' may be set to 2 *
| ("size of encrypted DOTS heartbeat request"/'heartbeat-
| interval') or (("size of encrypted DOTS heartbeat request" +
| "average size of an encrypted mitigation request")/'heartbeat-
| interval'). Absent any explicit configuration or inability to
| dynamically adjust 'probing-rate' values (Section 4.8.1 of
| [RFC7252]), DOTS agents use 5 bytes/second as a default
| 'probing-rate' value.
If the DOTS agent wishes to change the default values of message
transmission parameters, it SHOULD follow the guidance given in
Section 4.8.1 of [RFC7252]. The DOTS agents MUST use the negotiated
values for message transmission parameters and default values for
non-negotiated message transmission parameters.
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The signal channel session configuration is applicable to a single
DOTS signal channel session between DOTS agents, so the 'cuid' Uri-
Path MUST NOT be used.
Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "config"
Uri-Path: "sid=123"
Content-Format: "application/dots+cbor"
{
...
}
Figure 21: PUT to Convey the DOTS Signal Channel Session
Configuration Data
The additional Uri-Path parameter to those defined in Table 1 is as
follows:
sid: Session Identifier is an identifier for the DOTS signal channel
session configuration data represented as an integer. This
identifier MUST be generated by DOTS clients. 'sid' values MUST
increase monotonically (when a new PUT is generated by a DOTS
client to convey the configuration parameters for the signal
channel).
This is a mandatory attribute.
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{
"ietf-dots-signal-channel:signal-config": {
"mitigating-config": {
"heartbeat-interval": {
"current-value": number
},
"missing-hb-allowed": {
"current-value": number
},
"probing-rate": {
"current-value": number
},
"max-retransmit": {
"current-value": number
},
"ack-timeout": {
"current-value-decimal": "string"
},
"ack-random-factor": {
"current-value-decimal": "string"
}
},
"idle-config": {
"heartbeat-interval": {
"current-value": number
},
"missing-hb-allowed": {
"current-value": number
},
"probing-rate": {
"current-value": number
},
"max-retransmit": {
"current-value": number
},
"ack-timeout": {
"current-value-decimal": "string"
},
"ack-random-factor": {
"current-value-decimal": "string"
}
}
}
}
Figure 22: PUT to Convey the DOTS Signal Channel Session
Configuration Data (Message Body Schema)
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The meaning of the parameters in the CBOR body (Figure 22) is defined
in Section 4.5.1.
At least one of the attributes 'heartbeat-interval', 'missing-hb-
allowed', 'probing-rate', 'max-retransmit', 'ack-timeout', and 'ack-
random-factor' MUST be present in the PUT request. Note that
'heartbeat-interval', 'missing-hb-allowed', 'probing-rate', 'max-
retransmit', 'ack-timeout', and 'ack-random-factor', if present, do
not need to be provided for both 'mitigating-config', and 'idle-
config' in a PUT request. A request does not need to include both
'mitigating-config' and 'idle-config' attributes.
The PUT request with a higher numeric 'sid' value overrides the DOTS
signal channel session configuration data installed by a PUT request
with a lower numeric 'sid' value. That is, the configuration
parameters that are included in the PUT request with a higher numeric
'sid' value will be used instead of the DOTS server's defaults. To
avoid maintaining a long list of 'sid' requests from a DOTS client,
the lower numeric 'sid' MUST be automatically deleted and no longer
available at the DOTS server.
Figure 23 shows a PUT request example to convey the configuration
parameters for the DOTS signal channel. In this example, the
heartbeat mechanism is disabled when no mitigation is active, while
the heartbeat interval is set to '30' when a mitigation is active.
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Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "config"
Uri-Path: "sid=123"
Content-Format: "application/dots+cbor"
{
"ietf-dots-signal-channel:signal-config": {
"mitigating-config": {
"heartbeat-interval": {
"current-value": 30
},
"missing-hb-allowed": {
"current-value": 15
},
"probing-rate": {
"current-value": 15
},
"max-retransmit": {
"current-value": 3
},
"ack-timeout": {
"current-value-decimal": "2.00"
},
"ack-random-factor": {
"current-value-decimal": "1.50"
}
},
"idle-config": {
"heartbeat-interval": {
"current-value": 0
},
"max-retransmit": {
"current-value": 3
},
"ack-timeout": {
"current-value-decimal": "2.00"
},
"ack-random-factor": {
"current-value-decimal": "1.50"
}
}
}
}
Figure 23: PUT to Convey the Configuration Parameters
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The DOTS server indicates the result of processing the PUT request
using CoAP Response Codes:
o If the request is missing a mandatory attribute, does not include
a 'sid' Uri-Path, or contains one or more invalid or unknown
parameters, 4.00 (Bad Request) MUST be returned in the response.
o If the DOTS server does not find the 'sid' parameter value
conveyed in the PUT request in its configuration data and if the
DOTS server has accepted the configuration parameters, then a
Response Code 2.01 (Created) MUST be returned in the response.
o If the DOTS server finds the 'sid' parameter value conveyed in the
PUT request in its configuration data and if the DOTS server has
accepted the updated configuration parameters, 2.04 (Changed) MUST
be returned in the response.
o If any of the 'heartbeat-interval', 'missing-hb-allowed',
'probing-rate', 'max-retransmit', 'target-protocol', 'ack-
timeout', and 'ack-random-factor' attribute values are not
acceptable to the DOTS server, 4.22 (Unprocessable Entity) MUST be
returned in the response. Upon receipt of this error code, the
DOTS client SHOULD retrieve the maximum and minimum attribute
values acceptable to the DOTS server (Section 4.5.1).
The DOTS client may retry and send the PUT request with updated
attribute values acceptable to the DOTS server.
A DOTS client may issue a GET message for 'config' with a 'sid' Uri-
Path parameter to retrieve the negotiated configuration. The
response does not need to include 'sid' in its message body.
4.5.3. Configuration Freshness and Notifications
Max-Age Option (Section 5.10.5 of [RFC7252]) SHOULD be returned by a
DOTS server to associate a validity time with a configuration it
sends. This feature forces the client to retrieve the updated
configuration data if a change occurs at the DOTS server side. For
example, the new configuration may instruct a DOTS client to cease
heartbeats or reduce heartbeat frequency.
It is NOT RECOMMENDED to return a Max-Age Option set to 0.
Returning a Max-Age Option set to 2^(32)-1 is equivalent to
associating an infinite lifetime with the configuration.
If a non-zero value of Max-Age Option is received by a DOTS client,
it MUST issue a GET request with a 'sid' Uri-Path parameter to
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retrieve the current and acceptable configuration before the expiry
of the value enclosed in the Max-Age Option. This request is
considered by the client and the server to be a means to refresh the
configuration parameters for the signal channel. When a DDoS attack
is active, refresh requests MUST NOT be sent by DOTS clients, and the
DOTS server MUST NOT terminate the (D)TLS session after the expiry of
the value returned in Max-Age Option.
If Max-Age Option is not returned in a response, the DOTS client
initiates GET requests to refresh the configuration parameters each
60 seconds (Section 5.10.5 of [RFC7252]). To prevent such overload,
it is RECOMMENDED that DOTS servers return a Max-Age Option in GET
responses. Considerations related to which value to use and how such
a value is set are implementation and deployment specific.
If an Observe Option set to 0 is included in the configuration
request, the DOTS server sends notifications of any configuration
change (Section 4.2 of [RFC7641]).
If a DOTS server detects that a misbehaving DOTS client does not
contact the DOTS server after the expiry of Max-Age to retrieve the
signal channel configuration data, it MAY terminate the (D)TLS
session. A (D)TLS session is terminated by the receipt of an
authenticated message that closes the connection (e.g., a fatal alert
(Section 6 of [RFC8446])).
4.5.4. Delete DOTS Signal Channel Session Configuration
A DELETE request is used to delete the installed DOTS signal channel
session configuration data (Figure 24).
Header: DELETE (Code=0.04)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "config"
Uri-Path: "sid=123"
Figure 24: Delete Configuration
The DOTS server resets the DOTS signal channel session configuration
back to the default values and acknowledges a DOTS client's request
to remove the DOTS signal channel session configuration using 2.02
(Deleted) Response Code.
Upon bootstrapping or reboot, a DOTS client MAY send a DELETE request
to set the configuration parameters to default values. Such a
request does not include any 'sid'.
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4.6. Redirected Signaling
Redirected DOTS signaling is discussed in detail in Section 3.2.2 of
[RFC8811].
To redirect a DOTS client to an alternative DOTS server, the DOTS
server can return the error Response Code 5.03 (Service Unavailable)
in response to a request from the DOTS client or convey the error
Response Code 5.03 in a unidirectional notification response to the
client.
The DOTS server in the error response conveys the alternate DOTS
server's FQDN, and the alternate DOTS server's IP address(es) values
in the CBOR body (Figure 25).
{
"ietf-dots-signal-channel:redirected-signal": {
"alt-server": "string",
"alt-server-record": [
"string"
]
}
}
Figure 25: Redirected Server Error Response Body Schema
The parameters are described below:
alt-server: FQDN of an alternate DOTS server.
This is a mandatory attribute.
alt-server-record: A list of IP addresses of an alternate DOTS
server.
This is an optional attribute.
The DOTS server returns the Time to Live (TTL) of the alternate DOTS
server in a Max-Age Option. That is, the time interval that the
alternate DOTS server may be cached for use by a DOTS client. A Max-
Age Option set to 2^(32)-1 is equivalent to receiving an infinite
TTL. This value means that the alternate DOTS server is to be used
until the alternate DOTS server redirects the traffic with another
5.03 response that conveys an alternate server's FQDN.
A Max-Age Option set to '0' may be returned for redirecting
mitigation requests. Such a value means that the redirection applies
only for the mitigation request in progress. Returning short TTL in
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a Max-Age Option may adversely impact DOTS clients on slow links.
Returning short values should be avoided under such conditions.
If the alternate DOTS server TTL has expired, the DOTS client MUST
use the DOTS server(s) that was provisioned using means discussed in
Section 4.1. This fallback mechanism is triggered immediately upon
expiry of the TTL, except when a DDoS attack is active.
Requests issued by misbehaving DOTS clients that do not honor the TTL
conveyed in the Max-Age Option or react to explicit redirect messages
MAY be rejected by DOTS servers.
Figure 26 shows a 5.03 response example to convey the DOTS alternate
server 'alt-server.example' together with its IP addresses
2001:db8:6401::1 and 2001:db8:6401::2.
{
"ietf-dots-signal-channel:redirected-signal": {
"alt-server": "alt-server.example",
"alt-server-record": [
"2001:db8:6401::1",
"2001:db8:6401::2"
]
}
}
Figure 26: Example of Redirected Server Error Response Body
When the DOTS client receives a 5.03 response with an alternate
server included, it considers the current request to have failed, but
it SHOULD try resending the request to the alternate DOTS server.
During a DDoS attack, the DNS server may be the target of another
DDoS attack, the alternate DOTS server's IP addresses conveyed in the
5.03 response help the DOTS client skip the DNS lookup of the
alternate DOTS server, at the cost of trusting the first DOTS server
to provide accurate information. The DOTS client can then try to
establish a UDP or a TCP session with the alternate DOTS server
(Section 4.3). Note that state synchronization (e.g., signal session
configuration, aliases) is assumed to be in place between the
original and alternate DOTS servers; such synchronization means are
out of scope. If session configuration refresh is needed while
redirection is in place, the DOTS client follows the procedure
defined in Section 4.5.3. In 'idle' time and under some conditions
(e.g., infinite configuration lifetime, infinite redirection TTL, and
failure to refresh the configuration), the DOTS client follows the
procedure defined in Section 4.5.2 to negotiate the DOTS signal
channel session configuration with the alternate server. The DOTS
client MAY implement a method to construct IPv4-embedded IPv6
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addresses [RFC6052]; this is required to handle the scenario where an
IPv6-only DOTS client communicates with an IPv4-only alternate DOTS
server.
If the DOTS client has been redirected to a DOTS server with which it
has already communicated within the last five (5) minutes, it MUST
ignore the redirection and try to contact other DOTS servers listed
in the local configuration or discovered using dynamic means such as
DHCP or SRV procedures [RFC8973]. It is RECOMMENDED that DOTS
clients support the means to alert administrators about redirect
loops.
4.7. Heartbeat Mechanism
To provide an indication of signal health and to distinguish an
'idle' signal channel from a 'disconnected' or 'defunct' session, the
DOTS agent sends a heartbeat over the signal channel to maintain its
half of the channel (also, aligned with the "consents" recommendation
in Section 6 of [RFC8085]). The DOTS agent similarly expects a
heartbeat from its peer DOTS agent, and it may consider a session
terminated in the prolonged absence of a peer agent heartbeat.
Concretely, while the communication between the DOTS agents is
otherwise quiescent, the DOTS client will probe the DOTS server to
ensure it has maintained cryptographic state and vice versa. Such
probes can also keep the bindings of firewalls and/or stateful
translators alive. This probing reduces the frequency of
establishing a new handshake when a DOTS signal needs to be conveyed
to the DOTS server.
| Implementation Note: Given that CoAP roles can be multiplexed
| over the same session as discussed in [RFC7252] and are already
| supported by CoAP implementations, both the DOTS client and
| server can send DOTS heartbeat requests.
The DOTS heartbeat mechanism uses Non-confirmable PUT requests
(Figure 27) with an expected 2.04 (Changed) Response Code
(Figure 28). This procedure occurs between a DOTS agent and its
immediate peer DOTS agent. As such, this PUT request MUST NOT be
relayed by a DOTS gateway. The PUT request used for DOTS heartbeat
MUST NOT have a 'cuid', 'cdid', or 'mid' Uri-Path.
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Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "hb"
Content-Format: "application/dots+cbor"
{
"ietf-dots-signal-channel:heartbeat": {
"peer-hb-status": true
}
}
Figure 27: PUT to Check Peer DOTS Agent Is Responding
The mandatory 'peer-hb-status' attribute is set to 'true' (or
'false') to indicate that a DOTS agent is (or is not) receiving
heartbeat messages from its peer in the last (2 * 'heartbeat-
interval') period. Such information can be used by a peer DOTS agent
to detect or confirm connectivity issues and react accordingly. For
example, if a DOTS client receives a 2.04 response for its heartbeat
messages but no server-initiated heartbeat messages, the DOTS client
sets 'peer-hb-status' to 'false' in its next heartbeat message. Upon
receipt of this message, the DOTS server then will need to try
another strategy for sending the heartbeats (e.g., adjust the
heartbeat interval or send a server-initiated heartbeat immediately
after receiving a client-initiated heartbeat message).
Header: (Code=2.04)
Figure 28: Response to a DOTS Heartbeat Request (with an Empty Body)
DOTS servers MAY trigger their heartbeat requests immediately after
receiving heartbeat probes from peer DOTS clients. It is the
responsibility of DOTS clients to ensure that on-path translators/
firewalls are maintaining a binding so that the same external IP
address and/or port number is retained for the DOTS signal channel
session.
Under normal traffic conditions (i.e., no attack is ongoing), if a
DOTS agent does not receive any response from the peer DOTS agent for
'missing-hb-allowed' number of consecutive heartbeat messages, it
concludes that the DOTS signal channel session is disconnected. The
DOTS client MUST then try to reestablish the DOTS signal channel
session, preferably by resuming the (D)TLS session.
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| Note: If a new DOTS signal channel session cannot be
| established, the DOTS client SHOULD NOT retry to establish the
| DOTS signal channel session more frequently than every 300
| seconds (5 minutes) and MUST NOT retry more frequently than
| every 60 seconds (1 minute). It is recommended that DOTS
| clients support the means to alert administrators about the
| failure to establish a (D)TLS session.
In case of a massive DDoS attack that saturates the incoming link(s)
to the DOTS client, all traffic from the DOTS server to the DOTS
client will likely be dropped, although the DOTS server receives
heartbeat requests in addition to DOTS messages sent by the DOTS
client. In this scenario, DOTS clients MUST behave differently to
handle message transmission and DOTS signal channel session
liveliness during link saturation:
The DOTS client MUST NOT consider the DOTS signal channel session
terminated even after a maximum 'missing-hb-allowed' threshold is
reached. The DOTS client SHOULD keep on using the current DOTS
signal channel session to send heartbeat requests over it, so that
the DOTS server knows the DOTS client has not disconnected the
DOTS signal channel session.
After the maximum 'missing-hb-allowed' threshold is reached, the
DOTS client SHOULD try to establish a new DOTS signal channel
session. The DOTS client SHOULD send mitigation requests over the
current DOTS signal channel session and, in parallel, send the
mitigation requests over the new DOTS signal channel session.
This may be handled, for example, by resumption of the (D)TLS
session or using 0-RTT mode in DTLS 1.3 to piggyback the
mitigation request in the ClientHello message.
As soon as the link is no longer saturated, if traffic from the
DOTS server reaches the DOTS client over the current DOTS signal
channel session, the DOTS client can stop the new DOTS signal
channel session attempt or if a new DOTS signal channel session is
successful then disconnect the current DOTS signal channel
session.
If the DOTS server receives traffic from the peer DOTS client (e.g.,
peer DOTS client-initiated heartbeats) but the maximum 'missing-hb-
allowed' threshold is reached, the DOTS server MUST NOT consider the
DOTS signal channel session disconnected. The DOTS server MUST keep
on using the current DOTS signal channel session so that the DOTS
client can send mitigation requests over the current DOTS signal
channel session. In this case, the DOTS server can identify that the
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DOTS client is under attack and that the inbound link to the DOTS
client (domain) is saturated. Furthermore, if the DOTS server does
not receive a mitigation request from the DOTS client, it implies
that the DOTS client has not detected the attack or, if an attack
mitigation is in progress, it implies that the applied DDoS
mitigation actions are not yet effectively handling the DDoS attack
volume.
If the DOTS server does not receive any traffic from the peer DOTS
client during the time span required to exhaust the maximum 'missing-
hb-allowed' threshold, the DOTS server concludes the session is
disconnected. The DOTS server can then trigger preconfigured
mitigation requests for this DOTS client (if any).
In DOTS over TCP, the sender of a DOTS heartbeat message has to allow
up to 'heartbeat-interval' seconds when waiting for a heartbeat
reply. When a failure is detected by a DOTS client, it proceeds with
the session recovery, following the same approach as the one used for
unreliable transports.
5. DOTS Signal Channel YANG Modules
This document defines a YANG module [RFC7950] for DOTS mitigation
scope, DOTS signal channel session configuration data, DOTS
redirection signaling, and DOTS heartbeats.
This YANG module is not intended to be used via NETCONF/RESTCONF for
DOTS server management purposes; such a module is out of the scope of
this document. It serves only to provide abstract data structures.
This document uses the "structure" extension specified in [RFC8791].
A companion YANG module is defined to include a collection of types
defined by IANA: "iana-dots-signal-channel" (Section 5.2).
5.1. Tree Structure
This document defines the YANG module "ietf-dots-signal-channel",
which has the following tree structure. A DOTS signal message can be
a mitigation, a configuration, a redirect, or a heartbeat message.
This tree structure obsoletes the one described in Section 5.1 of
[RFC8782].
module: ietf-dots-signal-channel
structure dots-signal:
+-- (message-type)?
+--:(mitigation-scope)
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| +-- scope* []
| +-- target-prefix* inet:ip-prefix
| +-- target-port-range* [lower-port]
| | +-- lower-port inet:port-number
| | +-- upper-port? inet:port-number
| +-- target-protocol* uint8
| +-- target-fqdn* inet:domain-name
| +-- target-uri* inet:uri
| +-- alias-name* string
| +-- lifetime? union
| +-- trigger-mitigation? boolean
| +-- (direction)?
| +--:(server-to-client-only)
| | +-- mid? uint32
| | +-- mitigation-start? uint64
| | +-- status?
| | | iana-dots-signal:status
| | +-- conflict-information
| | | +-- conflict-status?
| | | | iana-dots-signal:conflict-status
| | | +-- conflict-cause?
| | | | iana-dots-signal:conflict-cause
| | | +-- retry-timer? uint32
| | | +-- conflict-scope
| | | +-- target-prefix* inet:ip-prefix
| | | +-- target-port-range* [lower-port]
| | | | +-- lower-port inet:port-number
| | | | +-- upper-port? inet:port-number
| | | +-- target-protocol* uint8
| | | +-- target-fqdn* inet:domain-name
| | | +-- target-uri* inet:uri
| | | +-- alias-name* string
| | | +-- acl-list* [acl-name]
| | | | +-- acl-name leafref
| | | | +-- acl-type? leafref
| | | +-- mid? uint32
| | +-- bytes-dropped?
| | | yang:zero-based-counter64
| | +-- bps-dropped? yang:gauge64
| | +-- pkts-dropped?
| | | yang:zero-based-counter64
| | +-- pps-dropped? yang:gauge64
| +--:(client-to-server-only)
| +-- attack-status?
| iana-dots-signal:attack-status
+--:(signal-config)
| +-- mitigating-config
| | +-- heartbeat-interval
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| | | +-- (direction)?
| | | | +--:(server-to-client-only)
| | | | +-- max-value? uint16
| | | | +-- min-value? uint16
| | | +-- current-value? uint16
| | +-- missing-hb-allowed
| | | +-- (direction)?
| | | | +--:(server-to-client-only)
| | | | +-- max-value? uint16
| | | | +-- min-value? uint16
| | | +-- current-value? uint16
| | +-- probing-rate
| | | +-- (direction)?
| | | | +--:(server-to-client-only)
| | | | +-- max-value? uint16
| | | | +-- min-value? uint16
| | | +-- current-value? uint16
| | +-- max-retransmit
| | | +-- (direction)?
| | | | +--:(server-to-client-only)
| | | | +-- max-value? uint16
| | | | +-- min-value? uint16
| | | +-- current-value? uint16
| | +-- ack-timeout
| | | +-- (direction)?
| | | | +--:(server-to-client-only)
| | | | +-- max-value-decimal? decimal64
| | | | +-- min-value-decimal? decimal64
| | | +-- current-value-decimal? decimal64
| | +-- ack-random-factor
| | +-- (direction)?
| | | +--:(server-to-client-only)
| | | +-- max-value-decimal? decimal64
| | | +-- min-value-decimal? decimal64
| | +-- current-value-decimal? decimal64
| +-- idle-config
| +-- heartbeat-interval
| | +-- (direction)?
| | | +--:(server-to-client-only)
| | | +-- max-value? uint16
| | | +-- min-value? uint16
| | +-- current-value? uint16
| +-- missing-hb-allowed
| | +-- (direction)?
| | | +--:(server-to-client-only)
| | | +-- max-value? uint16
| | | +-- min-value? uint16
| | +-- current-value? uint16
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| +-- probing-rate
| | +-- (direction)?
| | | +--:(server-to-client-only)
| | | +-- max-value? uint16
| | | +-- min-value? uint16
| | +-- current-value? uint16
| +-- max-retransmit
| | +-- (direction)?
| | | +--:(server-to-client-only)
| | | +-- max-value? uint16
| | | +-- min-value? uint16
| | +-- current-value? uint16
| +-- ack-timeout
| | +-- (direction)?
| | | +--:(server-to-client-only)
| | | +-- max-value-decimal? decimal64
| | | +-- min-value-decimal? decimal64
| | +-- current-value-decimal? decimal64
| +-- ack-random-factor
| +-- (direction)?
| | +--:(server-to-client-only)
| | +-- max-value-decimal? decimal64
| | +-- min-value-decimal? decimal64
| +-- current-value-decimal? decimal64
+--:(redirected-signal)
| +-- (direction)?
| +--:(server-to-client-only)
| +-- alt-server inet:domain-name
| +-- alt-server-record* inet:ip-address
+--:(heartbeat)
+-- peer-hb-status boolean
5.2. IANA DOTS Signal Channel YANG Module
This version obsoletes the version described in Section 5.2 of
[RFC8782].
<CODE BEGINS> file "iana-dots-signal-channel@2020-09-24.yang"
module iana-dots-signal-channel {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:iana-dots-signal-channel";
prefix iana-dots-signal;
organization
"IANA";
contact
"Internet Assigned Numbers Authority
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Postal: ICANN
12025 Waterfront Drive, Suite 300
Los Angeles, CA 90094-2536
United States of America
Tel: +1 310 301 5800
<mailto:iana@iana.org>";
description
"This module contains a collection of YANG data types defined
by IANA and used for DOTS signal channel protocol.
Copyright (c) 2021 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC 8782; see
the RFC itself for full legal notices.";
revision 2020-09-24 {
description
"Updated the prefix used for the module.";
reference
"RFC XXXX: Distributed Denial-of-Service Open Threat
Signaling (DOTS) Signal Channel Specification";
}
revision 2020-05-28 {
description
"Initial revision.";
reference
"RFC 8782: Distributed Denial-of-Service Open Threat
Signaling (DOTS) Signal Channel Specification";
}
typedef status {
type enumeration {
enum attack-mitigation-in-progress {
value 1;
description
"Attack mitigation setup is in progress (e.g., changing
the network path to reroute the inbound traffic
to DOTS mitigator).";
}
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enum attack-successfully-mitigated {
value 2;
description
"Attack is being successfully mitigated (e.g., traffic
is redirected to a DDoS mitigator and attack
traffic is dropped or blackholed).";
}
enum attack-stopped {
value 3;
description
"Attack has stopped and the DOTS client can
withdraw the mitigation request.";
}
enum attack-exceeded-capability {
value 4;
description
"Attack has exceeded the mitigation provider
capability.";
}
enum dots-client-withdrawn-mitigation {
value 5;
description
"DOTS client has withdrawn the mitigation
request and the mitigation is active but
terminating.";
}
enum attack-mitigation-terminated {
value 6;
description
"Attack mitigation is now terminated.";
}
enum attack-mitigation-withdrawn {
value 7;
description
"Attack mitigation is withdrawn.";
}
enum attack-mitigation-signal-loss {
value 8;
description
"Attack mitigation will be triggered
for the mitigation request only when
the DOTS signal channel session is lost.";
}
}
description
"Enumeration for status reported by the DOTS server.";
}
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typedef conflict-status {
type enumeration {
enum request-inactive-other-active {
value 1;
description
"DOTS Server has detected conflicting mitigation
requests from different DOTS clients.
This mitigation request is currently inactive
until the conflicts are resolved. Another
mitigation request is active.";
}
enum request-active {
value 2;
description
"DOTS Server has detected conflicting mitigation
requests from different DOTS clients.
This mitigation request is currently active.";
}
enum all-requests-inactive {
value 3;
description
"DOTS Server has detected conflicting mitigation
requests from different DOTS clients. All
conflicting mitigation requests are inactive.";
}
}
description
"Enumeration for conflict status.";
}
typedef conflict-cause {
type enumeration {
enum overlapping-targets {
value 1;
description
"Overlapping targets. conflict-scope provides
more details about the exact conflict.";
}
enum conflict-with-acceptlist {
value 2;
description
"Conflicts with an existing accept-list.
This code is returned when the DDoS mitigation
detects that some of the source addresses/prefixes
listed in the accept-list ACLs are actually
attacking the target.";
}
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enum cuid-collision {
value 3;
description
"Conflicts with the cuid used by another
DOTS client.";
}
}
description
"Enumeration for conflict causes.";
}
typedef attack-status {
type enumeration {
enum under-attack {
value 1;
description
"The DOTS client determines that it is still under
attack.";
}
enum attack-successfully-mitigated {
value 2;
description
"The DOTS client determines that the attack is
successfully mitigated.";
}
}
description
"Enumeration for attack status codes.";
}
}
<CODE ENDS>
5.3. IETF DOTS Signal Channel YANG Module
This module uses the common YANG types defined in [RFC6991] and types
defined in [RFC8783].
This version obsoletes the version described in Section 5.3 of
[RFC8782].
<CODE BEGINS> file "ietf-dots-signal-channel@2021-03-02.yang"
module ietf-dots-signal-channel {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-dots-signal-channel";
prefix dots-signal;
import ietf-inet-types {
prefix inet;
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reference
"Section 4 of RFC 6991";
}
import ietf-yang-types {
prefix yang;
reference
"Section 3 of RFC 6991";
}
import ietf-dots-data-channel {
prefix data-channel;
reference
"RFC 8783: Distributed Denial-of-Service Open Threat Signaling
(DOTS) Data Channel Specification";
}
import iana-dots-signal-channel {
prefix iana-dots-signal;
reference
"RFC XXXX: Distributed Denial-of-Service Open Threat Signaling
(DOTS) Signal Channel Specification";
}
import ietf-yang-structure-ext {
prefix sx;
reference
"RFC 8791: YANG Data Structure Extensions";
}
organization
"IETF DDoS Open Threat Signaling (DOTS) Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/dots/>
WG List: <mailto:dots@ietf.org>
Editor: Mohamed Boucadair
<mailto:mohamed.boucadair@orange.com>
Editor: Jon Shallow
<mailto:supjps-ietf@jpshallow.com>
Author: Konda, Tirumaleswar Reddy.K
<mailto:TirumaleswarReddy_Konda@McAfee.com>
Author: Prashanth Patil
<mailto:praspati@cisco.com>
Author: Andrew Mortensen
<mailto:amortensen@arbor.net>
Author: Nik Teague
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<mailto:nteague@ironmountain.co.uk>";
description
"This module contains YANG definition for the signaling
messages exchanged between a DOTS client and a DOTS server.
Copyright (c) 2021 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
revision 2021-03-02 {
description
"Updated revision to comply with RFC8791.
This version is not backward compatible with the version
published in RFC 8782.";
reference
"RFC XXXX: Distributed Denial-of-Service Open Threat
Signaling (DOTS) Signal Channel Specification";
}
revision 2020-05-28 {
description
"Initial revision.";
reference
"RFC 8782: Distributed Denial-of-Service Open Threat
Signaling (DOTS) Signal Channel Specification";
}
/*
* Groupings
*/
grouping mitigation-scope {
description
"Specifies the scope of the mitigation request.";
list scope {
description
"The scope of the request.";
uses data-channel:target;
leaf-list alias-name {
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type string;
description
"An alias name that points to a resource.";
}
leaf lifetime {
type union {
type uint32;
type int32 {
range "-1";
}
}
units "seconds";
default "3600";
description
"Indicates the lifetime of the mitigation request.
A lifetime of '0' in a mitigation request is an
invalid value.
A lifetime of negative one (-1) indicates indefinite
lifetime for the mitigation request.
Lifetime is mandatory in a mitigation request.
The DOTS server must always indicate the actual lifetime
in the response to an accepted mitigation request and the
remaining lifetime in status messages sent to the
DOTS client.";
}
leaf trigger-mitigation {
type boolean;
default "true";
description
"If set to 'false', DDoS mitigation will not be
triggered unless the DOTS signal channel
session is lost.";
}
choice direction {
description
"Indicates the communication direction in which the
data nodes can be included.";
case server-to-client-only {
description
"These data nodes appear only in a mitigation message
sent from the server to the client.";
leaf mid {
type uint32;
description
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"Mitigation request identifier.
This identifier must be unique for each mitigation
request bound to the DOTS client.";
}
leaf mitigation-start {
type uint64;
description
"Mitigation start time is represented in seconds
relative to 1970-01-01T00:00:00Z in UTC time.
This is a mandatory attribute when an attack mitigation
is active. It must not be returned for a
mitigation with 'status' code set to 8.";
}
leaf status {
type iana-dots-signal:status;
description
"Indicates the status of a mitigation request.
It must be included in responses only.
This is a mandatory attribute if a mitigation
request is accepted and processed by the server.";
}
container conflict-information {
description
"Indicates that a conflict is detected.";
leaf conflict-status {
type iana-dots-signal:conflict-status;
description
"Indicates the conflict status.";
}
leaf conflict-cause {
type iana-dots-signal:conflict-cause;
description
"Indicates the cause of the conflict.";
}
leaf retry-timer {
type uint32;
units "seconds";
description
"The DOTS client must not resend the
same request that has a conflict before the expiry of
this timer.";
}
container conflict-scope {
description
"Provides more information about the conflict scope.";
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uses data-channel:target {
when "/dots-signal/scope/conflict-information/"
+ "conflict-cause = 'overlapping-targets'";
}
leaf-list alias-name {
when "../../conflict-cause = 'overlapping-targets'";
type string;
description
"Conflicting alias-name.";
}
list acl-list {
when "../../conflict-cause ="
+ " 'conflict-with-acceptlist'";
key "acl-name";
description
"List of conflicting ACLs as defined in the DOTS data
channel. These ACLs are uniquely defined by
cuid and acl-name.";
leaf acl-name {
type leafref {
path "/data-channel:dots-data"
+ "/data-channel:dots-client/data-channel:acls"
+ "/data-channel:acl/data-channel:name";
}
description
"Reference to the conflicting ACL name bound to
a DOTS client.";
}
leaf acl-type {
type leafref {
path "/data-channel:dots-data"
+ "/data-channel:dots-client/data-channel:acls"
+ "/data-channel:acl/data-channel:type";
}
description
"Reference to the conflicting ACL type bound to
a DOTS client.";
}
}
leaf mid {
when "../../conflict-cause = 'overlapping-targets'";
type uint32;
description
"Reference to the conflicting 'mid' bound to
the same DOTS client.";
}
}
}
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leaf bytes-dropped {
type yang:zero-based-counter64;
units "bytes";
description
"The total dropped byte count for the mitigation
request since the attack mitigation was triggered.
The count wraps around when it reaches the maximum value
of counter64 for dropped bytes.";
}
leaf bps-dropped {
type yang:gauge64;
units "bytes per second";
description
"The average number of dropped bytes per second for
the mitigation request since the attack
mitigation was triggered. This should be over
five-minute intervals (that is, measuring bytes
into five-minute buckets and then averaging these
buckets over the time since the mitigation was
triggered).";
}
leaf pkts-dropped {
type yang:zero-based-counter64;
description
"The total number of dropped packet count for the
mitigation request since the attack mitigation was
triggered. The count wraps around when it reaches
the maximum value of counter64 for dropped packets.";
}
leaf pps-dropped {
type yang:gauge64;
units "packets per second";
description
"The average number of dropped packets per second
for the mitigation request since the attack
mitigation was triggered. This should be over
five-minute intervals (that is, measuring packets
into five-minute buckets and then averaging these
buckets over the time since the mitigation was
triggered).";
}
}
case client-to-server-only {
description
"These data nodes appear only in a mitigation message
sent from the client to the server.";
leaf attack-status {
type iana-dots-signal:attack-status;
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description
"Indicates the status of an attack as seen by the
DOTS client.
This is a mandatory attribute when a client
performs an efficacy update.";
}
}
}
}
}
grouping config-parameters {
description
"Subset of DOTS signal channel session configuration.";
container heartbeat-interval {
description
"DOTS agents regularly send heartbeats to each other
after mutual authentication is successfully
completed in order to keep the DOTS signal channel
open.";
choice direction {
description
"Indicates the communication direction in which the
data nodes can be included.";
case server-to-client-only {
description
"These data nodes appear only in a mitigation message
sent from the server to the client.";
leaf max-value {
type uint16;
units "seconds";
description
"Maximum acceptable heartbeat-interval value.";
}
leaf min-value {
type uint16;
units "seconds";
description
"Minimum acceptable heartbeat-interval value.";
}
}
}
leaf current-value {
type uint16;
units "seconds";
default "30";
description
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"Current heartbeat-interval value.
'0' means that heartbeat mechanism is deactivated.";
}
}
container missing-hb-allowed {
description
"Maximum number of missing heartbeats allowed.";
choice direction {
description
"Indicates the communication direction in which the
data nodes can be included.";
case server-to-client-only {
description
"These data nodes appear only in a mitigation message
sent from the server to the client.";
leaf max-value {
type uint16;
description
"Maximum acceptable missing-hb-allowed value.";
}
leaf min-value {
type uint16;
description
"Minimum acceptable missing-hb-allowed value.";
}
}
}
leaf current-value {
type uint16;
default "15";
description
"Current missing-hb-allowed value.";
}
}
container probing-rate {
description
"The limit for sending Non-confirmable messages with
no response.";
choice direction {
description
"Indicates the communication direction in which the
data nodes can be included.";
case server-to-client-only {
description
"These data nodes appear only in a mitigation message
sent from the server to the client.";
leaf max-value {
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type uint16;
units "byte/second";
description
"Maximum acceptable probing-rate value.";
}
leaf min-value {
type uint16;
units "byte/second";
description
"Minimum acceptable probing-rate value.";
}
}
}
leaf current-value {
type uint16;
units "byte/second";
default "5";
description
"Current probing-rate value.";
}
}
container max-retransmit {
description
"Maximum number of retransmissions of a Confirmable
message.";
choice direction {
description
"Indicates the communication direction in which the
data nodes can be included.";
case server-to-client-only {
description
"These data nodes appear only in a mitigation message
sent from the server to the client.";
leaf max-value {
type uint16;
description
"Maximum acceptable max-retransmit value.";
}
leaf min-value {
type uint16;
description
"Minimum acceptable max-retransmit value.";
}
}
}
leaf current-value {
type uint16;
default "3";
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description
"Current max-retransmit value.";
}
}
container ack-timeout {
description
"Initial retransmission timeout value.";
choice direction {
description
"Indicates the communication direction in which the
data nodes can be included.";
case server-to-client-only {
description
"These data nodes appear only in a mitigation message
sent from the server to the client.";
leaf max-value-decimal {
type decimal64 {
fraction-digits 2;
}
units "seconds";
description
"Maximum ack-timeout value.";
}
leaf min-value-decimal {
type decimal64 {
fraction-digits 2;
}
units "seconds";
description
"Minimum ack-timeout value.";
}
}
}
leaf current-value-decimal {
type decimal64 {
fraction-digits 2;
}
units "seconds";
default "2";
description
"Current ack-timeout value.";
}
}
container ack-random-factor {
description
"Random factor used to influence the timing of
retransmissions.";
choice direction {
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description
"Indicates the communication direction in which the
data nodes can be included.";
case server-to-client-only {
description
"These data nodes appear only in a mitigation message
sent from the server to the client.";
leaf max-value-decimal {
type decimal64 {
fraction-digits 2;
}
description
"Maximum acceptable ack-random-factor value.";
}
leaf min-value-decimal {
type decimal64 {
fraction-digits 2;
}
description
"Minimum acceptable ack-random-factor value.";
}
}
}
leaf current-value-decimal {
type decimal64 {
fraction-digits 2;
}
default "1.5";
description
"Current ack-random-factor value.";
}
}
}
grouping signal-config {
description
"DOTS signal channel session configuration.";
container mitigating-config {
description
"Configuration parameters to use when a mitigation
is active.";
uses config-parameters;
}
container idle-config {
description
"Configuration parameters to use when no mitigation
is active.";
uses config-parameters;
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}
}
grouping redirected-signal {
description
"Grouping for the redirected signaling.";
choice direction {
description
"Indicates the communication direction in which the
data nodes can be included.";
case server-to-client-only {
description
"These data nodes appear only in a mitigation message
sent from the server to the client.";
leaf alt-server {
type inet:domain-name;
mandatory true;
description
"FQDN of an alternate server.";
}
leaf-list alt-server-record {
type inet:ip-address;
description
"List of records for the alternate server.";
}
}
}
}
/*
* DOTS Signal Channel Structure
*/
sx:structure dots-signal {
description
"Main structure for DOTS signal message.
A DOTS signal message can be a mitigation, a configuration,
a redirected, or a heartbeat signal message.";
choice message-type {
description
"Can be a mitigation, a configuration, a redirect, or
a heartbeat message.";
case mitigation-scope {
description
"Mitigation scope of a mitigation message.";
uses mitigation-scope;
}
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case signal-config {
description
"Configuration message.";
uses signal-config;
}
case redirected-signal {
description
"Redirected signaling.";
uses redirected-signal;
}
case heartbeat {
description
"DOTS heartbeats.";
leaf peer-hb-status {
type boolean;
mandatory true;
description
"Indicates whether a DOTS agent receives heartbeats
from its peer. The value is set to 'true' if the
DOTS agent is receiving heartbeat messages
from its peer.";
}
}
}
}
}
<CODE ENDS>
6. YANG/JSON Mapping Parameters to CBOR
All parameters in the payload of the DOTS signal channel MUST be
mapped to CBOR types as shown in Table 5 and are assigned an integer
key to save space.
Note: Implementers must check that the mapping output provided by
their YANG-to-CBOR encoding schemes is aligned with the content of
Table 5. For example, some CBOR and JSON types for enumerations
and the 64-bit quantities can differ depending on the encoder
used.
The CBOR key values are divided into two types: comprehension-
required and comprehension-optional. DOTS agents can safely ignore
comprehension-optional values they don't understand, but they cannot
successfully process a request if it contains comprehension-required
values that are not understood. The 4.00 response SHOULD include a
diagnostic payload describing the unknown comprehension-required CBOR
key values. The initial set of CBOR key values defined in this
specification are of type comprehension-required.
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+---------------------+--------------+------+-------------+--------+
| Parameter Name | YANG Type | CBOR | CBOR Major | JSON |
| | | Key | Type & | Type |
| | | | Information | |
+=====================+==============+======+=============+========+
| ietf-dots-signal- | container | 1 | 5 map | Object |
| channel:mitigation- | | | | |
| scope | | | | |
+---------------------+--------------+------+-------------+--------+
| scope | list | 2 | 4 array | Array |
+---------------------+--------------+------+-------------+--------+
| cdid | string | 3 | 3 text | String |
| | | | string | |
+---------------------+--------------+------+-------------+--------+
| cuid | string | 4 | 3 text | String |
| | | | string | |
+---------------------+--------------+------+-------------+--------+
| mid | uint32 | 5 | 0 unsigned | Number |
+---------------------+--------------+------+-------------+--------+
| target-prefix | leaf-list | 6 | 4 array | Array |
| +--------------+------+-------------+--------+
| | inet:ip- | | 3 text | String |
| | prefix | | string | |
+---------------------+--------------+------+-------------+--------+
| target-port-range | list | 7 | 4 array | Array |
+---------------------+--------------+------+-------------+--------+
| lower-port | inet:port- | 8 | 0 unsigned | Number |
| | number | | | |
+---------------------+--------------+------+-------------+--------+
| upper-port | inet:port- | 9 | 0 unsigned | Number |
| | number | | | |
+---------------------+--------------+------+-------------+--------+
| target-protocol | leaf-list | 10 | 4 array | Array |
| +--------------+------+-------------+--------+
| | uint8 | | 0 unsigned | Number |
+---------------------+--------------+------+-------------+--------+
| target-fqdn | leaf-list | 11 | 4 array | Array |
| +--------------+------+-------------+--------+
| | inet:domain- | | 3 text | String |
| | name | | string | |
+---------------------+--------------+------+-------------+--------+
| target-uri | leaf-list | 12 | 4 array | Array |
| +--------------+------+-------------+--------+
| | inet:uri | | 3 text | String |
| | | | string | |
+---------------------+--------------+------+-------------+--------+
| alias-name | leaf-list | 13 | 4 array | Array |
| +--------------+------+-------------+--------+
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| | string | | 3 text | String |
| | | | string | |
+---------------------+--------------+------+-------------+--------+
| lifetime | union | 14 | 0 unsigned | Number |
| | | +-------------+--------+
| | | | 1 negative | Number |
+---------------------+--------------+------+-------------+--------+
| mitigation-start | uint64 | 15 | 0 unsigned | String |
+---------------------+--------------+------+-------------+--------+
| status | enumeration | 16 | 0 unsigned | String |
+---------------------+--------------+------+-------------+--------+
| conflict- | container | 17 | 5 map | Object |
| information | | | | |
+---------------------+--------------+------+-------------+--------+
| conflict-status | enumeration | 18 | 0 unsigned | String |
+---------------------+--------------+------+-------------+--------+
| conflict-cause | enumeration | 19 | 0 unsigned | String |
+---------------------+--------------+------+-------------+--------+
| retry-timer | uint32 | 20 | 0 unsigned | String |
+---------------------+--------------+------+-------------+--------+
| conflict-scope | container | 21 | 5 map | Object |
+---------------------+--------------+------+-------------+--------+
| acl-list | list | 22 | 4 array | Array |
+---------------------+--------------+------+-------------+--------+
| acl-name | leafref | 23 | 3 text | String |
| | | | string | |
+---------------------+--------------+------+-------------+--------+
| acl-type | leafref | 24 | 3 text | String |
| | | | string | |
+---------------------+--------------+------+-------------+--------+
| bytes-dropped | yang:zero- | 25 | 0 unsigned | String |
| | based- | | | |
| | counter64 | | | |
+---------------------+--------------+------+-------------+--------+
| bps-dropped | yang:gauge64 | 26 | 0 unsigned | String |
+---------------------+--------------+------+-------------+--------+
| pkts-dropped | yang:zero- | 27 | 0 unsigned | String |
| | based- | | | |
| | counter64 | | | |
+---------------------+--------------+------+-------------+--------+
| pps-dropped | yang:gauge64 | 28 | 0 unsigned | String |
+---------------------+--------------+------+-------------+--------+
| attack-status | enumeration | 29 | 0 unsigned | String |
+---------------------+--------------+------+-------------+--------+
| ietf-dots-signal- | container | 30 | 5 map | Object |
| channel:signal- | | | | |
| config | | | | |
+---------------------+--------------+------+-------------+--------+
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| sid | uint32 | 31 | 0 unsigned | Number |
+---------------------+--------------+------+-------------+--------+
| mitigating-config | container | 32 | 5 map | Object |
+---------------------+--------------+------+-------------+--------+
| heartbeat-interval | container | 33 | 5 map | Object |
+---------------------+--------------+------+-------------+--------+
| max-value | uint16 | 34 | 0 unsigned | Number |
+---------------------+--------------+------+-------------+--------+
| min-value | uint16 | 35 | 0 unsigned | Number |
+---------------------+--------------+------+-------------+--------+
| current-value | uint16 | 36 | 0 unsigned | Number |
+---------------------+--------------+------+-------------+--------+
| missing-hb-allowed | container | 37 | 5 map | Object |
+---------------------+--------------+------+-------------+--------+
| max-retransmit | container | 38 | 5 map | Object |
+---------------------+--------------+------+-------------+--------+
| ack-timeout | container | 39 | 5 map | Object |
+---------------------+--------------+------+-------------+--------+
| ack-random-factor | container | 40 | 5 map | Object |
+---------------------+--------------+------+-------------+--------+
| max-value-decimal | decimal64 | 41 | 6 tag 4 | String |
| | | | [-2, | |
| | | | integer] | |
+---------------------+--------------+------+-------------+--------+
| min-value-decimal | decimal64 | 42 | 6 tag 4 | String |
| | | | [-2, | |
| | | | integer] | |
+---------------------+--------------+------+-------------+--------+
| current-value- | decimal64 | 43 | 6 tag 4 | String |
| decimal | | | [-2, | |
| | | | integer] | |
+---------------------+--------------+------+-------------+--------+
| idle-config | container | 44 | 5 map | Object |
+---------------------+--------------+------+-------------+--------+
| trigger-mitigation | boolean | 45 | 7 bits 20 | False |
| | | +-------------+--------+
| | | | 7 bits 21 | True |
+---------------------+--------------+------+-------------+--------+
| ietf-dots-signal- | container | 46 | 5 map | Object |
| channel:redirected- | | | | |
| signal | | | | |
+---------------------+--------------+------+-------------+--------+
| alt-server | inet:domain- | 47 | 3 text | String |
| | name | | string | |
+---------------------+--------------+------+-------------+--------+
| alt-server-record | leaf-list | 48 | 4 array | Array |
| +--------------+------+-------------+--------+
| | inet:ip- | | 3 text | String |
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| | address | | string | |
+---------------------+--------------+------+-------------+--------+
| ietf-dots-signal- | container | 49 | 5 map | Object |
| channel:heartbeat | | | | |
+---------------------+--------------+------+-------------+--------+
| probing-rate | container | 50 | 5 map | Object |
+---------------------+--------------+------+-------------+--------+
| peer-hb-status | boolean | 51 | 7 bits 20 | False |
| | | +-------------+--------+
| | | | 7 bits 21 | True |
+---------------------+--------------+------+-------------+--------+
Table 5: CBOR Key Values Used in DOTS Signal Channel Messages &
Their Mappings to JSON and YANG
7. (D)TLS Protocol Profile and Performance Considerations
7.1. (D)TLS Protocol Profile
This section defines the (D)TLS protocol profile of DOTS signal
channel over (D)TLS and DOTS data channel over TLS.
There are known attacks on (D)TLS, such as man-in-the-middle and
protocol downgrade attacks. These are general attacks on (D)TLS and,
as such, they are not specific to DOTS over (D)TLS; refer to the
(D)TLS RFCs for discussion of these security issues. DOTS agents
MUST adhere to the (D)TLS implementation recommendations and security
considerations of [RFC7525] except with respect to (D)TLS version.
Because DOTS signal channel encryption relying upon (D)TLS is
virtually a greenfield deployment, DOTS agents MUST implement only
(D)TLS 1.2 or later.
When a DOTS client is configured with a domain name of the DOTS
server, and it connects to its configured DOTS server, the server may
present it with a PKIX certificate. In order to ensure proper
authentication, a DOTS client MUST verify the entire certification
path per [RFC5280]. Additionally, the DOTS client MUST use [RFC6125]
validation techniques to compare the domain name with the certificate
provided. Certification authorities that issue DOTS server
certificates SHOULD support the DNS-ID and SRV-ID identifier types.
DOTS servers SHOULD prefer the use of DNS-ID and SRV-ID over CN-ID
identifier types in certificate requests (as described in Section 2.3
of [RFC6125]), and the wildcard character '*' SHOULD NOT be included
in the presented identifier. DOTS doesn't use URI-IDs for server
identity verification.
A key challenge to deploying DOTS is the provisioning of DOTS
clients, including the distribution of keying material to DOTS
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clients to enable the required mutual authentication of DOTS agents.
Enrollment over Secure Transport (EST) [RFC7030] defines a method of
certificate enrollment by which domains operating DOTS servers may
provide DOTS clients with all the necessary cryptographic keying
material, including a private key and a certificate, to authenticate
themselves. One deployment option is to have DOTS clients behave as
EST clients for certificate enrollment from an EST server provisioned
by the mitigation provider. This document does not specify which EST
or other mechanism the DOTS client uses to achieve initial
enrollment.
The Server Name Indication (SNI) extension [RFC6066] defines a
mechanism for a client to tell a (D)TLS server the name of the server
it wants to contact. This is a useful extension for hosting
environments where multiple virtual servers are reachable over a
single IP address. The DOTS client may or may not know if it is
interacting with a DOTS server in a virtual server hosting
environment, so the DOTS client SHOULD include the DOTS server FQDN
in the SNI extension.
Implementations compliant with this profile MUST implement all of the
following items:
o DTLS record replay detection (Section 3.3 of [RFC6347]) or an
equivalent mechanism to protect against replay attacks.
o DTLS session resumption without server-side state to resume
session and convey the DOTS signal.
o At least one of raw public keys [RFC7250] or PSK handshake
[RFC4279] with (EC)DHE key exchange. This reduces the size of the
ServerHello. Also, this can be used by DOTS agents that cannot
obtain certificates.
Implementations compliant with this profile SHOULD implement all of
the following items to reduce the delay required to deliver a DOTS
signal channel message:
o TLS False Start [RFC7918], which reduces round-trips by allowing
the TLS client's second flight of messages (ChangeCipherSpec) to
also contain the DOTS signal. TLS False Start is formally defined
for use with TLS, but the same technique is applicable to DTLS as
well.
o Cached Information Extension [RFC7924] which avoids transmitting
the server's certificate and certificate chain if the client has
cached that information from a previous TLS handshake.
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Compared to UDP, DOTS signal channel over TCP requires an additional
round-trip time (RTT) of latency to establish a TCP connection. DOTS
implementations are encouraged to implement TCP Fast Open [RFC7413]
to eliminate that RTT.
7.2. (D)TLS 1.3 Considerations
TLS 1.3 provides useful latency improvements for connection
establishment over TLS 1.2. The DTLS 1.3 protocol
[I-D.ietf-tls-dtls13] is based upon the TLS 1.3 protocol and provides
equivalent security guarantees. (D)TLS 1.3 provides two basic
handshake modes the DOTS signal channel can take advantage of:
o A full handshake mode in which a DOTS client can send a DOTS
mitigation request message after one round trip and the DOTS
server immediately responds with a DOTS mitigation response. This
assumes no packet loss is experienced.
o 0-RTT mode in which the DOTS client can authenticate itself and
send DOTS mitigation request messages in the first message, thus
reducing handshake latency. 0-RTT only works if the DOTS client
has previously communicated with that DOTS server, which is very
likely with the DOTS signal channel.
The DOTS client has to establish a (D)TLS session with the DOTS
server during 'idle' time and share a PSK.
During a DDoS attack, the DOTS client can use the (D)TLS session to
convey the DOTS mitigation request message and, if there is no
response from the server after multiple retries, the DOTS client can
resume the (D)TLS session in 0-RTT mode using PSK.
DOTS servers that support (D)TLS 1.3 MAY allow DOTS clients to send
early data (0-RTT). DOTS clients MUST NOT send "CoAP Ping" as early
data; such messages MUST be rejected by DOTS servers. Section 8 of
[RFC8446] discusses some mechanisms to implement in order to limit
the impact of replay attacks on 0-RTT data. If the DOTS server
accepts 0-RTT, it MUST implement one of these mechanisms to prevent
replay at the TLS layer. A DOTS server can reject 0-RTT by sending a
TLS HelloRetryRequest.
The DOTS signal channel messages sent as early data by the DOTS
client are idempotent requests. As a reminder, the Message ID
(Section 3 of [RFC7252]) is changed each time a new CoAP request is
sent, and the Token (Section 5.3.1 of [RFC7252]) is randomized in
each CoAP request. The DOTS server(s) MUST use the Message ID and
the Token in the DOTS signal channel message to detect replay of
early data at the application layer and accept 0-RTT data at most
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once from the same DOTS client. This anti-replay defense requires
sharing the Message ID and the Token in the 0-RTT data between DOTS
servers in the DOTS server domain. DOTS servers do not rely on
transport coordinates to identify DOTS peers. As specified in
Section 4.4.1, DOTS servers couple the DOTS signal channel sessions
using the DOTS client identity and optionally the 'cdid' parameter
value. Furthermore, the 'mid' value is monotonically increased by
the DOTS client for each mitigation request, thus attackers that
replay mitigation requests with lower numeric 'mid' values and
overlapping scopes with mitigation requests having higher numeric
'mid' values will be rejected systematically by the DOTS server.
Likewise, the 'sid' value is monotonically increased by the DOTS
client for each configuration request (Section 4.5.2); attackers
replaying configuration requests with lower numeric 'sid' values will
be rejected by the DOTS server if it maintains a higher numeric 'sid'
value for this DOTS client.
Owing to the aforementioned protections, all DOTS signal channel
requests are safe to transmit in TLS 1.3 as early data. Refer to
[I-D.boucadair-dots-earlydata] for more details.
A simplified TLS 1.3 handshake with 0-RTT DOTS mitigation request
message exchange is shown in Figure 29.
DOTS Client DOTS Server
ClientHello
(0-RTT DOTS signal message)
-------->
ServerHello
{EncryptedExtensions}
{Finished}
<-------- [DOTS signal message]
(end_of_early_data)
{Finished} -------->
[DOTS signal message] <-------> [DOTS signal message]
Note that:
() Indicates messages protected 0-RTT keys
{} Indicates messages protected using handshake keys
[] Indicates messages protected using 1-RTT keys
Figure 29: A Simplified TLS 1.3 Handshake with 0-RTT
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7.3. DTLS MTU and Fragmentation
To avoid DOTS signal message fragmentation and the subsequent
decreased probability of message delivery, the DLTS records need to
fit within a single datagram [RFC6347]. DTLS handles fragmentation
and reassembly only for handshake messages and not for the
application data (Section 4.1.1 of [RFC6347]). If the path MTU
(PMTU) cannot be discovered, DOTS agents MUST assume a PMTU of 1280
bytes, as IPv6 requires that every link in the Internet have an MTU
of 1280 octets or greater as specified in [RFC8200]. If IPv4 support
on legacy or otherwise unusual networks is a consideration and the
PMTU is unknown, DOTS implementations MAY assume a PMTU of 576 bytes
for IPv4 datagrams (see Section 3.3.3 of [RFC1122]).
The DOTS client must consider the amount of record expansion expected
by the DTLS processing when calculating the size of the CoAP message
that fits within the PMTU. PMTU MUST be greater than or equal to
[CoAP message size + DTLS 1.2 overhead of 13 octets + authentication
overhead of the negotiated DTLS cipher suite + block padding]
(Section 4.1.1.1 of [RFC6347]). If the total request size exceeds
the PMTU, then the DOTS client MUST split the DOTS signal into
separate messages; for example, the list of addresses in the 'target-
prefix' parameter could be split into multiple lists and each list
conveyed in a new PUT request.
| Implementation Note: DOTS choice of message size parameters
| works well with IPv6 and with most of today's IPv4 paths.
| However, with IPv4, it is harder to safely make sure that there
| is no IP fragmentation. If the IPv4 PMTU is unknown,
| implementations may want to limit themselves to more
| conservative IPv4 datagram sizes such as 576 bytes, per
| [RFC0791].
8. Mutual Authentication of DOTS Agents & Authorization of DOTS Clients
(D)TLS based upon client certificates can be used for mutual
authentication between DOTS agents. If, for example, a DOTS gateway
is involved, DOTS clients and DOTS gateways must perform mutual
authentication; only authorized DOTS clients are allowed to send DOTS
signals to a DOTS gateway. The DOTS gateway and the DOTS server must
perform mutual authentication; a DOTS server only allows DOTS signal
channel messages from an authorized DOTS gateway, thereby creating a
two-link chain of transitive authentication between the DOTS client
and the DOTS server.
The DOTS server should support certificate-based client
authentication. The DOTS client should respond to the DOTS server's
TLS CertificateRequest message with the PKIX certificate held by the
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DOTS client. DOTS client certificate validation must be performed
per [RFC5280], and the DOTS client certificate must conform to the
[RFC5280] certificate profile. If a DOTS client does not support TLS
client certificate authentication, it must support client
authentication based on pre-shared key or raw public key.
+---------------------------------------------+
| example.com domain +---------+ |
| | AAA | |
| +---------------+ | Server | |
| | Application | +------+--+ |
| | server +<---------------+ ^ |
| | (DOTS client) | | | |
| +---------------+ | | |
| V V | example.net domain
| +-----+----+--+ | +---------------+
| +--------------+ | | | | |
| | Guest +<----x---->+ DOTS +<----->+ DOTS |
| | (DOTS client)| | gateway | | | server |
| +--------------+ | | | | |
| +----+--------+ | +---------------+
| ^ |
| | |
| +----------------+ | |
| | DDoS detector | | |
| | (DOTS client) +<-------------+ |
| +----------------+ |
+---------------------------------------------+
Figure 30: Example of Authentication and Authorization of DOTS Agents
In the example depicted in Figure 30, the DOTS gateway and DOTS
clients within the 'example.com' domain proceed with mutual
authentication. After the DOTS gateway validates the identity of a
DOTS client, it communicates with the AAA server in the 'example.com'
domain to determine if the DOTS client is authorized to request DDoS
mitigation. If the DOTS client is not authorized, a 4.01
(Unauthorized) is returned in the response to the DOTS client. In
this example, the DOTS gateway only allows the application server and
DDoS attack detector to request DDoS mitigation, but does not permit
the user of type 'guest' to request DDoS mitigation.
Also, DOTS gateways and servers located in different domains must
perform mutual authentication (e.g., using certificates). A DOTS
server will only allow a DOTS gateway with a certificate for a
particular domain to request mitigation for that domain. In
reference to Figure 30, the DOTS server only allows the DOTS gateway
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to request mitigation for the 'example.com' domain and not for other
domains.
9. Error Handling
This section is a summary of the Error Code responses that can be
returned by a DOTS server. These error responses must contain a CoAP
4.xx or 5.xx Response Code.
In general, there may be an additional plain text diagnostic payload
(Section 5.5.2 of [RFC7252]) to help troubleshooting in the body of
the response unless detailed otherwise.
Errors returned by a DOTS server can be broken into two categories,
those associated with CoAP itself and those generated during the
validation of the provided data by the DOTS server.
The following list of common CoAP errors that are implemented by DOTS
servers. This list is not exhaustive; other errors defined by CoAP
and associated RFCs may be applicable.
4.00 (Bad Request) is returned by the DOTS server when the DOTS
client has sent a request that violates the DOTS protocol
(Section 4).
4.01 (Unauthorized) is returned by the DOTS server when the DOTS
client is not authorized to access the DOTS server (Section 4).
4.02 (Bad Option) is returned by the DOTS server when one or more
CoAP options are unknown or malformed by the CoAP layer [RFC7252].
4.04 (Not Found) is returned by the DOTS server when the DOTS client
is requesting a 'mid' or 'sid' that is not valid (Section 4).
4.05 (Method Not Allowed) is returned by the DOTS server when the
DOTS client is requesting a resource by a method (e.g., GET) that
is not supported by the DOTS server [RFC7252].
4.08 (Request Entity Incomplete) is returned by the DOTS server if
one or multiple blocks of a block transfer request is missing
[RFC7959].
4.09 (Conflict) is returned by the DOTS server if the DOTS server
detects that a request conflicts with a previous request. The
response body is formatted using "application/dots+cbor", and
contains the "conflict-clause" (Section 4.4).
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4.13 (Request Entity Too Large) may be returned by the DOTS server
during a block transfer request [RFC7959].
4.15 (Unsupported Content-Format) is returned by the DOTS server
when the Content-Format is used but the request is not formatted
as "application/dots+cbor" (Section 4).
4.22 (Unprocessable Entity) is returned by the DOTS server when one
or more session configuration parameters are not valid
(Section 4.5).
5.03 (Service Unavailable) is returned by the DOTS server if the
DOTS server is unable to handle the request (Section 4). An
example is the DOTS server needs to redirect the DOTS client to
use an alternate DOTS server (Section 4.6). The response body is
formatted using "application/dots+cbor", and contains how to
handle the 5.03 Response Code.
5.08 (Hop Limit Reached) is returned by the DOTS server if there is
a data path loop through upstream DOTS gateways. The response
body is formatted using plain text and contains a list of servers
that are in the data path loop [RFC8768].
10. IANA Considerations
10.1. DOTS Signal Channel UDP and TCP Port Number
IANA has assigned the port number 4646 (the ASCII decimal value for
".." (DOTS)) to the DOTS signal channel protocol for both UDP and TCP
from the "Service Name and Transport Protocol Port Number Registry"
available at <https://www.iana.org/assignments/service-names-port-
numbers/>.
IANA is requested to update these entries with the RFC number to be
assigned to this document:
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Service Name: dots-signal
Port Number: 4646
Transport Protocol: TCP
Description: Distributed Denial-of-Service Open Threat Signaling
(DOTS) Signal Channel
Assignee: IESG
Contact: IETF Chair
Registration Date: 2020-01-16
Reference: [RFCXXXX]
Service Name: dots-signal
Port Number: 4646
Transport Protocol: UDP
Description: Distributed Denial-of-Service Open Threat Signaling
(DOTS) Signal Channel
Assignee: IESG
Contact: IETF Chair
Registration Date: 2020-01-16
Reference: [RFCXXXX]
10.2. Well-Known 'dots' URI
IANA is requested to update the 'dots' well-known URI (Table 6) entry
in the Well- Known URIs registry [URI] as follows:
+------------+------------+-----------+-----------+-------------+
| URI Suffix | Change | Reference | Status | Related |
| | Controller | | | information |
+============+============+===========+===========+=============+
| dots | IETF | [RFCXXXX] | permanent | None |
+------------+------------+-----------+-----------+-------------+
Table 6: 'dots' Well-Known URI
10.3. Media Type Registration
IANA is requested to update the "application/dots+cbor" media type in
the "Media Types" registry [IANA-MediaTypes] in the manner described
in [RFC6838], which can be used to indicate that the content is a
DOTS signal channel object:
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Type name: application
Subtype name: dots+cbor
Required parameters: N/A
Optional parameters: N/A
Encoding considerations: binary
Security considerations: See the Security Considerations section of
[RFCXXXX].
Interoperability considerations: N/A
Published specification: [RFCXXXX]
Applications that use this media type: DOTS agents sending DOTS
messages over CoAP over (D)TLS.
Fragment identifier considerations: N/A
Additional information:
Deprecated alias names for this type: N/A
Magic number(s): N/A
File extension(s): N/A
Macintosh file type code(s): N/A
Person & email address to contact for further information: IESG,
iesg@ietf.org
Intended usage: COMMON
Restrictions on usage: none
Author: See Authors' Addresses section.
Change controller: IESG
Provisional registration? No
10.4. CoAP Content-Formats Registration
IANA is requested to update the CoAP Content-Format ID for the
"application/ dots+cbor" media type in the "CoAP Content-Formats"
registry [IANA-CoAP-Content-Formats]:
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o Media Type: application/dots+cbor
o Encoding: -
o Id: 271
o Reference: [RFCXXXX]
10.5. CBOR Tag Registration
This section defines the DOTS CBOR tag as another means for
applications to declare that a CBOR data structure is a DOTS signal
channel object. Its use is optional and is intended for use in cases
in which this information would not otherwise be known. The DOTS
CBOR tag is not required for DOTS signal channel protocol version
specified in this document. If present, the DOTS tag MUST prefix a
DOTS signal channel object.
IANA is requested to update the DOTS signal channel CBOR tag in the
"CBOR Tags" registry [IANA-CBOR-Tags]:
* Tag: 271
* Data Item: DDoS Open Threat Signaling (DOTS) signal channel object
* Semantics: DDoS Open Threat Signaling (DOTS) signal channel
object, as defined in [RFCXXXX]
* Reference: [RFCXXXX]
10.6. DOTS Signal Channel Protocol Registry
The following sections update the "Distributed Denial-of- Service
Open Threat Signaling (DOTS) Signal Channel" subregistries
[REG-DOTS].
10.6.1. DOTS Signal Channel CBOR Key Values Subregistry
The structure of this subregistry is provided in Section 10.6.1.1.
10.6.1.1. Registration Template
This specification requests IANA to update the allocation policy of
"DOTS Signal Channel CBOR Key Values" registry as follows:
Parameter name:
Parameter name as used in the DOTS signal channel.
CBOR Key Value:
Key value for the parameter. The key value MUST be an integer in
the 1-65535 range.
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OLD:
+-------------+-------------------------+------------------------+
| Range | Registration Procedures | Note |
+=============+=========================+========================+
| 1-16383 | IETF Review | comprehension-required |
| 16384-32767 | Specification Required | comprehension-optional |
| 32768-49151 | IETF Review | comprehension-optional |
| 49152-65535 | Private Use | comprehension-optional |
+-------------+-------------------------+------------------------+
NEW:
+-------------+-------------------------+------------------------+
| Range | Registration Procedures | Note |
+=============+=========================+========================+
| 1-127 | IETF Review | comprehension-required |
| 128-255 | IETF Review | comprehension-optional |
| 256-16383 | IETF Review | comprehension-required |
| 16384-32767 | Specification Required | comprehension-optional |
| 32768-49151 | IETF Review | comprehension-optional |
| 49152-65535 | Private Use | comprehension-optional |
+-------------+-------------------------+------------------------+
Registration requests for the 16384-32767 range are evaluated
after a three-week review period on the dots-signal-reg-
review@ietf.org mailing list, on the advice of one or more
Designated Experts. However, to allow for the allocation of
values prior to publication, the Designated Experts may approve
registration once they are satisfied that such a specification
will be published. New registration requests should be sent in
the form of an email to the review mailing list; the request
should use an appropriate subject (e.g., "Request to register CBOR
Key Value for DOTS: example"). IANA will only accept new
registrations from the Designated Experts, and it will check that
review was requested on the mailing list in accordance with these
procedures.
Within the review period, the Designated Experts will either
approve or deny the registration request, communicating this
decision to the review list and IANA. Denials should include an
explanation and, if applicable, suggestions as to how to make the
request successful. Registration requests that are undetermined
for a period longer than 21 days can be brought to the IESG's
attention (using the iesg@ietf.org mailing list) for resolution.
Criteria that should be applied by the Designated Experts include
determining whether the proposed registration duplicates existing
functionality, whether it is likely to be of general applicability
or whether it is useful only for a single use case, and whether
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the registration description is clear. IANA must only accept
registry updates to the 16384-32767 range from the Designated
Experts and should direct all requests for registration to the
review mailing list. It is suggested that multiple Designated
Experts be appointed. In cases where a registration decision
could be perceived as creating a conflict of interest for a
particular Expert, that Expert should defer to the judgment of the
other Experts.
CBOR Major Type:
CBOR Major type and optional tag for the parameter.
Change Controller:
For Standards Track RFCs, list the "IESG". For others, give the
name of the responsible party. Other details (e.g., email
address) may also be included.
Specification Document(s):
Reference to the document or documents that specify the parameter,
preferably including URIs that can be used to retrieve copies of
the documents. An indication of the relevant sections may also be
included but is not required.
10.6.1.2. Update Subregistry Content
IANA is requested to update entries in the "0-51" and "49152-65535"
ranges from the "DOTS Signal Channel CBOR Key Values" registry with
the RFC number to be assigned to this document.
10.6.2. Status Codes Subregistry
IANA is requested to update these entries from the "DOTS Signal
Channel Status Codes" registry with the RFC number to be assigned to
this document:
+--------------+---------------+----------------------+-----------+
| Code | Label | Description | Reference |
+==============+===============+======================+===========+
| 0 | Reserved | | [RFCXXXX] |
+--------------+---------------+----------------------+-----------+
| 1 | attack- | Attack mitigation | [RFCXXXX] |
| | mitigation- | setup is in progress | |
| | in-progress | (e.g., changing the | |
| | | network path to | |
| | | redirect the inbound | |
| | | traffic to a DOTS | |
| | | mitigator). | |
+--------------+---------------+----------------------+-----------+
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| 2 | attack- | Attack is being | [RFCXXXX] |
| | successfully- | successfully | |
| | mitigated | mitigated (e.g., | |
| | | traffic is | |
| | | redirected to a DDoS | |
| | | mitigator and attack | |
| | | traffic is dropped). | |
+--------------+---------------+----------------------+-----------+
| 3 | attack- | Attack has stopped | [RFCXXXX] |
| | stopped | and the DOTS client | |
| | | can withdraw the | |
| | | mitigation request. | |
+--------------+---------------+----------------------+-----------+
| 4 | attack- | Attack has exceeded | [RFCXXXX] |
| | exceeded- | the mitigation | |
| | capability | provider capability. | |
+--------------+---------------+----------------------+-----------+
| 5 | dots-client- | DOTS client has | [RFCXXXX] |
| | withdrawn- | withdrawn the | |
| | mitigation | mitigation request | |
| | | and the mitigation | |
| | | is active but | |
| | | terminating. | |
+--------------+---------------+----------------------+-----------+
| 6 | attack- | Attack mitigation is | [RFCXXXX] |
| | mitigation- | now terminated. | |
| | terminated | | |
+--------------+---------------+----------------------+-----------+
| 7 | attack- | Attack mitigation is | [RFCXXXX] |
| | mitigation- | withdrawn. | |
| | withdrawn | | |
+--------------+---------------+----------------------+-----------+
| 8 | attack- | Attack mitigation | [RFCXXXX] |
| | mitigation- | will be triggered | |
| | signal-loss | for the mitigation | |
| | | request only when | |
| | | the DOTS signal | |
| | | channel session is | |
| | | lost. | |
+--------------+---------------+----------------------+-----------+
| 9-2147483647 | Unassigned | | |
+--------------+---------------+----------------------+-----------+
Table 7: Initial DOTS Signal Channel Status Codes
New codes can be assigned via Standards Action [RFC8126].
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10.6.3. Conflict Status Codes Subregistry
IANA is requested to update these entries from the "DOTS Signal
Channel Conflict Status Codes" registry with the RFC number to be
assigned to this document:
+--------------+-------------------+--------------------+-----------+
| Code | Label | Description | Reference |
+==============+===================+====================+===========+
| 0 | Reserved | | [RFCXXXX] |
+--------------+-------------------+--------------------+-----------+
| 1 | request-inactive- | DOTS server | [RFCXXXX] |
| | other-active | has detected | |
| | | conflicting | |
| | | mitigation | |
| | | requests from | |
| | | different DOTS | |
| | | clients. This | |
| | | mitigation | |
| | | request is | |
| | | currently | |
| | | inactive until | |
| | | the conflicts | |
| | | are resolved. | |
| | | Another | |
| | | mitigation | |
| | | request is | |
| | | active. | |
+--------------+-------------------+--------------------+-----------+
| 2 | request-active | DOTS server | [RFCXXXX] |
| | | has detected | |
| | | conflicting | |
| | | mitigation | |
| | | requests from | |
| | | different DOTS | |
| | | clients. This | |
| | | mitigation | |
| | | request is | |
| | | currently | |
| | | active. | |
+--------------+-------------------+--------------------+-----------+
| 3 | all-requests- | DOTS server | [RFCXXXX] |
| | inactive | has detected | |
| | | conflicting | |
| | | mitigation | |
| | | requests from | |
| | | different DOTS | |
| | | clients. All | |
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| | | conflicting | |
| | | mitigation | |
| | | requests are | |
| | | inactive. | |
+--------------+-------------------+--------------------+-----------+
| 4-2147483647 | Unassigned | | |
+--------------+-------------------+--------------------+-----------+
Table 8: Initial DOTS Signal Channel Conflict Status Codes
New codes can be assigned via Standards Action [RFC8126].
10.6.4. Conflict Cause Codes Subregistry
IANA is requested to update these entries from the "DOTS Signal
Channel Conflict Cause Codes" registry with the RFC number to be
assigned to this document:
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+--------------+---------------------+----------------+-----------+
| Code | Label | Description | Reference |
+==============+=====================+================+===========+
| 0 | Reserved | | [RFCXXXX] |
+--------------+---------------------+----------------+-----------+
| 1 | overlapping-targets | Overlapping | [RFCXXXX] |
| | | targets. | |
+--------------+---------------------+----------------+-----------+
| 2 | conflict-with- | Conflicts with | [RFCXXXX] |
| | acceptlist | an existing | |
| | | accept-list. | |
| | | This code is | |
| | | returned when | |
| | | the DDoS | |
| | | mitigation | |
| | | detects source | |
| | | addresses/ | |
| | | prefixes in | |
| | | the accept- | |
| | | listed ACLs | |
| | | are attacking | |
| | | the target. | |
+--------------+---------------------+----------------+-----------+
| 3 | cuid-collision | CUID | [RFCXXXX] |
| | | Collision. | |
| | | This code is | |
| | | returned when | |
| | | a DOTS client | |
| | | uses a 'cuid' | |
| | | that is | |
| | | already used | |
| | | by another | |
| | | DOTS client. | |
+--------------+---------------------+----------------+-----------+
| 4-2147483647 | Unassigned | | |
+--------------+---------------------+----------------+-----------+
Table 9: Initial DOTS Signal Channel Conflict Cause Codes
New codes can be assigned via Standards Action [RFC8126].
10.6.5. Attack Status Codes Subregistry
IANA is requested to update these entries from the "DOTS Signal
Channel Attack Status Codes" registry with the RFC number to be
assigned to this document:
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+--------------+----------------------+-----------------+-----------+
| Code | Label | Description | Reference |
+==============+======================+=================+===========+
| 0 | Reserved | | [RFCXXXX] |
+--------------+----------------------+-----------------+-----------+
| 1 | under-attack | The DOTS | [RFCXXXX] |
| | | client | |
| | | determines | |
| | | that it is | |
| | | still under | |
| | | attack. | |
+--------------+----------------------+-----------------+-----------+
| 2 | attack-successfully- | The DOTS | [RFCXXXX] |
| | mitigated | client | |
| | | determines | |
| | | that the | |
| | | attack is | |
| | | successfully | |
| | | mitigated. | |
+--------------+----------------------+-----------------+-----------+
| 3-2147483647 | Unassigned | | |
+--------------+----------------------+-----------------+-----------+
Table 10: Initial DOTS Signal Channel Attack Status Codes
New codes can be assigned via Standards Action [RFC8126].
10.7. DOTS Signal Channel YANG Modules
IANA already registered the following URIs in the "ns" subregistry
within the "IETF XML Registry" [RFC3688]:
URI: urn:ietf:params:xml:ns:yang:ietf-dots-signal-channel
Registrant Contact: The IESG.
XML: N/A; the requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:iana-dots-signal-channel
Registrant Contact: IANA.
XML: N/A; the requested URI is an XML namespace.
This document requests IANA to update the following YANG modules in
the "YANG Module Names" subregistry [RFC6020] within the "YANG
Parameters" registry.
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Name: ietf-dots-signal-channel
Maintained by IANA: N
Namespace: urn:ietf:params:xml:ns:yang:ietf-dots-signal-channel
Prefix: dots-signal
Reference: RFCXXXX
Name: iana-dots-signal-channel
Maintained by IANA: Y
Namespace: urn:ietf:params:xml:ns:yang:iana-dots-signal-channel
Prefix: iana-dots-signal
Reference: RFCXXXX
This document defines the initial version of the IANA-maintained
iana-dots-signal-channel YANG module. IANA is requested to maintain
this note:
Status, conflict status, conflict cause, and attack status values
must not be directly added to the iana-dots-signal-channel YANG
module. They must instead be respectively added to the "DOTS
Status Codes", "DOTS Conflict Status Codes", "DOTS Conflict Cause
Codes", and "DOTS Attack Status Codes" registries.
When a 'status', 'conflict-status', 'conflict-cause', or 'attack-
status' value is respectively added to the "DOTS Status Codes", "DOTS
Conflict Status Codes", "DOTS Conflict Cause Codes", or "DOTS Attack
Status Codes" registry, a new "enum" statement must be added to the
iana-dots-signal-channel YANG module. The following "enum"
statement, and substatements thereof, should be defined:
"enum": Replicates the label from the registry.
"value": Contains the IANA-assigned value corresponding to the
'status', 'conflict-status', 'conflict-cause', or
'attack-status'.
"description": Replicates the description from the registry.
"reference": Replicates the reference from the registry and adds
the title of the document.
When the iana-dots-signal-channel YANG module is updated, a new
"revision" statement must be added in front of the existing revision
statements.
IANA is requested to update this note of "DOTS Status Codes", "DOTS
Conflict Status Codes", "DOTS Conflict Cause Codes", and "DOTS Attack
Status Codes" registries:
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When this registry is modified, the YANG module iana-dots-signal-
channel must be updated as defined in [RFCXXXX].
11. Security Considerations
High-level DOTS security considerations are documented in [RFC8612]
and [RFC8811].
Authenticated encryption MUST be used for data confidentiality and
message integrity. The interaction between the DOTS agents requires
Datagram Transport Layer Security (DTLS) or Transport Layer Security
(TLS) with a cipher suite offering confidentiality protection, and
the guidance given in [RFC7525] MUST be followed to avoid attacks on
(D)TLS. The (D)TLS protocol profile used for the DOTS signal channel
is specified in Section 7.
If TCP is used between DOTS agents, an attacker may be able to inject
RST packets, bogus application segments, etc., regardless of whether
TLS authentication is used. Because the application data is TLS
protected, this will not result in the application receiving bogus
data, but it will constitute a DoS on the connection. This attack
can be countered by using TCP Authentication Option (TCP-AO)
[RFC5925]. Although not widely adopted, if TCP-AO is used, then any
bogus packets injected by an attacker will be rejected by the TCP-AO
integrity check and therefore will never reach the TLS layer.
If the 'cuid' is guessable, a misbehaving DOTS client from within the
client's domain can use the 'cuid' of another DOTS client of the
domain to delete or alter active mitigations. For this attack to
succeed, the misbehaving client's messages need to pass the security
validation checks by the DOTS server and, if the communication
involves a client-domain DOTS gateway, the security checks of that
gateway.
A similar attack can be achieved by a compromised DOTS client that
can sniff the TLS 1.2 handshake, use the client certificate to
identify the 'cuid' used by another DOTS client. This attack is not
possible if algorithms such as version 4 Universally Unique
IDentifiers (UUIDs) in Section 4.4 of [RFC4122] are used to generate
the 'cuid' because such UUIDs are not a deterministic function of the
client certificate. Likewise, this attack is not possible with TLS
1.3 because most of the TLS handshake is encrypted and the client
certificate is not visible to eavesdroppers.
A compromised DOTS client can collude with a DDoS attacker to send a
mitigation request for a target resource, get the mitigation efficacy
from the DOTS server, and convey the mitigation efficacy to the DDoS
attacker to possibly change the DDoS attack strategy. Obviously,
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signaling an attack by the compromised DOTS client to the DOTS server
will trigger attack mitigation. This attack can be prevented by
monitoring and auditing DOTS clients to detect misbehavior and to
deter misuse, and by only authorizing the DOTS client to request
mitigation for specific target resources (e.g., an application server
is authorized to request mitigation for its IP addresses, but a DDoS
mitigator can request mitigation for any target resource in the
network). Furthermore, DOTS clients are typically co-located on
network security services (e.g., firewall), and a compromised
security service potentially can do a lot more damage to the network.
Rate-limiting DOTS requests, including those with new 'cuid' values,
from the same DOTS client defend against DoS attacks that would
result in varying the 'cuid' to exhaust DOTS server resources. Rate-
limit policies SHOULD be enforced on DOTS gateways (if deployed) and
DOTS servers.
In order to prevent leaking internal information outside a client's
domain, DOTS gateways located in the client domain SHOULD NOT reveal
the identification information that pertains to internal DOTS clients
(e.g., source IP address, client's hostname) unless explicitly
configured to do so.
DOTS servers MUST verify that requesting DOTS clients are entitled to
trigger actions on a given IP prefix. A DOTS server MUST NOT
authorize actions due to a DOTS client request unless those actions
are limited to that DOTS client's domain IP resources. The exact
mechanism for the DOTS servers to validate that the target prefixes
are within the scope of the DOTS client domain is deployment
specific.
The presence of DOTS gateways may lead to infinite forwarding loops,
which is undesirable. To prevent and detect such loops, this
document uses the Hop-Limit Option.
When FQDNs are used as targets, the DOTS server MUST rely upon DNS
privacy-enabling protocols (e.g., DNS over TLS [RFC7858] or DNS over
HTTPS (DoH) [RFC8484]) to prevent eavesdroppers from possibly
identifying the target resources protected by the DDoS mitigation
service to ensure the target FQDN resolution is authentic (e.g.,
DNSSEC [RFC4034]).
CoAP-specific security considerations are discussed in Section 11 of
[RFC7252], while CBOR-related security considerations are discussed
in Section 10 of [RFC8949].
This document defines YANG data structures that are meant to be used
as an abstract representation of DOTS signal channel messages. As
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such, the "ietf-dots-signal-channel" module does not introduce any
new vulnerabilities beyond those specified above.
12. References
12.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[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>.
[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>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
[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>.
[RFC4279] Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key
Ciphersuites for Transport Layer Security (TLS)",
RFC 4279, DOI 10.17487/RFC4279, December 2005,
<https://www.rfc-editor.org/info/rfc4279>.
[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>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.
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[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
Extensions: Extension Definitions", RFC 6066,
DOI 10.17487/RFC6066, January 2011,
<https://www.rfc-editor.org/info/rfc6066>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <https://www.rfc-editor.org/info/rfc6125>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC6991, July 2013,
<https://www.rfc-editor.org/info/rfc6991>.
[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
June 2014, <https://www.rfc-editor.org/info/rfc7250>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
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[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<https://www.rfc-editor.org/info/rfc7641>.
[RFC7918] Langley, A., Modadugu, N., and B. Moeller, "Transport
Layer Security (TLS) False Start", RFC 7918,
DOI 10.17487/RFC7918, August 2016,
<https://www.rfc-editor.org/info/rfc7918>.
[RFC7924] Santesson, S. and H. Tschofenig, "Transport Layer Security
(TLS) Cached Information Extension", RFC 7924,
DOI 10.17487/RFC7924, July 2016,
<https://www.rfc-editor.org/info/rfc7924>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
the Constrained Application Protocol (CoAP)", RFC 7959,
DOI 10.17487/RFC7959, August 2016,
<https://www.rfc-editor.org/info/rfc7959>.
[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>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2:
Better Connectivity Using Concurrency", RFC 8305,
DOI 10.17487/RFC8305, December 2017,
<https://www.rfc-editor.org/info/rfc8305>.
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[RFC8323] Bormann, C., Lemay, S., Tschofenig, H., Hartke, K.,
Silverajan, B., and B. Raymor, Ed., "CoAP (Constrained
Application Protocol) over TCP, TLS, and WebSockets",
RFC 8323, DOI 10.17487/RFC8323, February 2018,
<https://www.rfc-editor.org/info/rfc8323>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/info/rfc8615>.
[RFC8768] Boucadair, M., Reddy.K, T., and J. Shallow, "Constrained
Application Protocol (CoAP) Hop-Limit Option", RFC 8768,
DOI 10.17487/RFC8768, March 2020,
<https://www.rfc-editor.org/info/rfc8768>.
[RFC8783] Boucadair, M., Ed. and T. Reddy.K, Ed., "Distributed
Denial-of-Service Open Threat Signaling (DOTS) Data
Channel Specification", RFC 8783, DOI 10.17487/RFC8783,
May 2020, <https://www.rfc-editor.org/info/rfc8783>.
[RFC8791] Bierman, A., Bjoerklund, M., and K. Watsen, "YANG Data
Structure Extensions", RFC 8791, DOI 10.17487/RFC8791,
June 2020, <https://www.rfc-editor.org/info/rfc8791>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
12.2. Informative References
[I-D.boucadair-dots-earlydata]
Boucadair, M. and T. Reddy, "Using Early Data in DOTS",
draft-boucadair-dots-earlydata-00 (work in progress),
January 2019.
[I-D.ietf-core-comi]
Veillette, M., Stok, P. V. D., Pelov, A., Bierman, A., and
I. Petrov, "CoAP Management Interface (CORECONF)", draft-
ietf-core-comi-11 (work in progress), January 2021.
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[I-D.ietf-core-yang-cbor]
Veillette, M., Petrov, I., and A. Pelov, "CBOR Encoding of
Data Modeled with YANG", draft-ietf-core-yang-cbor-15
(work in progress), January 2021.
[I-D.ietf-dots-multihoming]
Boucadair, M., Reddy, T., and W. Pan, "Multi-homing
Deployment Considerations for Distributed-Denial-of-
Service Open Threat Signaling (DOTS)", draft-ietf-dots-
multihoming-05 (work in progress), November 2020.
[I-D.ietf-dots-telemetry]
Boucadair, M., Reddy, T., Doron, E., Chen, M., and J.
Shallow, "Distributed Denial-of-Service Open Threat
Signaling (DOTS) Telemetry", draft-ietf-dots-telemetry-15
(work in progress), December 2020.
[I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", draft-ietf-tls-dtls13-43 (work in progress), April
2021.
[IANA-CBOR-Tags]
IANA, "Concise Binary Object Representation (CBOR) Tags",
<https://www.iana.org/assignments/cbor-tags/cbor-
tags.xhtml>.
[IANA-CoAP-Content-Formats]
IANA, "CoAP Content-Formats",
<https://www.iana.org/assignments/core-parameters/core-
parameters.xhtml#content-formats>.
[IANA-MediaTypes]
IANA, "Media Types",
<https://www.iana.org/assignments/media-types>.
[IANA-Proto]
IANA, "Protocol Numbers", 2011,
<https://www.iana.org/assignments/protocol-numbers>.
[REG-DOTS]
IANA, "Distributed Denial-of-Service Open Threat Signaling
(DOTS) Signal Channel",
<https://www.iana.org/assignments/dots/dots.xhtml>.
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[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022,
DOI 10.17487/RFC3022, January 2001,
<https://www.rfc-editor.org/info/rfc3022>.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, DOI 10.17487/RFC4034, March 2005,
<https://www.rfc-editor.org/info/rfc4034>.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<https://www.rfc-editor.org/info/rfc4122>.
[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram
Congestion Control Protocol (DCCP)", RFC 4340,
DOI 10.17487/RFC4340, March 2006,
<https://www.rfc-editor.org/info/rfc4340>.
[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>.
[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, <https://www.rfc-editor.org/info/rfc4787>.
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<https://www.rfc-editor.org/info/rfc4960>.
[RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common
Mitigations", RFC 4987, DOI 10.17487/RFC4987, August 2007,
<https://www.rfc-editor.org/info/rfc4987>.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <https://www.rfc-editor.org/info/rfc5925>.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
DOI 10.17487/RFC6052, October 2010,
<https://www.rfc-editor.org/info/rfc6052>.
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[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.
[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and SHA-based HMAC and HKDF)", RFC 6234,
DOI 10.17487/RFC6234, May 2011,
<https://www.rfc-editor.org/info/rfc6234>.
[RFC6296] Wasserman, M. and F. Baker, "IPv6-to-IPv6 Network Prefix
Translation", RFC 6296, DOI 10.17487/RFC6296, June 2011,
<https://www.rfc-editor.org/info/rfc6296>.
[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
<https://www.rfc-editor.org/info/rfc6724>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>.
[RFC6887] Wing, D., Ed., Cheshire, S., Boucadair, M., Penno, R., and
P. Selkirk, "Port Control Protocol (PCP)", RFC 6887,
DOI 10.17487/RFC6887, April 2013,
<https://www.rfc-editor.org/info/rfc6887>.
[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, <https://www.rfc-editor.org/info/rfc6888>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<https://www.rfc-editor.org/info/rfc7030>.
[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
<https://www.rfc-editor.org/info/rfc7413>.
[RFC7452] Tschofenig, H., Arkko, J., Thaler, D., and D. McPherson,
"Architectural Considerations in Smart Object Networking",
RFC 7452, DOI 10.17487/RFC7452, March 2015,
<https://www.rfc-editor.org/info/rfc7452>.
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[RFC7589] Badra, M., Luchuk, A., and J. Schoenwaelder, "Using the
NETCONF Protocol over Transport Layer Security (TLS) with
Mutual X.509 Authentication", RFC 7589,
DOI 10.17487/RFC7589, June 2015,
<https://www.rfc-editor.org/info/rfc7589>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG",
RFC 7951, DOI 10.17487/RFC7951, August 2016,
<https://www.rfc-editor.org/info/rfc7951>.
[RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
<https://www.rfc-editor.org/info/rfc8340>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>.
[RFC8489] Petit-Huguenin, M., Salgueiro, G., Rosenberg, J., Wing,
D., Mahy, R., and P. Matthews, "Session Traversal
Utilities for NAT (STUN)", RFC 8489, DOI 10.17487/RFC8489,
February 2020, <https://www.rfc-editor.org/info/rfc8489>.
[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>.
[RFC8612] Mortensen, A., Reddy, T., and R. Moskowitz, "DDoS Open
Threat Signaling (DOTS) Requirements", RFC 8612,
DOI 10.17487/RFC8612, May 2019,
<https://www.rfc-editor.org/info/rfc8612>.
[RFC8782] Reddy.K, T., Ed., Boucadair, M., Ed., Patil, P.,
Mortensen, A., and N. Teague, "Distributed Denial-of-
Service Open Threat Signaling (DOTS) Signal Channel
Specification", RFC 8782, DOI 10.17487/RFC8782, May 2020,
<https://www.rfc-editor.org/info/rfc8782>.
[RFC8811] Mortensen, A., Ed., Reddy.K, T., Ed., Andreasen, F.,
Teague, N., and R. Compton, "DDoS Open Threat Signaling
(DOTS) Architecture", RFC 8811, DOI 10.17487/RFC8811,
August 2020, <https://www.rfc-editor.org/info/rfc8811>.
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[RFC8903] Dobbins, R., Migault, D., Moskowitz, R., Teague, N., Xia,
L., and K. Nishizuka, "Use Cases for DDoS Open Threat
Signaling", RFC 8903, DOI 10.17487/RFC8903, May 2021,
<https://www.rfc-editor.org/info/rfc8903>.
[RFC8973] Boucadair, M. and T. Reddy.K, "DDoS Open Threat Signaling
(DOTS) Agent Discovery", RFC 8973, DOI 10.17487/RFC8973,
January 2021, <https://www.rfc-editor.org/info/rfc8973>.
[URI] IANA, "Well-Known URIs",
<https://www.iana.org/assignments/well-known-uris/well-
known-uris.xhtml>.
Appendix A. Summary of Changes From RFC8782
The main changes compared to [RFC8782] are as follows:
o Update the "ietf-dots-signal-channel" YANG module (Section 5.3)
and the tree structure (Section 5.1) to follow the new YANG data
structure specified in [RFC8791]. In particular:
* Add in 'choice' to indicate the communication direction in
which a data node applies. If no 'choice' is indicated, a data
node can appear in both directions (i.e., from DOTS clients to
DOTS servers and vice versa).
* Remove 'config' clauses. Note that 'config' statements will be
ignored (if present) anyway according to Section 4 of
[RFC8791]. This supersedes the references to the use of 'ro'
and 'rw' which are now covered by 'choice' above.
* Remove 'cuid', 'cdid', and 'sid' data nodes from the structure
because these data nodes are included as Uri-Path options, not
within the message body.
* Remove the list keys for the mitigation scope message type
(i.e., 'cuid' and 'mid'). 'mid' is not indicated as a key
because it is included as Uri-Path option for requests and in
the message body for responses. Note that Section 4 of
[RFC8791] specifies that a list does not require to have a key
statement defined.
o Add a new section with a summary of the error code responses that
can be returned by a DOTS server (Section 9).
o Update the IANA section to allocate a new range for comprehension-
optional attributes (Section 10.6.1.1). This modification is
motivated by the need to allow for compact DOTS signal messages
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that include a long list of comprehension-optional attributes,
e.g., DOTS telemetry messages [I-D.ietf-dots-telemetry].
o Add Appendix C to list recommended/default values of key DOTS
signal channel parameters.
o Add subsections to Section 4.4.1 for better readability.
Appendix B. CUID Generation
The document recommends the use of SPKI to generate the 'cuid'. This
design choice is motivated by the following reasons:
o SPKI is globally unique.
o It is deterministic.
o It allows the avoidance of extra cycles that may be induced by
'cuid' collision.
o DOTS clients do not need to store the 'cuid' in a persistent
storage.
o It allows the detection of compromised DOTS clients that do not
adhere to the 'cuid' generation algorithm.
Appendix C. Summary of Protocol Recommended/Default Values
+--------------------------------+---------------------------+
| Parameter | Recommended/Default Value |
+--------------------------------+---------------------------+
| Port number | 4646 (tcp/udp) |
| lifetime | 3600 seconds |
| active-but-terminating | 120 seconds |
| maximum active-but-terminating | 300 seconds |
| heartbeat-interval | 30 seconds |
| minimum 'heartbeat-interval' | 15 seconds |
| maximum 'heartbeat-interval' | 240 seconds |
| missing-hb-allowed | 15 |
| max-retransmit | 3 |
| ack-timeout | 2 seconds |
| ack-random-factor | 1.5 |
| probing-rate | 5 bytes/second |
| trigger-mitigation | true |
+--------------------------------+---------------------------+
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Appendix D. Acknowledgements
Many thanks to Martin Bjoerklund for the suggestion to use RFC8791.
Thanks to Valery Smyslov for the comments, guidance, and support.
Thanks to Ebben Aries for the yangdoctors review, Dan Romascanu for
the opsdir review, Michael Tuexen for the tsv-art review, Dale Worley
for the genart review, and Donald Eastlake for the secdir review.
Thanks to Benjamin Kaduk for the AD review.
Thanks to Martin Duke, Lars Eggert, Erik Kline, Murray Kucherawy,
Eric Vyncke, and Robert Wilton for the IESG review.
D.1. Acknowledgements from RFC8782
Thanks to Christian Jacquenet, Roland Dobbins, Roman Danyliw, Michael
Richardson, Ehud Doron, Kaname Nishizuka, Dave Dolson, Liang Xia,
Gilbert Clark, Xialiang Frank, Jim Schaad, Klaus Hartke, Nesredien
Suleiman, Stephen Farrell, and Yoshifumi Nishida for the discussion
and comments.
The authors would like to give special thanks to Kaname Nishizuka and
Jon Shallow for their efforts in implementing the protocol and
performing interop testing at IETF Hackathons.
Thanks to the core WG for the recommendations on Hop-Limit and
redirect signaling.
Special thanks to Benjamin Kaduk for the detailed AD review.
Thanks to Alexey Melnikov, Adam Roach, Suresh Krishnan, Mirja
Kuehlewind, and Alissa Cooper for the review.
Thanks to Carsten Bormann for his review of the DOTS heartbeat
mechanism.
Appendix E. Contributors
E.1. Authors of RFC8782
The authors of RFC8782 are listed below:
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Tirumaleswar Reddy.K (editor)
McAfee, Inc.
Embassy Golf Link Business Park
Bangalore 560071
Karnataka
India
Email: kondtir@gmail.com
Mohamed Boucadair (editor)
Orange
35000 Rennes
France
Email: mohamed.boucadair@orange.com
Prashanth Patil
Cisco Systems, Inc.
Email: praspati@cisco.com
Andrew Mortensen
Arbor Networks, Inc.
2727 S. State Street
Ann Arbor, MI 48104
United States of America
Email: andrew@moretension.com
Nik Teague
Iron Mountain Data Centers
United Kingdom
Email: nteague@ironmountain.co.uk
E.2. Contributors to RFC8782
The following individuals have contributed to RFC8782:
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Jon Shallow
NCC Group
Email: jon.shallow@nccgroup.trust
Mike Geller
Cisco Systems, Inc.
FL 33309
United States of America
Email: mgeller@cisco.com
Robert Moskowitz
HTT Consulting
Oak Park, MI 42837
United States of America
Email: rgm@htt-consult.com
Authors' Addresses
Mohamed Boucadair (editor)
Orange
Rennes 35000
France
Email: mohamed.boucadair@orange.com
Jon Shallow
United Kingdom
Email: supjps-ietf@jpshallow.com
Tirumaleswar Reddy.K
McAfee, Inc.
Embassy Golf Link Business Park
Bangalore, Karnataka 560071
India
Email: kondtir@gmail.com
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