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Internet Engineering Task Force (IETF) T. Reddy.K
Request for Comments: 9066 Akamai
Category: Standards Track M. Boucadair, Ed.
ISSN: 2070-1721 Orange
J. Shallow
December 2021
Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal
Channel Call Home
Abstract
This document specifies the Denial-of-Service Open Threat Signaling
(DOTS) signal channel Call Home, which enables a Call Home DOTS
server to initiate a secure connection to a Call Home DOTS client and
to receive attack traffic information from the Call Home DOTS client.
The Call Home DOTS server in turn uses the attack traffic information
to identify compromised devices launching outgoing DDoS attacks and
take appropriate mitigation action(s).
The DOTS signal channel Call Home is not specific to home networks;
the solution targets any deployment in which it is required to block
DDoS attack traffic closer to the source(s) of a DDoS attack.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9066.
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 Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
Table of Contents
1. Introduction
2. Terminology
3. Applicability Scope
4. Coexistence of a Base DOTS Signal Channel and DOTS Call Home
5. DOTS Signal Channel Call Home
5.1. Procedure
5.2. DOTS Signal Channel Variations
5.2.1. Heartbeat Mechanism
5.2.2. Redirected Signaling
5.3. DOTS Signal Channel Extension
5.3.1. Mitigation Request
5.3.2. Address Sharing Considerations
6. DOTS Signal Call Home YANG Module
6.1. Tree Structure
6.2. YANG/JSON Mapping Parameters to CBOR
6.3. YANG Module
7. IANA Considerations
7.1. DOTS Signal Channel CBOR Mappings Registry
7.2. New DOTS Conflict Cause
7.3. DOTS Signal Call Home YANG Module
8. Security Considerations
9. Privacy Considerations
10. References
10.1. Normative References
10.2. Informative References
Appendix A. Some Home Network Issues
Appendix B. Disambiguating Base DOTS Signal vs. DOTS Call Home
Acknowledgements
Contributors
Authors' Addresses
1. Introduction
The Distributed Denial-of-Service Open Threat Signaling (DOTS) signal
channel protocol [RFC9132] is used to carry information about a
network resource or a network (or a part thereof) that is under a
Distributed Denial-of-Service (DDoS) attack [RFC4732]. Such
information is sent by a DOTS client to one or multiple DOTS servers
so that appropriate mitigation actions are undertaken on traffic
deemed suspicious. Various use cases are discussed in [RFC8903].
However, [RFC9132] only covers how to mitigate when being attacked
(i.e., protecting a network from inbound DDoS attacks). It does not
cover how to control the attacks close to their source(s) that are
misusing network resources (i.e., outbound DDoS attacks). In
particular, the DOTS signal protocol does not discuss cooperative
DDoS mitigation between the network hosting an attack source and the
Internet Service Provider (ISP) to suppress the outbound DDoS attack
traffic originating from that network. As a reminder, the base basic
DOTS architecture is depicted in Figure 1 (Section 2 of [RFC8811]).
+-----------+ +-------------+
| Mitigator | ~~~~~~~~~~ | DOTS Server |
+-----------+ +-------------+
|
|
|
+---------------+ +-------------+
| Attack Target | ~~~~~~ | DOTS Client |
+---------------+ +-------------+
Figure 1: Basic DOTS Architecture
Appendix A details why the rise of Internet of Things (IoT) compounds
the possibility of these being used as malicious actors that need to
be controlled. Similar issues can be encountered in enterprise
networks, data centers, etc. The ISP offering a DDoS mitigation
service can detect outgoing DDoS attack traffic originating from its
subscribers, or the ISP may receive filtering rules (e.g., using BGP
Flowspec [RFC8955] [RFC8956]) from a transit provider to filter,
block, or rate-limit DDoS attack traffic originating from the ISP's
subscribers to a downstream target. Nevertheless, the DOTS signal
channel does not provide means for the ISP to request blocking such
attacks close to the sources without altering legitimate traffic.
This document fills that void by specifying an extension to the DOTS
signal channel: DOTS signal channel Call Home.
Note: Another design approach would be to extend the DOTS signal
channel with a new attribute to explicitly indicate whether a
mitigation request concerns an outbound DDoS attack. In such an
approach, it is assumed that a DOTS server is deployed within the
domain that is hosting the attack source(s), while a DOTS client
is enabled within an upstream network (e.g., access network).
However, initiating a DOTS signal channel from an upstream network
to a source network is complicated because of the presence of
translators and firewalls. Moreover, the use of the same signal
channel to handle both inbound and outbound attacks complicates
both the heartbeat and redirection mechanisms that are executed as
a function of the attack direction (see Sections 5.2.1 and 5.2.2).
Also, the DOTS server will be subject to fingerprinting (e.g.,
using scanning tools) and DoS attacks (e.g., by having the DOTS
server perform computationally expensive operations). Various
management and deployment considerations that motivate the Call
Home functionality are listed in Section 1.1 of [RFC8071].
"DOTS signal channel Call Home" (or "DOTS Call Home" for short)
refers to a DOTS signal channel established at the initiative of a
DOTS server thanks to a role reversal at the (D)TLS layer
(Section 5.1). That is, the DOTS server initiates a secure
connection to a DOTS client and uses that connection to receive the
attack traffic information (e.g., attack sources) from the DOTS
client.
A high-level DOTS Call Home functional architecture is shown in
Figure 2. Attack source(s) are within the DOTS server domain.
Scope
+.-.-.-.-.-.-.-.-.-.-.-.+
+---------------+ : +-------------+ :
| Alert | ~~~:~~~ | Call Home | :
| | : | DOTS client | :
+---------------+ : +------+------+ :
: | :
: | :
: | :
+---------------+ : +------+------+ :
| Attack | ~~~:~~~ | Call Home | :
| Source(s) | : | DOTS server | :
+---------------+ : +-------------+ :
+.-.-.-.-.-.-.-.-.-.-.-.+
Figure 2: Basic DOTS Signal Channel Call Home Functional Architecture
DOTS agents involved in the DOTS Call Home otherwise adhere to the
DOTS roles as defined in [RFC8612]. For clarity, this document uses
"Call Home DOTS client" (or "Call Home DOTS server") to refer to a
DOTS client (or DOTS server) deployed in a Call Home scenario
(Figure 2). Call Home DOTS agents may (or may not) be co-located
with DOTS agents that are compliant with [RFC9132] (see Section 4 for
more details).
A Call Home DOTS client relies upon a variety of triggers to make use
of the Call Home function (e.g., scrubbing the traffic from the
attack source or receiving an alert from an attack target, a peer
DDoS Mitigation System (DMS), or a transit provider). The definition
of these triggers is deployment specific. It is therefore out of the
scope of this document to elaborate on how these triggers are made
available to a Call Home DOTS client.
In a typical deployment scenario, the Call Home DOTS server is
enabled on a Customer Premises Equipment (CPE), which is aligned with
recent trends to enrich the CPE with advanced security features. For
example, the DOTS Call Home service can be part of services supported
by an ISP-managed CPE or a managed security service subscribed to by
the user. Unlike classic DOTS deployments [RFC8903], a Call Home
DOTS server maintains a single DOTS signal channel session for each
DOTS-capable upstream provisioning domain [DOTS-MULTIHOMING].
For instance, the Call Home DOTS server in the home network initiates
the signal channel Call Home in "idle" time; subsequently, the Call
Home DOTS client in the ISP environment can initiate a mitigation
request whenever the ISP detects there is an attack from a
compromised device in the DOTS server domain (i.e., from within the
home network).
The Call Home DOTS server uses the DDoS attack traffic information to
identify the compromised device in its domain that is responsible for
launching the DDoS attack, optionally notifies a network
administrator, and takes appropriate mitigation action(s). For
example, a mitigation action can be to quarantine the compromised
device or block its traffic to the attack target(s) until the
mitigation request is withdrawn.
This document assumes that Call Home DOTS servers are provisioned
with a way to know how to reach the upstream Call Home DOTS
client(s), which could occur by a variety of means (e.g., [RFC8973]).
The specification of such means are out of scope of this document.
More information about the applicability scope of the DOTS signal
channel Call Home is provided in Section 3.
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.
The reader should be familiar with the terms defined in Section 1.2
of [RFC8612].
"DDoS Mitigation System (DMS)" refers to a system that performs DDoS
mitigation.
"Base DOTS signal channel" refers to [RFC9132].
The meaning of the symbols in YANG tree diagrams are defined in
[RFC8340] and [RFC8791].
(D)TLS is used for statements that apply to both Transport Layer
Security (TLS) [RFC8446] and Datagram Transport Layer Security (DTLS)
[RFC6347] [DTLS13]. Specific terms are used for any statement that
applies to either protocol alone.
3. Applicability Scope
The problems discussed in Section 1 may be encountered in many
deployments (e.g., home networks, enterprise networks, transit
networks, data centers). The solution specified in this document can
be used for those deployments to block DDoS attack traffic closer to
the source(s) of the attack. That is, attacks that are issued, e.g.,
from within an enterprise network or a data center will thus be
blocked before exiting these networks.
An instantiation of the Call Home functional architecture is depicted
in Figure 3.
+-------------+
|Attack Target|
+-----+-------+
| /\ Target Network
......................|.||....................
.--------+-||-------.
( || )-.
.' || '
( Internet || )
( || -'
'-( || )
'------+-||---------'
......................|.||.....................
.--------+-||-------. Network
( || )-. Provider
.' Call Home || ' (DMS)
( DOTS client || )
( || -'
'-( || )
'------+-||---------'
......................|.||.......................
.--------+-||-------. Source Network
( || )-.
.' Call Home || '
( DOTS server || Outbound )
( || DDoS -'
'-( || Attack )
'------+-||---------'
| ||
+-----+-++----+
|Attack Source|
+-------------+
Figure 3: DOTS Signal Channel Call Home Reference Architecture
It is out of the scope of this document to identify an exhaustive
list of such deployments.
Call Home DOTS agent relationships are similar to those discussed in
Section 2.3 of [RFC8811]. For example, multiple Call Home DOTS
servers of the same domain can be associated with the same Call Home
DOTS client. A Call Home DOTS client may decide to contact these
Call Home DOTS servers sequentially, fork a mitigation request to all
of them, or select one Call Home DOTS server to place a mitigation
request. Such a decision is implementation specific.
For some mitigations, feedback may be required from an administrator
to confirm a filtering action. The means to seek an administrator's
consent are deployment specific. Indeed, a variety of implementation
options can be considered for any given Call Home DOTS deployment,
such as push notifications using a dedicated application, Syslog,
etc. It is out of the scope of this document to make recommendations
about how such interactions are implemented (see Figure 2).
The Call Home DOTS server can be enabled on a border router or a
dedicated appliance. For the particular case of home networks, the
Call Home DOTS server functionality can be enabled on a managed CPE
or bundled with a CPE management application that is provided by an
ISP to its subscribers. These managed services are likely to be
designed to hide the complexity of managing (including configuring)
the CPE. For example, managed CPEs support the means to notify the
user when a new device is detected in order to seek confirmation as
to whether or not access should be granted to the device. These
means can be upgraded to interface with the Call Home DOTS server.
Customized settings can be configured by users to control the
notifications (e.g., triggers, type) and default actions.
4. Coexistence of a Base DOTS Signal Channel and DOTS Call Home
The DOTS signal channel Call Home does not require or preclude the
activation of the base DOTS signal channel [RFC9132]. Some sample
deployment schemes are discussed in this section for illustration
purposes.
The network that hosts an attack source may also be subject to
inbound DDoS attacks. In that case, both the base DOTS signal
channel and DOTS signal channel Call Home may be enabled as shown in
Figure 4 (same DMS provider) or Figure 5 (distinct DMS providers).
DOTS Signal Channel Base DOTS
Call Home Signal Channel
+-.-.-.-.-.-.-.-.-.-++-.-.-.-.-.-.-.-.-.-+
: +------+ :: +------+ :
: | DOTS | :: | DOTS | :
: |client| :: |server| :
: +--+---+ :: +---+--+ :
: /\ | :: | : Network
: || | :: | :Provider
: || | :: | : (DMS)
...:.....||......|.....::.....|.............:........
Outbound || | :: | || Inbound
DDoS || | :: | || DDoS
Attack || | :: | \/ Attack
: +--+---+ :: +---+--+ :
: | DOTS | :: | DOTS | :
: |server| :: |client| :
: +------+ :: +------+ :
+-.-.-.-.-.-.-.-.-.-++-.-.-.-.-.-.-.-.-.-+
Network #A
Figure 4: Activation of a Base DOTS Signal Channel and Call Home
(Same DMS Provider)
Note that a DMS provider may not be on the default forwarding path of
inbound DDoS attack traffic targeting a network (e.g., Network #B in
Figure 5). Nevertheless, the DOTS signal channel Call Home requires
the DMS provider to be on the default forwarding path of the outbound
traffic from a given network.
DOTS Signal Channel Base DOTS
Call Home Signal Channel
+-.-.-.-.-.-.-.-.-.-++-.-.-.-.-.-.-.-.-.-+
: Network +------+ :: +------+ Third :
: Provider | DOTS | :: | DOTS | Party :
: (DMS) |client| :: |server| DMS :
: +--+---+ :: +---+--+ Provider :
: /\ | :: | :
: || | :: | :
: || | :: | :
...:.....||......|.....::.....|.............:........
Outbound || | :: | || Inbound
DDoS || | :: | || DDoS
Attack || | :: | \/ Attack
: +--+---+ :: +---+--+ :
: | DOTS | :: | DOTS | :
: |server| :: |client| :
: +------+ :: +------+ :
+-.-.-.-.-.-.-.-.-.-++-.-.-.-.-.-.-.-.-.-+
Network #B
Figure 5: Activation of a Base DOTS Signal Channel and Call Home
(Distinct DMS Providers)
Figures 6 and 7 depict examples where the same node embeds both base
DOTS and Call Home DOTS agents. For example, a DOTS server and a
Call Home DOTS client may be enabled on the same device within the
infrastructure of a DMS provider (e.g., Node #i in Figure 6), or a
DOTS client and a Call Home DOTS server may be enabled on the same
device within a source network (e.g., Node #j with Network #D shown
in Figure 7).
Whether the same or distinct nodes are used to host base DOTS and
Call Home DOTS agents is specific to each domain.
DOTS Signal Channel Base DOTS
Call Home Signal Channel
+-.-.-.-.-.-.-.-.-.-++-.-.-.-.-.-.-.-.-.-+
: +----------------------+ :
: | Node #i | :
: | +------+ +------+ | :
: | | DOTS | | DOTS | | :
: | |client| |server| | :
: | +--+---+ +---+--+ | :
: +----|-----::-----|----+ : Network
: /\ | :: | :Provider
: || | :: | : (DMS)
...:.....||......|.....::.....|.............:........
Outbound || | :: | || Inbound
DDoS || | :: | || DDoS
Attack || | :: | \/ Attack
: +--+---+ :: +---+--+ :
: | DOTS | :: | DOTS | :
: |server| :: |client| :
: +------+ :: +------+ :
+-.-.-.-.-.-.-.-.-.-++-.-.-.-.-.-.-.-.-.-+
Network #C
Figure 6: The Same Node Embedding a Call Home DOTS Client and a
DOTS Server at the Network Provider's Side
DOTS Signal Channel Base DOTS
Call Home Signal Channel
+-.-.-.-.-.-.-.-.-.-++-.-.-.-.-.-.-.-.-.-+
: +----------------------+ :
: | Node #k | :
: | +------+ +------+ | :
: | | DOTS | | DOTS | | :
: | |client| |server| | :
: | +--+---+ +---+--+ | :
: +----|-----::-----|----+ : Network
: /\ | :: | :Provider
: || | :: | : (DMS)
...:.....||......|.....::.....|.............:........
Outbound || | :: | || Inbound
DDoS || | :: | || DDoS
Attack || | :: | \/ Attack
: +----|-----::-----|----+ :
: | +--+---+ +---+--+ | :
: | | DOTS | | DOTS | | :
: | |server| |client| | :
: | +------+ +------+ | :
: | Node #j | :
: +----------------------+ :
+-.-.-.-.-.-.-.-.-.-++-.-.-.-.-.-.-.-.-.-+
Network #D
Figure 7: The Same Node Embedding both a DOTS Client and a Call
Home DOTS Server
Appendix B elaborates on the considerations to unambiguously
distinguish DOTS messages that belong to each of these channels.
5. DOTS Signal Channel Call Home
5.1. Procedure
The DOTS signal channel Call Home preserves all but one of the DOTS
client/server roles in the DOTS protocol stack, as compared to the
client-initiated DOTS signal channel protocol [RFC9132]. The role
reversal that occurs is at the (D)TLS layer; that is, (1) the Call
Home DOTS server acts as a DTLS client, and the Call Home DOTS client
acts as a DTLS server; or (2) the Call Home DOTS server acts as a TLS
client initiating the underlying TCP connection, and the Call Home
DOTS client acts as a TLS server. The Call Home DOTS server
initiates a (D)TLS handshake to the Call Home DOTS client.
For example, a home network element (e.g., home router) co-located
with a Call Home DOTS server is the (D)TLS client. That is, the Call
Home DOTS server assumes the role of the (D)TLS client, but the
network element's role as a DOTS server remains the same.
Existing certificate chains and mutual authentication mechanisms
between the DOTS agents are unaffected by the Call Home function.
From a deployment standpoint, and given the scale of Call Home DOTS
servers that may be involved, enabling means for automating the
provisioning of credentials on Call Home DOTS servers to authenticate
to the Call Home DOTS client is encouraged. It is out of the scope
of this document to elaborate on these means.
Figure 8 illustrates a sample DOTS Call Home flow exchange:
+-----------+ +-----------+
| Call Home | | Call Home |
| DOTS | | DOTS |
| server | | client |
+-----+-----+ +-----+-----+
(D)TLS client (D)TLS server
| |
| 1. (D)TLS connection |
|----------------------------------->|
| 2. Mitigation request |
|<-----------------------------------|
| ... |
Figure 8: DOTS Signal Channel Call Home Sequence Diagram
The DOTS signal channel Call Home procedure is as follows:
1. If UDP transport is used, the Call Home DOTS server begins by
initiating a DTLS connection to the Call Home DOTS client.
If TCP is used, the Call Home DOTS server begins by initiating a
TCP connection to the Call Home DOTS client. Once connected, the
Call Home DOTS server continues to initiate a TLS connection to
the Call Home DOTS client.
Peer DOTS agents may have mutual agreement to use a specific port
number, such as by explicit configuration or dynamic discovery
[RFC8973]. The interaction between the base DOTS signal channel
and the Call Home is discussed in Appendix B.
The Happy Eyeballs mechanism explained in Section 4.3 of
[RFC9132] is used for initiating (D)TLS connections.
2. Using this (D)TLS connection, the Call Home DOTS client may
request, withdraw, or retrieve the status of mitigation requests.
The Call Home DOTS client supplies the source information by
means of new attributes defined in Section 5.3.1.
The heartbeat mechanism used for the DOTS Call Home deviates from
the one defined in Section 4.7 of [RFC9132]. Section 5.2.1
specifies the behavior to be followed by Call Home DOTS agents.
5.2. DOTS Signal Channel Variations
5.2.1. Heartbeat Mechanism
Once the (D)TLS section is established between the DOTS agents, the
Call Home DOTS client contacts the Call Home DOTS server to retrieve
the session configuration parameters (Section 4.5 of [RFC9132]). The
Call Home DOTS server adjusts the "heartbeat-interval" to accommodate
binding timers used by on-path NATs and firewalls. Heartbeats will
then be exchanged by the DOTS agents following the instructions
retrieved using the signal channel session configuration exchange.
It is the responsibility of Call Home DOTS servers 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. A Call Home DOTS client MAY trigger their
heartbeat requests immediately after receiving heartbeat probes from
its peer Call Home DOTS server.
When an outgoing attack that saturates the outgoing link from the
Call Home DOTS server is detected and reported by a Call Home DOTS
client, the latter MUST continue to use the DOTS signal channel even
if no traffic is received from the Call Home DOTS server.
If the Call Home DOTS server receives traffic from the Call Home DOTS
client, the Call Home DOTS server MUST continue to use the DOTS
signal channel even if the threshold of allowed missing heartbeats
("missing-hb-allowed") is reached.
If the Call Home DOTS server does not receive any traffic from the
peer Call Home DOTS client during the time span required to exhaust
the maximum "missing-hb-allowed" threshold, the Call Home DOTS server
concludes the session is disconnected. Then, the Call Home DOTS
server MUST try to establish a new DOTS signal channel session,
preferably by resuming the (D)TLS session.
5.2.2. Redirected Signaling
A Call Home DOTS server MUST NOT support the redirected signaling
mechanism as specified in Section 4.6 of [RFC9132] (i.e., a 5.03
response that conveys an alternate DOTS server's Fully Qualified
Domain Name (FQDN) or IP address(es)). A Call Home DOTS client MUST
silently discard such a message as only a Call Home DOTS server can
initiate a new (D)TLS connection.
If a Call Home DOTS client wants to redirect a Call Home DOTS server
to another Call Home DOTS client, it MUST send a Non-confirmable PUT
request to the predefined resource ".well-known/dots/redirect" with
the following attributes in the body of the PUT request:
alt-ch-client: The FQDN of an alternate Call Home DOTS client. It
is also presented as a reference identifier for authentication
purposes.
This is a mandatory attribute for DOTS signal Call Home. It MUST
NOT be used for base DOTS signal channel operations.
alt-ch-client-record: List of IP addresses for the alternate Call
Home DOTS client. If no "alt-ch-client-record" is provided, the
Call Home DOTS server passes the "alt-ch-client" name to a name
resolution library to retrieve one or more IP addresses of the
alternate Call Home DOTS client.
This is an optional attribute for DOTS signal Call Home. It MUST
NOT be used for base DOTS signal channel operations.
ttl: The Time To Live (TTL) of the alternate Call Home DOTS client.
That is, the time interval in which the alternate Call Home DOTS
client may be cached for use by a Call Home DOTS server.
This is an optional attribute for DOTS signal Call Home. It MUST
NOT be used for base DOTS signal channel operations.
On receipt of this PUT request, the Call Home DOTS server responds
with a 2.01 (Created), closes this connection, and establishes a
connection with the new Call Home DOTS client. The processing of the
TTL is defined in Section 4.6 of [RFC9132]. If the Call Home DOTS
server cannot service the PUT request, the response is rejected with
a 4.00 (Bad Request).
Figure 9 shows a PUT request example to convey the alternate Call
Home DOTS client "alt-call-home-client.example" together with its IP
addresses 2001:db8:6401::1 and 2001:db8:6401::2. The validity of
this alternate Call Home DOTS client is 10 minutes.
Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "redirect"
Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw"
Uri-Path: "mid=123"
Content-Format: "application/dots+cbor"
{
"ietf-dots-signal-channel:redirected-signal": {
"ietf-dots-call-home:alt-ch-client":
"alt-call-home-client.example",
"ietf-dots-call-home:alt-ch-client-record": [
"2001:db8:6401::1",
"2001:db8:6401::2"
],
"ietf-dots-call-home:ttl": 600
}
Figure 9: Example of a PUT Request for Redirected Signaling
Figure 9 uses the JSON encoding of YANG-modeled data for the CoAP
message body. The same encoding is used in Figure 10
(Section 5.3.1).
5.3. DOTS Signal Channel Extension
5.3.1. Mitigation Request
This specification extends the mitigation request defined in
Section 4.4.1 of [RFC9132] to convey the attack source information
(e.g., source prefixes, source port numbers). The DOTS client
conveys the following new parameters in the Concise Binary Object
Representation (CBOR) body of the mitigation request:
source-prefix: A list of attacker IP prefixes used to attack the
target. Prefixes are represented using Classless Inter-Domain
Routing (CIDR) notation (BCP 122 [RFC4632]).
As a reminder, the prefix length MUST be less than or equal to 32
(or 128) for IPv4 (or IPv6).
The prefix list MUST NOT include broadcast, loopback, or multicast
addresses. These addresses are considered invalid values. Note
that link-local addresses are allowed. The Call Home DOTS client
MUST validate that attacker prefixes are within the scope of the
Call Home DOTS server domain (e.g., prefixes assigned to the Call
Home DOTS server domain or networks it services). This check is
meant to avoid contacting Call Home DOTS servers that are not
entitled to enforce actions on specific prefixes.
This is an optional attribute for the base DOTS signal channel
operations.
source-port-range: A list of port numbers used by the attack traffic
flows.
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 any subrange of 0-65535 -- for
example, 0-1023, 1024-65535, or 1024-49151.
This is an optional attribute for the base DOTS signal channel
operations.
source-icmp-type-range: A list of ICMP types used by the attack
traffic flows. An ICMP type range is defined by two bounds, a
lower ICMP type (lower-type) and an upper ICMP type (upper-type).
When only "lower-type" is present, it represents a single ICMP
type. Both ICMP [RFC0792] and ICMPv6 [RFC4443] types are
supported. Whether ICMP or ICMPv6 types are to be used is
determined by the address family of the "target-prefix".
This is an optional attribute for the base DOTS signal channel
operations.
The "source-prefix" parameter is a mandatory attribute when the
attack traffic information is signaled by a Call Home DOTS client
(i.e., the Call Home scenario depicted in Figure 8). The "target-
prefix" attribute MUST be included in the mitigation request
signaling the attack information to a Call Home DOTS server. The
"target-uri" or "target-fqdn" parameters can be included in a
mitigation request for diagnostic purposes to notify the Call Home
DOTS server domain administrator but SHOULD NOT be used to determine
the target IP addresses. "alias-name" is unlikely to be conveyed in
a Call Home mitigation request given that a target may be any IP
resource and that there is no incentive for a Call Home DOTS server
(embedded, for example, in a CPE) to maintain aliases.
In order to help attack source identification by a Call Home DOTS
server, the Call Home DOTS client SHOULD include in its mitigation
request additional information such as "source-port-range" or
"source-icmp-type-range" to disambiguate nodes sharing the same
"source-prefix". IPv6 addresses/prefixes are sufficient to uniquely
identify a network endpoint, without need for port numbers or ICMP
type information. While this is also possible for IPv4, it is much
less often the case than for IPv6. More address sharing implications
on the setting of source information ("source-prefix", "source-port-
range") are discussed in Section 5.3.2.
Only immediate mitigation requests (i.e., "trigger-mitigation" set to
"true") are allowed; Call Home DOTS clients MUST NOT send requests
with "trigger-mitigation" set to "false". Such requests MUST be
discarded by the Call Home DOTS server with a 4.00 (Bad Request).
An example of a mitigation request sent by a Call Home DOTS client is
shown in Figure 10.
Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw"
Uri-Path: "mid=56"
Content-Format: "application/dots+cbor"
{
"ietf-dots-signal-channel:mitigation-scope": {
"scope": [
{
"target-prefix": [
"2001:db8:c000::/128"
],
"ietf-dots-call-home:source-prefix": [
"2001:db8:123::1/128"
],
"lifetime": 3600
}
]
}
}
Figure 10: An Example of a Mitigation Request Issued by a Call
Home DOTS Client
The Call Home DOTS server MUST check that the "source-prefix" is
within the scope of the Call Home DOTS server domain. Note that in a
DOTS Call Home scenario, the Call Home DOTS server considers, by
default, that any routable IP prefix enclosed in "target-prefix" is
within the scope of the Call Home DOTS client. Invalid mitigation
requests are handled as per Section 4.4.1 of [RFC9132].
Note: These validation checks do not apply when the source
information is included as a hint in the context of the base DOTS
signal channel.
Call Home DOTS server domain administrator consent MAY be required to
block the traffic from the compromised device to the attack target.
An implementation MAY have a configuration knob to block the traffic
from the compromised device to the attack target with or without DOTS
server domain administrator consent.
If consent from the Call Home DOTS server domain administrator is
required, the Call Home DOTS server replies with 2.01 (Created) and
the "status" code set to 1 (attack-mitigation-in-progress). Then,
the mechanisms defined in Section 4.4.2 of [RFC9132] are followed by
the DOTS agents to update the mitigation status. In particular, if
the attack traffic is blocked, the Call Home DOTS server informs the
Call Home DOTS client that the attack is being mitigated (i.e., by
setting the "status" code to 2 (attack-successfully-mitigated)).
If the attack traffic information is identified by the Call Home DOTS
server or the Call Home DOTS server domain administrator as
legitimate traffic, the mitigation request is rejected with a 4.09
(Conflict) (e.g., when no consent is required from an administrator)
or a notification message with the "conflict-clause" (Section 4.4.1
of [RFC9132]) set to the following new value:
4: Mitigation request rejected. This code is returned by the DOTS
server to indicate the attack traffic has been classified as
legitimate traffic.
Once the request is validated by the Call Home DOTS server,
appropriate actions are enforced to block the attack traffic within
the source network. For example, if the Call Home DOTS server is
embedded in a CPE, it can program the packet processor to punt all
the traffic from the compromised device to the target to slow path.
The CPE inspects the punted slow path traffic to detect and block the
outgoing DDoS attack traffic or quarantine the device (e.g., using
MAC-level filtering) until it is remediated and notifies the CPE
administrator about the compromised device. Note that the Call Home
DOTS client is informed about the progress of the attack mitigation
following the rules in Section 4.4.2 of [RFC9132].
The DOTS agents follow the same procedures specified in [RFC9132] for
managing a mitigation request.
5.3.2. Address Sharing Considerations
Figure 11 depicts an example of a network provider that hosts a Call
Home DOTS client and deploys a Carrier-Grade NAT (CGN) between the
DOTS client domain and DOTS server domain. In such cases,
communicating an external IP address in a mitigation request by a
Call Home DOTS client is likely to be discarded by the Call Home DOTS
server because the external IP address is not visible locally to the
Call Home DOTS server (Figure 11). The Call Home DOTS server is only
aware of the internal IP addresses/prefixes bound to its domain
(i.e., those used in the internal realm shown in Figure 11). Thus,
Call Home DOTS clients that are aware of the presence of on-path CGNs
MUST NOT include the external IP address and/or port number
identifying the suspect attack source (i.e., those used in the
external realm shown in Figure 11) but MUST include the internal IP
address and/or port number. To that aim, the Call Home DOTS client
SHOULD rely on mechanisms, such as those described in [RFC8512] or
[RFC8513], to retrieve the internal IP address and port number that
are mapped to an external IP address and port number. For the
particular case of NAT64 [RFC6146], if the target address is an IPv4
address, the IPv4-converted IPv6 address of this target address
[RFC6052] SHOULD be used.
N | .-------------------.
E | ( )-.
T | .' '
W | ( Call Home )
O | ( DOTS client -'
R | '-( )
K | '-------+-----------'
| |
P | |
R | +---+---+
O | | CGN | External Realm
V |..............| |......................
I | | | Internal Realm
D | +---+---+
E | |
R | |
--- |
.---------+---------.
( )-.
.' Source Network '
( )
( Call Home -'
'-( DOTS server )
'------+------------'
|
+-----+-------+
|Attack Source|
+-------------+
Figure 11: Example of a CGN between DOTS Domains
If a Mapping of Address and Port (MAP) Border Relay [RFC7597] or
Lightweight Address Family Transition Router (lwAFTR) [RFC7596] is
enabled in the provider's domain to service its customers, the
identification of an attack source bound to an IPv4 address/prefix
MUST also rely on source port numbers because the same IPv4 address
is assigned to multiple customers. The port information is required
to unambiguously identify the source of an attack.
If a translator is enabled on the boundaries of the domain hosting
the Call Home DOTS server (e.g., a CPE with NAT enabled as shown in
Figures 12 and 13), the Call Home DOTS server uses the attack traffic
information conveyed in a mitigation request to find the internal
source IP address of the compromised device and blocks the traffic
from the compromised device traffic to the attack target until the
mitigation request is withdrawn. The Call Home DOTS server proceeds
with a NAT mapping table lookup using the attack information (or a
subset thereof) as a key. The lookup can be local (Figure 12) or via
a dedicated administration interface that is offered by the CPE
(Figure 13). This identification allows the suspicious device to be
isolated while avoiding disturbances of other services.
.-------------------.
( )-.
.' Network Provider (DMS)'
( )
( Call Home -'
'-( DOTS client )
'-------+-----------'
|
--- +---+---+
S | | CPE | External Realm
O |..............| |................
U | | NAT | Internal Realm
R | +---+---+
C | |
E | .---------+---------.
| ( )-.
N | .' '
E | ( Call Home )
T | ( DOTS server -'
W | '-( )
O | '-------+-----------'
R | |
K | +------+------+
| |Attack Source|
+-------------+
Figure 12: Example of a DOTS Server Domain with a NAT Embedded in
a CPE
.-------------------.
( )-.
.' Network Provider (DMS) '
( )
( Call Home -'
'-( DOTS client )
'---------+---------'
|
--- +-----+-----+
S | | CPE/NAT | External Realm
O |..............| |................
U | | Call Home | Internal Realm
R | |DOTS server|
C | +-----+-----+
E | |
| .-----------+-------.
| ( )-.
N | .' '
E | ( Local Area Network )
T | ( -'
W | '-( )
O | '--------+----------'
R | |
K | +------+------+
| |Attack Source|
+-------------+
Figure 13: Example of a Call Home DOTS Server and a NAT Embedded
in a CPE
If, for any reason, address sharing is deployed in both source and
provider networks, both Call Home DOTS agents have to proceed with
address mapping lookups following the behavior specified in reference
to Figure 11 (network provider) and Figures 12 and 13 (source
network).
6. DOTS Signal Call Home YANG Module
6.1. Tree Structure
This document augments the "ietf-dots-signal-channel" (dots-signal)
DOTS signal YANG module defined in [RFC9132] for signaling the attack
traffic information. This document defines the YANG module "ietf-
dots-call-home", which has the following tree structure:
module: ietf-dots-call-home
augment-structure /dots-signal:dots-signal/dots-signal:message-type
/dots-signal:mitigation-scope/dots-signal:scope:
+-- source-prefix* inet:ip-prefix
+-- source-port-range* [lower-port]
| +-- lower-port inet:port-number
| +-- upper-port? inet:port-number
+-- source-icmp-type-range* [lower-type]
+-- lower-type uint8
+-- upper-type? uint8
augment-structure /dots-signal:dots-signal/dots-signal:message-type
/dots-signal:redirected-signal:
+-- (type)?
+--:(call-home-only)
+-- alt-ch-client inet:domain-name
+-- alt-ch-client-record* inet:ip-address
+-- ttl? uint32
6.2. YANG/JSON Mapping Parameters to CBOR
The YANG/JSON mapping parameters to CBOR are listed in Table 1.
Note: Implementers must check that the mapping output provided by
their YANG-to-CBOR encoding schemes is aligned with the content of
Table 1.
+========================+=============+=====+=============+========+
|Parameter Name |YANG Type |CBOR |CBOR Major | JSON |
| | |Key |Type & | Type |
| | |Value|Information | |
+========================+=============+=====+=============+========+
|ietf-dots-call- |leaf-list |32768|4 array | Array |
|home:source-prefix |inet:ip- | |3 text string| String |
| |prefix | | | |
+------------------------+-------------+-----+-------------+--------+
|ietf-dots-call- |list |32769|4 array | Array |
|home:source-port-range | | | | |
+------------------------+-------------+-----+-------------+--------+
|ietf-dots-call- |list |32770|4 array | Array |
|home:source-icmp-type- | | | | |
|range | | | | |
+------------------------+-------------+-----+-------------+--------+
|lower-type |uint8 |32771|0 unsigned | Number |
+------------------------+-------------+-----+-------------+--------+
|upper-type |uint8 |32772|0 unsigned | Number |
+------------------------+-------------+-----+-------------+--------+
|ietf-dots-call-home:alt-|inet: domain-|32773|3 text string| String |
|ch-client |name | | | |
+------------------------+-------------+-----+-------------+--------+
|ietf-dots-call-home:alt-|leaf-list |32774|4 array | Array |
|ch-client-record |inet:ip- | |3 text string| String |
| |address | | | |
+------------------------+-------------+-----+-------------+--------+
|ietf-dots-call-home:ttl |uint32 |32775|0 unsigned | Number |
+------------------------+-------------+-----+-------------+--------+
Table 1: YANG/JSON Mapping Parameters to CBOR
The YANG/JSON mappings to CBOR for "lower-port" and "upper-port" are
already defined in Table 5 of [RFC9132].
6.3. YANG Module
This module uses the common YANG types defined in [RFC6991] and the
data structure extension defined in [RFC8791].
<CODE BEGINS> file "ietf-dots-call-home@2021-12-09.yang"
module ietf-dots-call-home {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-dots-call-home";
prefix dots-call-home;
import ietf-inet-types {
prefix inet;
reference
"Section 4 of RFC 6991";
}
import ietf-dots-signal-channel {
prefix dots-signal;
reference
"RFC 9132: 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>
Author: Konda, Tirumaleswar Reddy
<mailto:kondtir@gmail.com>;
Author: Mohamed Boucadair
<mailto:mohamed.boucadair@orange.com>;
Author: Jon Shallow
<mailto:ietf-supjps@jpshallow.com>";
description
"This module contains YANG definitions for the signaling
messages exchanged between a DOTS client and a DOTS server
for the Call Home deployment scenario.
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 9066; see
the RFC itself for full legal notices.";
revision 2021-12-09 {
description
"Initial revision.";
reference
"RFC 9066: Distributed Denial-of-Service Open Threat
Signaling (DOTS) Signal Channel Call Home";
}
sx:augment-structure "/dots-signal:dots-signal"
+ "/dots-signal:message-type"
+ "/dots-signal:mitigation-scope"
+ "/dots-signal:scope" {
description
"Attack source details.";
leaf-list source-prefix {
type inet:ip-prefix;
description
"IPv4 or IPv6 prefix identifying the attack source(s).";
}
list source-port-range {
key "lower-port";
description
"Port range. When only lower-port is
present, it represents a single port number.";
leaf lower-port {
type inet:port-number;
description
"Lower port number of the port range.";
}
leaf upper-port {
type inet:port-number;
must '. >= ../lower-port' {
error-message
"The upper port number must be greater than
or equal to the lower port number.";
}
description
"Upper port number of the port range.";
}
}
list source-icmp-type-range {
key "lower-type";
description
"ICMP/ICMPv6 type range. When only lower-type is
present, it represents a single ICMP/ICMPv6 type.
The address family of the target-prefix is used
to determine whether ICMP or ICMPv6 is used.";
leaf lower-type {
type uint8;
description
"Lower ICMP/ICMPv6 type of the ICMP type range.";
reference
"RFC 792: Internet Control Message Protocol
RFC 4443: Internet Control Message Protocol (ICMPv6)
for the Internet Protocol Version 6 (IPv6)
Specification.";
}
leaf upper-type {
type uint8;
must '. >= ../lower-type' {
error-message
"The upper ICMP/ICMPv6 type must be greater than
or equal to the lower ICMP type.";
}
description
"Upper type of the ICMP type range.";
reference
"RFC 792: Internet Control Message Protocol
RFC 4443: Internet Control Message Protocol (ICMPv6)
for the Internet Protocol Version 6 (IPv6)
Specification.";
}
}
}
sx:augment-structure "/dots-signal:dots-signal"
+ "/dots-signal:message-type"
+ "/dots-signal:redirected-signal" {
description
"Augments the redirected signal to communicate an
alternate Call Home DOTS client.";
choice type {
description
"Indicates the type of the DOTS session (e.g., base
DOTS signal channel, DOTS Call Home).";
case call-home-only {
description
"These attributes appear only in a signal Call Home
channel message from a Call Home DOTS client
to a Call Home DOTS server.";
leaf alt-ch-client {
type inet:domain-name;
mandatory true;
description
"FQDN of an alternate Call Home DOTS client.
This name is also presented as a reference
identifier for authentication purposes.";
}
leaf-list alt-ch-client-record {
type inet:ip-address;
description
"List of IP addresses for the alternate Call
Home DOTS client.
If this data node is not present, a Call Home
DOTS server resolves the alt-ch-client into
one or more IP addresses.";
}
leaf ttl {
type uint32;
units "seconds";
description
"The Time To Live (TTL) of the alternate Call Home
DOTS client.";
reference
"Section 4.6 of RFC 9132";
}
}
}
}
}
<CODE ENDS>
7. IANA Considerations
7.1. DOTS Signal Channel CBOR Mappings Registry
This specification registers the following comprehension-optional
parameters (Table 2) in the IANA "DOTS Signal Channel CBOR Key
Values" registry [Key-Map].
+========================+=======+=======+============+===========+
| Parameter Name | CBOR | CBOR | Change | Reference |
| | Key | Major | Controller | |
| | Value | Type | | |
+========================+=======+=======+============+===========+
| ietf-dots-call- | 32768 | 4 | IESG | RFC 9066 |
| home:source-prefix | | | | |
+------------------------+-------+-------+------------+-----------+
| ietf-dots-call- | 32769 | 4 | IESG | RFC 9066 |
| home:source-port-range | | | | |
+------------------------+-------+-------+------------+-----------+
| ietf-dots-call- | 32770 | 4 | IESG | RFC 9066 |
| home:source-icmp-type- | | | | |
| range | | | | |
+------------------------+-------+-------+------------+-----------+
| lower-type | 32771 | 0 | IESG | RFC 9066 |
+------------------------+-------+-------+------------+-----------+
| upper-type | 32772 | 0 | IESG | RFC 9066 |
+------------------------+-------+-------+------------+-----------+
| ietf-dots-call- | 32773 | 3 | IESG | RFC 9066 |
| home:alt-ch-client | | | | |
+------------------------+-------+-------+------------+-----------+
| ietf-dots-call- | 32774 | 4 | IESG | RFC 9066 |
| home:alt-ch-client- | | | | |
| record | | | | |
+------------------------+-------+-------+------------+-----------+
| ietf-dots-call-home: | 32775 | 0 | IESG | RFC 9066 |
| ttl | | | | |
+------------------------+-------+-------+------------+-----------+
Table 2: Assigned DOTS Signal Channel CBOR Key Values
7.2. New DOTS Conflict Cause
Per this document, IANA has assigned a new code from the "DOTS Signal
Channel Conflict Cause Codes" registry [Cause].
+====+=====================================+=============+==========+
|Code| Label |Description |Reference |
+====+=====================================+=============+==========+
|4 | request-rejected-legitimate-traffic |Mitigation |RFC 9066 |
| | |request | |
| | |rejected. | |
| | |This code is | |
| | |returned by | |
| | |the DOTS | |
| | |server to | |
| | |indicate the | |
| | |attack | |
| | |traffic has | |
| | |been | |
| | |classified as| |
| | |legitimate | |
| | |traffic. | |
+----+-------------------------------------+-------------+----------+
Table 3: Assigned DOTS Signal Channel Conflict Cause Code
7.3. DOTS Signal Call Home YANG Module
Per this document, IANA has registered the following URI in the "ns"
subregistry within the "IETF XML Registry" [RFC3688]:
URI: urn:ietf:params:xml:ns:yang:ietf-dots-call-home
Registrant Contact: The IETF.
XML: N/A; the requested URI is an XML namespace.
Per this document, IANA has registered the following YANG module in
the "YANG Module Names" subregistry [RFC6020] within the "YANG
Parameters" registry:
name: ietf-dots-call-home
namespace: urn:ietf:params:xml:ns:yang:ietf-dots-call-home
maintained by IANA: N
prefix: dots-call-home
reference: RFC 9066
8. Security Considerations
This document deviates from classic DOTS signal channel usage by
having the DOTS server initiate the (D)TLS connection. Security
considerations related to the DOTS signal channel discussed in
Section 11 of [RFC9132] and (D)TLS early data discussed in Section 7
of [RFC9132] MUST be considered. DOTS agents MUST authenticate each
other using (D)TLS before a DOTS signal channel session is considered
valid.
The Call Home function enables a Call Home DOTS server to be
reachable by only the intended Call Home DOTS client. Appropriate
filters (e.g., access control lists) can be installed on the Call
Home DOTS server and network between the Call Home DOTS agents so
that only communications from a trusted Call Home DOTS client to the
Call Home DOTS server are allowed. These filters can be
automatically installed by a Call Home DOTS server based on the
configured or discovered peer Call Home DOTS client(s).
An attacker may launch a DoS attack on the DOTS client by having it
perform computationally expensive operations before deducing that the
attacker doesn't possess a valid key. For instance, in TLS 1.3
[RFC8446], the ServerHello message contains a key share value based
on an expensive asymmetric key operation for key establishment.
Common precautions mitigating DoS attacks are recommended, such as
temporarily adding the source address to a drop-list after a set
number of unsuccessful authentication attempts.
The DOTS signal Call Home channel can be misused by a misbehaving
Call Home DOTS client by arbitrarily signaling legitimate traffic as
being attack traffic or falsifying mitigation signals so that some
sources are disconnected or some traffic is rate-limited. Such
misbehaving Call Home DOTS clients may include sources identified by
IP addresses that are used for internal use only (that is, these
addresses are not visible outside a Call Home DOTS server domain).
Absent explicit policy (e.g., the Call Home DOTS client and server
are managed by the same administrative entity), such requests should
be discarded by the Call Home DOTS server. More generally, Call Home
DOTS servers should not blindly trust mitigation requests from Call
Home DOTS clients. For example, Call Home DOTS servers could use the
attack flow information contained in a mitigation request to enable a
full-fledged packet inspection function to inspect all the traffic
from the compromised device to the target. They could also redirect
the traffic from the potentially compromised device to the target
towards a DDoS mitigation system that can scrub the suspicious
traffic without blindly blocking all traffic from the indicated
attack source to the target. Call Home DOTS servers can also seek
the consent of the DOTS server domain administrator to block the
traffic from the potentially compromised device to the target (see
Section 5.3.1). The means to seek consent are implementation
specific.
Call Home DOTS agents may interact with on-path address sharing
functions to retrieve an internal IP address / external IP address
mapping (Section 5.3.2) identifying an attack source. Blocking
access or manipulating the mapping information will complicate DDoS
attack mitigation close to an attack source. Additional security
considerations are specific to the actual mechanism used to access
that mapping (refer, e.g., to Section 4 of [RFC8512] or Section 4 of
[RFC8513]).
This document augments YANG data structures that are meant to be used
as an abstract representation of DOTS signal channel Call Home
messages. As such, the "ietf-dots-call-home" module does not
introduce any new vulnerabilities beyond those specified above and in
[RFC9132].
9. Privacy Considerations
The considerations discussed in [RFC6973] were taken into account to
assess whether the DOTS Call Home introduces privacy threats.
Concretely, the protocol does not leak any new information that can
be used to ease surveillance. In particular, the Call Home DOTS
server is not required to share information that is local to its
network (e.g., internal identifiers of an attack source) with the
Call Home DOTS client. Also, the recommended data to be included in
Call Home DOTS messages is a subset of the Layer 3 / Layer 4
information that can be learned from the overall traffic flows that
exit the Call Home DOTS server domain. Furthermore, Call Home DOTS
clients do not publicly reveal attack identification information;
that information is encrypted and only shared with an authorized
entity in the domain to which the IP address/prefix is assigned, from
which an attack was issued.
The DOTS Call Home does not preclude the validation of mitigation
requests received from a Call Home DOTS client. For example, a
security service running on the CPE may require an administrator's
consent before the CPE acts upon the mitigation request indicated by
the Call Home DOTS client. How the consent is obtained is out of
scope of this document.
Note that a Call Home DOTS server can seek an administrator's
consent, validate the request by inspecting the relevant traffic for
attack signatures, or proceed with both courses of action.
The DOTS Call Home is only advisory in nature. Concretely, the DOTS
Call Home does not impose any action to be enforced within the
network hosting an attack source; it is up to the Call Home DOTS
server (and/or network administrator) to decide whether and which
actions are required.
Moreover, the DOTS Call Home avoids misattribution by appropriately
identifying the network to which a suspect attack source belongs
(e.g., address sharing issues discussed in Section 5.3.1).
Triggers to send a DOTS mitigation request to a Call Home DOTS server
are deployment specific. For example, a Call Home DOTS client may
rely on the output of some DDoS detection systems (flow exports or
similar functions) deployed within the DOTS client domain to detect
potential outbound DDoS attacks or may rely on abuse claims received
from remote victim networks. These systems may be misused to track
users and infer their activities. Such misuses are not required to
achieve the functionality defined in this document (that is, protect
the Internet and avoid altering the IP reputation of source
networks). It is out of the scope to identify privacy threats
specific to given attack detection technology. The reader may refer,
for example, to Section 11.8 of [RFC7011].
10. References
10.1. Normative References
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<https://www.rfc-editor.org/info/rfc792>.
[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>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[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>.
[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>.
[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>.
[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>.
[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>.
[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>.
[RFC8791] Bierman, A., Björklund, M., and K. Watsen, "YANG Data
Structure Extensions", RFC 8791, DOI 10.17487/RFC8791,
June 2020, <https://www.rfc-editor.org/info/rfc8791>.
[RFC9132] Boucadair, M., Ed., Shallow, J., and T. Reddy.K,
"Distributed Denial-of-Service Open Threat Signaling
(DOTS) Signal Channel Specification", RFC 9132,
DOI 10.17487/RFC9132, September 2021,
<https://www.rfc-editor.org/info/rfc9132>.
10.2. Informative References
[Cause] IANA, "DOTS Signal Channel Conflict Cause Codes",
<https://www.iana.org/assignments/dots/>.
[DOTS-MULTIHOMING]
Boucadair, M., Reddy, T., and W. Pan, "Multi-homing
Deployment Considerations for Distributed-Denial-of-
Service Open Threat Signaling (DOTS)", Work in Progress,
Internet-Draft, draft-ietf-dots-multihoming-09, 2 December
2021, <https://datatracker.ietf.org/doc/html/draft-ietf-
dots-multihoming-09>.
[DTLS13] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", Work in Progress, Internet-Draft, draft-ietf-tls-
dtls13-43, 30 April 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
dtls13-43>.
[I2NSF-TERMS]
Hares, S., Strassner, J., Lopez, D. R., Xia, L., and H.
Birkholz, "Interface to Network Security Functions (I2NSF)
Terminology", Work in Progress, Internet-Draft, draft-
ietf-i2nsf-terminology-08, 5 July 2019,
<https://datatracker.ietf.org/doc/html/draft-ietf-i2nsf-
terminology-08>.
[Key-Map] IANA, "DOTS Signal Channel CBOR Key Values",
<https://www.iana.org/assignments/dots/>.
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations",
RFC 2663, DOI 10.17487/RFC2663, August 1999,
<https://www.rfc-editor.org/info/rfc2663>.
[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>.
[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>.
[RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet
Denial-of-Service Considerations", RFC 4732,
DOI 10.17487/RFC4732, December 2006,
<https://www.rfc-editor.org/info/rfc4732>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>.
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<https://www.rfc-editor.org/info/rfc4960>.
[RFC6398] Le Faucheur, F., Ed., "IP Router Alert Considerations and
Usage", BCP 168, RFC 6398, DOI 10.17487/RFC6398, October
2011, <https://www.rfc-editor.org/info/rfc6398>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>.
[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, DOI 10.17487/RFC7011, September 2013,
<https://www.rfc-editor.org/info/rfc7011>.
[RFC7596] Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I.
Farrer, "Lightweight 4over6: An Extension to the Dual-
Stack Lite Architecture", RFC 7596, DOI 10.17487/RFC7596,
July 2015, <https://www.rfc-editor.org/info/rfc7596>.
[RFC7597] Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S.,
Murakami, T., and T. Taylor, Ed., "Mapping of Address and
Port with Encapsulation (MAP-E)", RFC 7597,
DOI 10.17487/RFC7597, July 2015,
<https://www.rfc-editor.org/info/rfc7597>.
[RFC8071] Watsen, K., "NETCONF Call Home and RESTCONF Call Home",
RFC 8071, DOI 10.17487/RFC8071, February 2017,
<https://www.rfc-editor.org/info/rfc8071>.
[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>.
[RFC8512] Boucadair, M., Ed., Sivakumar, S., Jacquenet, C.,
Vinapamula, S., and Q. Wu, "A YANG Module for Network
Address Translation (NAT) and Network Prefix Translation
(NPT)", RFC 8512, DOI 10.17487/RFC8512, January 2019,
<https://www.rfc-editor.org/info/rfc8512>.
[RFC8513] Boucadair, M., Jacquenet, C., and S. Sivakumar, "A YANG
Data Model for Dual-Stack Lite (DS-Lite)", RFC 8513,
DOI 10.17487/RFC8513, January 2019,
<https://www.rfc-editor.org/info/rfc8513>.
[RFC8517] Dolson, D., Ed., Snellman, J., Boucadair, M., Ed., and C.
Jacquenet, "An Inventory of Transport-Centric Functions
Provided by Middleboxes: An Operator Perspective",
RFC 8517, DOI 10.17487/RFC8517, February 2019,
<https://www.rfc-editor.org/info/rfc8517>.
[RFC8576] Garcia-Morchon, O., Kumar, S., and M. Sethi, "Internet of
Things (IoT) Security: State of the Art and Challenges",
RFC 8576, DOI 10.17487/RFC8576, April 2019,
<https://www.rfc-editor.org/info/rfc8576>.
[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>.
[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>.
[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>.
[RFC8955] Loibl, C., Hares, S., Raszuk, R., McPherson, D., and M.
Bacher, "Dissemination of Flow Specification Rules",
RFC 8955, DOI 10.17487/RFC8955, December 2020,
<https://www.rfc-editor.org/info/rfc8955>.
[RFC8956] Loibl, C., Ed., Raszuk, R., Ed., and S. Hares, Ed.,
"Dissemination of Flow Specification Rules for IPv6",
RFC 8956, DOI 10.17487/RFC8956, December 2020,
<https://www.rfc-editor.org/info/rfc8956>.
[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>.
[RS] RSnake, "Slowloris HTTP DoS",
<https://web.archive.org/web/20150315054838/
http://ha.ckers.org/slowloris/>.
[Sec-by-design]
UK Department for Digital, Culture, Media & Sport, "Secure
by Design: Improving the cyber security of consumer
Internet of Things Report", March 2018,
<https://www.gov.uk/government/publications/secure-by-
design-report>.
Appendix A. Some Home Network Issues
Internet of Things (IoT) devices are becoming more and more
prevalent, in particular in home networks. With compute and memory
becoming cheaper and cheaper, various types of IoT devices become
available in the consumer market at affordable prices. But on the
downside, there is a corresponding threat since most of these IoT
devices are bought off-the-shelf and most manufacturers haven't
considered security in the product design (e.g., [Sec-by-design]).
IoT devices deployed in home networks can be easily compromised, they
often do not have an easy mechanism to upgrade, and even when
upgradable, IoT manufacturers may cease manufacture and/or
discontinue patching vulnerabilities on IoT devices (Sections 5.4 and
5.5 of [RFC8576]). These vulnerable and compromised devices will
continue to be used for a long period of time in the home, and the
end-user does not know that IoT devices in his/her home are
compromised. The compromised IoT devices are typically used for
launching DDoS attacks (Section 3 of [RFC8576]) on victims while the
owner/administrator of the home network is not aware about such
misbehaviors. Similar to other DDoS attacks, the victim in this
attack can be an application server, a host, a router, a firewall, or
an entire network. Such misbehaviors can cause collateral damage
that will affect end users, and can also harm the reputation of an
Internet Service Provider (ISP) for being a source of attack traffic.
Nowadays, network devices in a home network can offer network
security functions (e.g., firewall [RFC4949] or Intrusion Protection
System (IPS) service [I2NSF-TERMS] on a home router) to protect the
devices connected to the home network from both external and internal
attacks. It is natural to seek to provide DDoS defense in these
devices as well, and over the years several techniques have been
identified to detect DDoS attacks; some of these techniques can be
enabled on home network devices but most of them are used within the
ISP's network.
Some of the DDoS attacks like spoofed RST or FIN packets, Slowloris
[RS], and Transport Layer Security (TLS) renegotiation are difficult
to detect on a home network device without adversely affecting its
performance. The reason is that typically home devices such as home
routers have fast path to boost the throughput. For every new TCP/
UDP flow, only the first few packets are punted through the slow
path. Hence, it is not possible to detect various DDoS attacks in
the slow path, since the attack payload is sent to the target server
after the flow is switched to fast path. The reader may refer to
Section 2 of [RFC6398] for a brief definition of slow and fast paths.
Deep Packet Inspection (DPI) of all the packets of a flow would be
able to detect some of the attacks. However, a full-fledged DPI to
detect these type of DDoS attacks is functionally or operationally
not possible for all the devices attached to the home network because
of the memory and CPU limitations of the home routers. Furthermore,
for certain DDoS attacks the logic needed to distinguish legitimate
traffic from attack traffic on a per-packet basis is complex. This
complexity is because that the packet itself may look "legitimate"
and no attack signature can be identified. The anomaly can be
identified only after detailed statistical analysis. In addition,
network security services in home networks may not be able to detect
all types of DDoS attacks using DPI. ISPs offering DDoS mitigation
services have a DDoS detection capability that relies upon anomaly
detection to identify zero day DDoS attacks and to detect DDoS
attacks that cannot be detected using signatures and rate-limit
techniques.
ISPs can detect some DDoS attacks originating from a home network
(e.g., Section 2.6 of [RFC8517]), but the ISP usually does not have a
mechanism to detect which device in the home network is generating
the DDoS attack traffic. The primary reason for this is that devices
in an IPv4 home network are typically behind a Network Address
Translation (NAT) border [RFC2663]. Even in case of an IPv6 home
network, although the ISP can identify the infected device in the
home network launching the DDoS traffic by tracking its unique IPv6
address, the infected device can easily change its IPv6 address to
evade remediation. A security function on the local home network is
better positioned to track the compromised device across IPv6 address
(and potentially even MAC address) changes and thus ensure that
remediation remains in place across such events.
Appendix B. Disambiguating Base DOTS Signal vs. DOTS Call Home
With the DOTS signal channel Call Home, there is a chance that two
DOTS agents can simultaneously establish two DOTS signal channels
with different directions (base DOTS signal channel and DOTS signal
channel Call Home). Here is one example drawn from the home network.
Nevertheless, the outcome of the discussion is not specific to these
networks, but applies to any DOTS Call Home scenario.
In the Call Home scenario, the Call Home DOTS server in, for example,
the home network can mitigate the DDoS attacks launched by the
compromised device in its domain by receiving the mitigation request
sent by the Call Home DOTS client in the ISP environment. In
addition, the DOTS client in the home network can initiate a
mitigation request to the DOTS server in the ISP environment to ask
for help when the home network is under a DDoS attack. Such Call
Home DOTS server and DOTS client in the home network can co-locate in
the same home network element (e.g., the Customer Premises
Equipment). In this case, with the same peer at the same time the
home network element will have the base DOTS signal channel defined
in [RFC9132] and the DOTS signal channel Call Home defined in this
specification. Thus, these two signal channels need to be
distinguished when they are both supported. Two approaches have been
considered for distinguishing the two DOTS signal channels, but only
the one that using the dedicated port number has been chosen as the
best choice.
By using a dedicated port number for each, these two signal channels
can be separated unambiguously and easily. For example, the CPE uses
the port number 4646 allocated in [RFC9132] to initiate the basic
signal channel to the ISP when it acts as the DOTS client, and uses
another port number to initiate the signal channel Call Home. Based
on the different port numbers, the ISP can directly decide which kind
of procedures should follow immediately after it receives the DOTS
messages. This approach just requires two (D)TLS sessions to be
established respectively for the basic signal channel and signal
channel Call Home.
The other approach is signaling the role of each DOTS agent (e.g., by
using the DOTS data channel as depicted in Figure 14). For example,
the DOTS agent in the home network first initiates a DOTS data
channel to the peer DOTS agent in the ISP environment, at this time
the DOTS agent in the home network is the DOTS client and the peer
DOTS agent in the ISP environment is the DOTS server. After that,
the DOTS agent in the home network retrieves the DOTS Call Home
capability of the peer DOTS agent. If the peer supports the DOTS
Call Home, the DOTS agent needs to subscribe to the peer to use this
extension. Then, the reversal of DOTS role can be recognized as done
by both DOTS agents. When the DOTS agent in the ISP environment,
which now is the DOTS client, wants to filter the attackers' traffic,
it requests the DOTS agent in the home network, which now is the DOTS
server, for help.
augment /ietf-data:dots-data/ietf-data:capabilities:
+--ro call-home-support? boolean
augment /ietf-data:dots-data/ietf-data:dots-client:
+--rw call-home-enable? boolean
Figure 14: Example of DOTS Data Channel Augmentation
Signaling the role will complicate the DOTS protocols, and this
complexity is not required in context where the DOTS Call Home is not
required or only when the DOTS Call Home is needed. Besides, the
DOTS data channel may not work during attack time. Even if changing
the above example from using the DOTS data channel to the DOTS signal
channel, the more procedures will still reduce the efficiency. Using
the dedicated port number is much easier and more concise compared to
the second approach, and its cost that establishing two (D)TLS
sessions is much less. So, using a dedicated port number for the
DOTS Call Home is recommended in this specification. The dedicated
port number can be configured locally or discovered using means such
as [RFC8973].
Acknowledgements
Thanks to Wei Pei, Xia Liang, Roman Danyliw, Dan Wing, Toema
Gavrichenkov, Daniel Migault, Sean Turner, and Valery Smyslov for the
comments.
Benjamin Kaduk's AD review is valuable. Many thanks to him for the
detailed review.
Thanks to Radia Perlman and David Schinazi for the directorate
reviews.
Thanks to Ebben Aries for the YANG Doctors review.
Thanks to Éric Vyncke, Roman Danyliw, Barry Leiba, Robert Wilton, and
Erik Kline for the IESG review.
Contributors
The following individuals have contributed to this document:
Joshi Harsha
McAfee, Inc.
Embassy Golf Link Business Park
Bangalore 560071
Karnataka
India
Email: harsha_joshi@mcafee.com
Wei Pan
Huawei Technologies
China
Email: william.panwei@huawei.com
Authors' Addresses
Tirumaleswar Reddy.K
Akamai
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
Jon Shallow
United Kingdom
Email: supjps-ietf@jpshallow.com