Distributed Denial-of-Service
Open Threat Signaling (DOTS) Signal Channel SpecificationMcAfee, Inc.Embassy Golf Link Business ParkBangaloreKarnataka560071Indiakondtir@gmail.comOrangeRennes35000Francemohamed.boucadair@orange.comCisco Systems, Inc.praspati@cisco.comArbor Networks, Inc.2727 S. State StAnn Arbor, MI48104United Statesandrew@moretension.comVerisign, Inc.United Statesnteague@verisign.comDOTSsecuritymitigationservice deliveryconnectivityanti-DDoSautomationcooperationResilienceFilteringSecurity CenterMitigatorScrubbingdynamic service protectiondynamic mitigationThis document specifies the 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.Please update these statements within the document with the RFC
number to be assigned to this document:"This version of this YANG module is part of RFC XXXX;""RFC XXXX: Distributed Denial-of-Service Open Threat Signaling
(DOTS) Signal Channel Specification";"| [RFCXXXX] |"reference: RFC XXXXPlease update this statement with the RFC number to be assigned to
the following documents:"RFC YYYY: Distributed Denial-of-Service Open Threat Signaling
(DOTS) Data Channel Specification (used to be
I-D.ietf-dots-data-channel)Please update TBD/TBD1/TBD2 statements with the assignments made by
IANA to DOTS Signal Channel Protocol.Also, please update the "revision" date of the YANG modules.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 limited
resources of 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 , 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, besides
likely performance impacts. The firewall then runs out of memory, and
can no longer instantiate the states required to process legitimate
flows. Other possible DDoS attacks are discussed in .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 .An example of a network diagram that illustrates a deployment of DOTS
agents is shown in . 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).DOTS servers can also be reachable over the Internet, as depicted in
.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 protecting 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 (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.The document adheres to the DOTS architecture . The requirements for DOTS
signal channel protocol are documented in . This document satisfies all
the use cases discussed in .This document focuses on the DOTS signal channel. This is a companion
document of the DOTS data channel specification that defines a configuration
and a bulk data exchange mechanism supporting the DOTS signal
channel.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
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
and Datagram Transport Layer Security .
Specific terms are used for any statement that applies to either
protocol alone.The reader should be familiar with the terms defined in .The meaning of the symbols in YANG tree diagrams is defined in .The DOTS signal channel is built on top of the Constrained
Application Protocol (CoAP) , 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) makes it a good candidate to build
the DOTS signaling mechanism from.The DOTS signal channel is layered on existing standards ().In some cases, a DOTS client and server may have mutual agreement to
use a specific port number, such as by explicit configuration or dynamic
discovery . Absent
such mutual agreement, the DOTS signal channel MUST run over port number
TBD as defined in , for both UDP and TCP. In
order to use a distinct port number (as opposed to TBD), DOTS clients
and servers SHOULD support a configurable parameter to supply the port
number to use. The rationale for not using the default port number 5684
((D)TLS CoAP) is to allow for differentiated behaviors in environments
where both a DOTS gateway and an IoT gateway (e.g., Figure 3 of ) are present.The signal channel uses the "coaps" URI scheme defined in Section 6
of and the "coaps+tcp" URI scheme defined
in Section 8.2 of to identify DOTS server
resources 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 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 (). Once the signal channel is established, the
DOTS agents periodically send heartbeats to keep the channel active
(). At any time, the DOTS client may send a
mitigation request message () 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 pre-configured
mitigation requests (if any). DOTS signaling can happen with DTLS over UDP and TLS over TCP.
Likewise, DOTS requests may be sent using IPv4 or IPv6 transfer
capabilities. A Happy Eyeballs procedure for DOTS signal channel is
specified in .A DOTS client is entitled to access only to resources it creates. In
particular, a DOTS client can not 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) , a
binary encoding scheme designed for small code and message size.
CBOR-encoded payloads are used to carry signal channel-specific payload
messages which convey request parameters and response information such
as errors. In order to allow reusing data models across protocols, specifies the JavaScript Object Notation (JSON)
encoding of YANG-modeled data. A similar effort for CBOR is defined in
.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 ().This document specifies a YANG module for representing DOTS
mitigation scopes, DOTS signal channel session configuration data, and
DOTS redirected signaling (). All parameters
in the payload of the DOTS signal channel are mapped to CBOR types as
specified in Table 4.In order to prevent fragmentation, DOTS agents must follow the
recommendations documented in Section 4.6 of . Refer to 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
). The Diagnostic Payload may contain
additional information to aid troubleshooting.In deployments where multiple DOTS clients are enabled in a network
(owned and operated by the same entity), the DOTS server may detect
conflicting mitigation requests from these clients. This document does
not aim to specify a comprehensive list of conditions under which a DOTS
server will characterize two mitigation requests from distinct DOTS
clients as conflicting, nor recommend a DOTS server behavior for
processing conflicting mitigation requests. Those considerations are
implementation- and deployment-specific. Nevertheless, the document
specifies the mechanisms to notify DOTS clients when conflicts occur,
including the conflict cause ().In deployments where one or more translators (e.g., Traditional NAT
, CGN ,
NAT64 , NPTv6 ) are enabled between the client's network and
the DOTS server, DOTS signal channel messages forwarded to a DOTS server
MUST NOT include internal IP addresses/prefixes and/or port numbers;
external addresses/prefixes and/or port numbers as assigned by the
translator MUST be used instead. This document does not make any
recommendation about possible translator discovery mechanisms. The
following are some (non-exhaustive) deployment examples that may be
considered: Port Control Protocol (PCP) or
Session Traversal Utilities for NAT (STUN) may be used 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.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.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 ). The
description of such means is out of scope of this document.Likewise, it is out of scope of this document to specify the
behavior to be followed by a DOTS client 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. ).The DOTS server MUST support the use of the path-prefix of
"/.well-known/" as defined in and the
registered name of "dots". Each DOTS operation is indicated by a
path-suffix that indicates the intended operation. The operation path
() is appended to the path-prefix to form
the URI used with a CoAP request to perform the desired DOTS
operation.OperationOperation PathDetailsMitigation/mitigateSession configuration/config 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 (), each of which can be used to contact the
DOTS server using UDP and TCP. The following specifies the procedure
to follow to select the address family and the transport protocol for
sending DOTS signal channel messages.Such procedure is needed to avoid experiencing long connection
delays. For example, if an IPv4 path to reach a DOTS server is
functional, but the DOTS server's IPv6 path is non-functional, 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 and, as a
consequence, 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 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 .
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 difference in behavior
with respect to the Happy Eyeballs mechanism are listed below:The order of preference of the DOTS signal channel address
family and transport protocol (most preferred first) is: UDP over
IPv6, UDP over IPv4, TCP over IPv6, and finally TCP over IPv4.
This order adheres to the address preference order specified in
and the DOTS signal channel
preference which privileges the use of UDP over TCP (to avoid
TCP's head of line blocking).The DOTS client after successfully establishing a connection
MUST cache information regarding the outcome of each connection
attempt for a specific time period, and 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 mn). Typically, if
the DOTS client has to re-establish the connection with the same
DOTS server within few seconds after the Happy Eyeballs mechanism
is completed, caching avoids trashing the network especially in
the presence of DDoS attack traffic.If 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 becomes available from the DOTS server, 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" set to
100 ms.In reference to , the DOTS
client proceeds with the connection attempts following the rules in
. In this example, it is assumed that
the IPv6 path is broken and UDP traffic is dropped by a middlebox but
has little impact to the DOTS client because there is no long delay
before using IPv4 and TCP.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 re-use the (D)TLS session.The following methods are used by a DOTS client to request,
withdraw, or retrieve the status of mitigation requests:DOTS clients use the PUT method to request
mitigation from a DOTS server ().
During active mitigation, DOTS clients may use PUT requests to
carry mitigation efficacy updates to the DOTS server ().DOTS clients may use the GET method to
subscribe to DOTS server status messages, or to retrieve the list
of its mitigations maintained by a DOTS server ().DOTS clients use the DELETE method to
withdraw a request for mitigation from a DOTS server ().Mitigation request and response messages are marked as
Non-confirmable messages (Section 2.2 of ).DOTS agents MUST follow the data transmission guidelines discussed
in Section 3.1.3 of and control
transmission behavior by not sending more than one UDP datagram per
round-trip time (RTT) to the peer DOTS agent on average.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 ).JSON encoding of YANG modelled data
is used to illustrate the various methods defined in the following
sub-sections. Also, the examples use the Labels defined in Sections
, , , and
.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 and ).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.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 are as follows: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 ,
implementations SHOULD set 'cuid' to the output of a
cryptographic hash algorithm whose input is the Distinguished
Encoding Rules (DER)-encoded Abstract Syntax Notation One
(ASN.1) representation of the Subject Public Key Info (SPKI) of
the DOTS client X.509 certificate , the DOTS client raw public key , or the "Pre-Shared Key (PSK) identity"
used by the DOTS client in the TLS ClientKeyExchange message. In
this version of the specification, the cryptographic hash
algorithm used is SHA-256 . The
output of the cryptographic hash 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 ) with the trailing "=" removed from the
encoding.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 re-install 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 ). 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.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
maintains mitigation requests with pre-configured scopes, it
MUST re-create 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
(). The schema in uses the types defined in . Note that this figure (and other similar
figures depicting a schema) are non-normative sketches of the
structure of the message.The parameters in the CBOR body ()
of the PUT request are described below:A list of prefixes identifying
resources under attack. Prefixes are represented using Classless
Inter-Domain Routing (CIDR) notation . 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 as 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.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) , or Datagram
Congestion Control Protocol (DCCP) , a range of ports can be, for example,
0-1023, 1024-65535, or 1024-49151. This
is an optional attribute.A list of protocols involved in
an attack. Values are taken from the IANA protocol registry
. If 'target-protocol' is not specified, then the
request applies to any protocol. This
is an optional attribute.A list of Fully Qualified Domain
Names (FQDNs) identifying resources under attack .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-prefix'.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.A list of Uniform Resource
Identifiers (URIs) 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.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 ), 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 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. Upon the expiry of this
lifetime, and if the request is not refreshed, the mitigation
request is removed. The request can be refreshed by sending the
same request again. 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 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.The DOTS server MUST always
indicate the actual lifetime in the response and the remaining
lifetime in status messages sent to the DOTS client. This is a mandatory attribute.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 .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.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 to enforce 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. shows an example of a request
relayed by a server-domain DOTS gateway.A server-domain DOTS gateway SHOULD add the following Uri-Path
parameter: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 if the DOTS message was relayed by a
client-domain DOTS gateway or the 'cuid' was generated from a
rogue DOTS client. If a DOTS client is
provisioned, for example, with distinct certificates as a
function of the peer server-domain DOTS gateway, distinct 'cdid'
values may be supplied by a server-domain DOTS gateway. 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 MAY add the CoAP Hop-Limit Option .Because of the complexity to handle partial failure cases, this
specification does not allow for including 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 an URI resolves represent the
'target-prefix', the URI scheme represents the 'target-protocol',
the port subcomponent of authority component of an 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.Attributes and Uri-Path parameters with empty values MUST NOT be
present in a request and render the entire request invalid. shows a PUT request example to
signal that TCP port numbers 80, 8080, and 443 used by
2001:db8:6401::1 and 2001:db8:6401::2 servers are under attack. 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.The corresponding CBOR encoding format for the payload is shown
in .In both DOTS signal and data channel sessions, the DOTS client
MUST authenticate itself to the DOTS server (). The DOTS server MAY use the algorithm
presented in Section 7 of 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.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 in '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 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. 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.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
().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 could 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, having 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-name. To avoid maintaining a
long list of overlapping mitigation requests (i.e., requests with
the same 'trigger-mitigation' type and overlapping scopes) from a
DOTS client and 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 which
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 includes enough information for a DOTS
client to recognize the source of the conflict as described below in
the 'conflict-information' subtree with only the relevant nodes
listed:Indicates that a mitigation
request is conflicting with another mitigation request. This
optional attribute has the following structure: Indicates the cause of the
conflict. The following values are defined:Overlapping targets. 'conflict-scope' provides more
details about the conflicting target clauses.Characterizes the exact
conflict scope. It may include a list of IP addresses, a
list of prefixes, a list of port numbers, a list of target
protocols, a list of FQDNs, a list of URIs, a list of
alias-names, or a 'mid'.If the DOTS server receives a mitigation request which overlaps
with an active mitigation request, but both having 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 ) 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
overlapping with mitigation requests having 'trigger-mitigation' set
to false from that DOTS client, as the loss of the session
implictily activates these preconfigured mitigation requests and
they take precedence. Note that active-but-terminating period is not
observed for mitigations withdrawn at the initiative of the DOTS
server.DOTS clients may adopt various strategies for setting the scopes
of immediate and pre-configured mitigation requests to avoid
potential conflicts. For example, a DOTS client may tweak
pre-configured scopes so that the scope of any overlapping immediate
mitigation request will be a subset of the pre-configured scopes.
Also, if an immediate mitigation request overlaps with any of the
pre-configured scopes, the DOTS client sets the scope of the
overlapping immediate mitigation request to be a subset of the
pre-configured scopes, so as to get a broad mitigation when the DOTS
signal channel collapses and maximize the chance of recovery.If the request is conflicting 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
includes enough information for a DOTS client to recognize the
source of the conflict as described below:Indicates that a mitigation
request is conflicting with another mitigation request(s) from
other DOTS client(s). This optional attribute has the following
structure: Indicates the status of a
conflicting mitigation request. The following values are
defined: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.DOTS server has detected conflicting mitigation
requests from different DOTS clients. This mitigation
request is currently active.DOTS server has detected conflicting mitigation
requests from different DOTS clients. All conflicting
mitigation requests are inactive.Indicates the cause of the
conflict. The following values are defined:Overlapping targets. 'conflict-scope' provides more
details about the conflicting target clauses.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.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 ). Note that
'conflict-status', 'conflict-scope', and 'retry-timer'
MUST NOT be returned in the error response.Characterizes the exact
conflict scope. It may include a list of IP addresses, a
list of prefixes, a list of port numbers, a list of target
protocols, a list of FQDNs, a list of URIs, a list of
alias-names, or references to conflicting ACLs (by an
'acl-name', typically ).Indicates, in seconds, the time
after which the DOTS client may re-issue 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), 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. 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 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 case, the DOTS server MAY update the mitigation
request, 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). 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 'cdid' parameter by
server-domain DOTS gateways specified in
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 the
following table 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.ValueDescriptioncReturn only configuration descendant data nodesnReturn only non-configuration descendant data nodesaReturn all descendant data nodesThe DOTS client can use Block-wise transfer to get the list of all its mitigations
maintained by a DOTS server, it can send 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 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: shows the example of a GET
request to retrieve all DOTS mitigation requests signaled by a
DOTS client. 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 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.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'. 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.The mitigation status parameters are described below:Mitigation start time is
expressed in seconds relative to 1970-01-01T00:00Z in UTC time
(Section 2.4.1 of ). 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.The remaining lifetime of the mitigation
request, in seconds.This is a mandatory
attribute.Status of attack mitigation. The various
possible values of 'status' parameter are explained in .This is a
mandatory attribute.The total dropped byte count for
the mitigation request since the attack mitigation is triggered.
The count wraps around when it reaches the maximum value of
unsigned integer64. This is an optional
attribute.The average number of dropped bytes
per second for the mitigation request since the attack
mitigation is 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.The total number of dropped packet
count for the mitigation request since the attack mitigation is
triggered. The count wraps around when it reaches the maximum
value of unsigned integer64.This is an
optional attribute.The average number of dropped packets
per second for the mitigation request since the attack
mitigation is 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.Parameter ValueDescription1Attack mitigation setup is in progress (e.g., changing the
network path to redirect the inbound traffic to a DOTS
mitigator).2Attack is being successfully mitigated (e.g., traffic is
redirected to a DDoS mitigator and attack traffic is dropped).3Attack 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 pre-configured
scopes (i.e., 'trigger-mitigation' set to 'false'), this status
code will be transmitted 4 times and then transition to "8".4Attack has exceeded the mitigation provider capability.5DOTS client has withdrawn the mitigation request and the
mitigation is active but terminating.6Attack mitigation is now terminated.7Attack 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 4 times and then
transition to "8" for the mitigation request with pre-configured
scopes.8Attack mitigation will be triggered for the mitigation request
only when the DOTS signal channel session is lost.The Observe Option defined in
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 use the Observe Option for
both 'mitigate' and 'config' ().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. 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 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.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 ).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 it is a default behavior of the DOTS server
implementation. Then, the DOTS server sends notification
message(s) to the DOTS client(s) at the origin of the conflict
(refer to the conflict parameters defined in ). A conflict notification message includes
information about the conflict cause, scope, and the status of the
mitigation request(s). For example,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.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 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 deregister itself by issuing a GET request that has the
Token field set to the token of the observation to be cancelled
and includes an Observe Option with the value set to '1'
(deregister). The latter is RECOMMENDED. shows an example of a DOTS
client requesting a DOTS server to send notifications related to a
mitigation request. Note that for mitigations with pre-configured
scopes (i.e., 'trigger-mitigation' set to 'false'), the state will
need to transition from 3 (attack-stopped) to 8
(attack-mitigation-signal-loss).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. Absent such policy, the frequency of polling
the DOTS server to get the mitigation status SHOULD follow the
transmission guidelines in Section 3.1.3 of .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 recalls the mitigation
request by issuing a DELETE request for this mitigation request
().A DOTS client SHOULD react to the status of the attack as per
the information sent by the DOTS server rather than performing its
own detection that the attack has been mitigated. This ensures
that the DOTS client does not recall 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.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 PUT request used for efficacy update MUST include all the
parameters used in the PUT request to carry the DOTS mitigation
request () 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 ) 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 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 .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 .Parameter valueDescription1The DOTS client determines that it is still under attack.2The DOTS client determines that the attack is successfully
mitigated (e.g., attack traffic is not seen).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
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 , 5.03
uses Max-Age option to indicate the number of seconds after which to
retry.DELETE requests are used to withdraw DOTS mitigation requests
from DOTS servers ().'cuid' and 'mid' are mandatory Uri-Path parameters for DELETE
requests.The same considerations for manipulating 'cdid' parameter by DOTS
gateways, as specified in , MUST be
followed for DELETE requests. Uri-Path parameters with empty values
MUST NOT be present in a request.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 signal
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 ().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, as the DOTS client is no
longer responsible for the mitigation.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.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: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.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.Acceptable signal loss ratio: Maximum retransmissions,
retransmission timeout value, and other message transmission
parameters for the DOTS signal channel.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), 'idle-config'-related values 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 'idle-config' to 'mitigating-config'-related
values).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 , a Confirmable message is retransmitted using
a default timeout and exponential back-off 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 . 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 . 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 ). Requests and responses exchanged between
DOTS agents during 'idle' time are marked as Confirmable
messages.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 for more details).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. shows how to obtain acceptable
configuration parameters for the DOTS server.The DOTS server in the 2.05 (Content) response conveys the
current, minimum, and maximum attribute values acceptable by the
DOTS server ().The parameters in are described
below:Set of configuration parameters
to use when a mitigation is active. The following parameters may
be included: Time interval in seconds
between two consecutive heartbeat messages. '0' is used to disable the heartbeat
mechanism. This is an optional
attribute.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.Maximum number of
retransmissions for a message (referred to as MAX_RETRANSMIT
parameter in CoAP). This is an
optional attribute.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.Random factor used to
influence the timing of retransmissions (referred to as
ACK_RANDOM_FACTOR parameter in CoAP). This is an optional attribute.Set of configuration parameters to
use when no mitigation is active. This attribute has the same
structure as 'mitigating-config'. 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.A PUT request (Figures and ) 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 . The
RECOMMENDED values of transmission parameter values are ack-timeout
(2 seconds), max-retransmit (3), 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' (5). Note: heartbeat-interval should be tweaked to also assist
DOTS messages for NAT traversal (SIG-011 of ). According to , keepalive messages must not be sent
more frequently than once every 15 seconds and should use longer
intervals when possible. Furthermore, recommends NATs to 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 as too
chatty in some deployments. For such deployments, DOTS agents
may negotiate longer heartbeat-interval values to prevent any
network overload with too frequent keepalives.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 is also smaller than
the translator session timeout to prevent translator traversal
issues, or disabled entirely. Means to discover the lifetime
assigned by a translator are out of scope.Section 4.2 of defines a
“CoAP Ping” mechanism. Concretely, the DOTS agent sends
an Empty Confirmable message and the peer DOTS agent will respond by
sending a Reset message.When a Confirmable "CoAP Ping" is sent, and if there is no
response, the "CoAP Ping" is retransmitted max-retransmit number of
times by the CoAP layer using an initial timeout set to a random
duration between ack-timeout and (ack-timeout*ack-random-factor) and
exponential back-off between retransmissions. By choosing the
recommended transmission parameters, the "CoAP Ping" will timeout
after 45 seconds. If the DOTS agent does not receive any response
from the peer DOTS agent for 'missing-hb-allowed' number of
consecutive "CoAP Ping" Confirmable messages, it concludes that the
DOTS signal channel session is disconnected. A DOTS client MUST NOT
transmit a "CoAP Ping" while waiting for the previous "CoAP Ping"
response from the same DOTS server.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 . The DOTS agents
MUST use the negotiated values for message transmission parameters
and default values for non-negotiated message transmission
parameters.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.The additional Uri-Path parameter to those defined in is as follows: 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.The meaning of the parameters in the CBOR body () is defined in .At least one of the attributes 'heartbeat-interval',
'missing-hb-allowed', 'max-retransmit', 'ack-timeout', and
'ack-random-factor' MUST be present in the PUT request. Note that
'heartbeat-interval', 'missing-hb-allowed', '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.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. 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. 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 '91' when a
mitigation is active.The DOTS server indicates the result of processing the PUT
request using CoAP response codes: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.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.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.If any of the 'heartbeat-interval', 'missing-hb-allowed',
'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 ().The DOTS
client may re-try and send the PUT request with updated
attribute values acceptable to the DOTS server.A DOTS client may issue a GET message with 'sid' Uri-Path
parameter to retrieve the negotiated configuration. The response
does not need to include 'sid' in its message body.Max-Age Option (Section 5.10.5 of )
SHOULD be returned by a DOTS server to associate a validity time
with a configuration it sends. This feature allows the update of the
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 'sid' Uri-Path parameter to
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 as 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 ). 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 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 ).If a DOTS server detects that a misbehaving DOTS client does not
contact the DOTS server after the expiry of Max-Age and 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 )).A DELETE request is used to delete the installed DOTS signal
channel session configuration data ().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'.Redirected DOTS signaling is discussed in detail in Section 3.2.2
of .If a DOTS server wants to redirect a DOTS client to an alternative
DOTS server for a signal session, then the response code 5.03 (Service
Unavailable) will be returned in the response to the DOTS client.The DOTS server can return the error response code 5.03 in response
to a request from the DOTS client or convey the error response code
5.03 in a unidirectional notification response from the DOTS
server.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 ().The parameters are described below:FQDN of an alternate DOTS server.
This is a mandatory attribute.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 which encloses an alternate server.A Max-Age Option set to '0' may be returned for redirecting
mitigation requests. Such value means that the redirection applies
only for the mitigation request in progress. Returning short TTL in 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
. This fall back mechanism is triggered
immediately upon expiry of the TTL, except when a DDoS attack is
active.Requests issued by misbehaving DOTS clients which do not honor the
TTL conveyed in the Max-Age Option or react to explicit re-direct
messages can be rejected by DOTS servers. 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.When the DOTS client receives 5.03 response with an alternate
server included, it considers the current request as failed, but
SHOULD try re-sending the request to the alternate DOTS server. During
a DDoS attack, the DNS server may be the target of another DDoS
attack, alternate DOTS server's IP addresses conveyed in the 5.03
response help the DOTS client skip 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. The DOTS client MAY
implement a method to construct IPv4-embedded IPv6 addresses ; 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 to which it
has already communicated with 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 . It is RECOMMENDED
that DOTS clients support means to alert administrators about redirect
loops.To provide an indication of signal health and 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 ). The DOTS agent similarly
expects a heartbeat from its peer DOTS agent, and 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 firewalls and/or stateful translators bindings
alive. This probing reduces the frequency of establishing a new
handshake when a DOTS signal needs to be conveyed to the DOTS
server.DOTS servers MAY trigger their heartbeat requests immediately after
receiving heartbeat probes from peer DOTS clients. As a reminder, 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.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, the DOTS agents 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 resume the (D)TLS
session. The DOTS client SHOULD send mitigation requests over the
current DOTS signal channel session, and in parallel, for example,
try to resume the (D)TLS session or use 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 (D)TLS session resumption or if (D)TLS session resumption 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 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 the DOTS client is under attack and 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 the DOTS client has not
detected the attack or, if an attack mitigation is in progress, it
implies the applied DDoS mitigation actions are not yet effective
to handle the DDoS attack volume. If the DOTS server does not receive any traffic from the peer
DOTS client, then the DOTS server sends heartbeat requests to the
DOTS client and after maximum 'missing-hb-allowed' threshold is
reached, the DOTS server concludes the session is disconnected.
The DOTS server can then trigger pre-configured mitigation
requests for this DOTS client (if any).In DOTS over UDP, heartbeat messages MUST be exchanged between the
DOTS agents using the “CoAP Ping” mechanism defined in
Section 4.2 of .In DOTS over TCP, heartbeat messages MUST be exchanged between the
DOTS agents using the Ping and Pong messages specified in Section 5.4
of . That is, the DOTS agent sends a
Ping message and the peer DOTS agent would respond by sending a single
Pong message.This document defines a YANG module
for DOTS mitigation scope, DOTS signal channel session configuration
data, and DOTS redirection signaling.This YANG module (ietf-dots-signal-channel) defines the DOTS client
interaction with the DOTS server as seen by the DOTS client. A DOTS
server is allowed to update the non-configurable 'ro' entities in the
responses. This YANG module is not intended to be used via
NETCONF/RESTCONF for DOTS server management purposes; such module is out
of the scope of this document. It serves only to provide a data model
and encoding, but not a management data model.A companion YANG module is defined to include a collection of types
defined by IANA: "iana-dots-signal-channel" ().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,
or a redirect message.This module uses the common YANG types defined in and types defined in .All parameters in the payload of the DOTS signal channel MUST be
mapped to CBOR types as shown in Table 4 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 4.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
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.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 except with respect
to (D)TLS version. Since DOTS signal channel encryption relying upon
(D)TLS is virtually a green-field 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 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 . Additionally, the DOTS client
MUST use 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 server 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 ) 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 clients
to enable the required mutual authentication of DOTS agents.
Enrollment over Secure Transport (EST)
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 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 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:DTLS record replay detection (Section 3.3 of ) or an equivalent mechanism to protect
against replay attacks.DTLS session resumption without server-side state to resume
session and convey the DOTS signal.At least one of raw public keys
or PSK handshake with (EC)DHE key
exchange which reduces the size of the ServerHello, and 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:TLS False Start 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.Cached Information Extension
which avoids transmitting the server's certificate and certificate
chain if the client has cached that information from a previous
TLS handshake.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 to eliminate that RTT.TLS 1.3 provides critical latency improvements for connection
establishment over TLS 1.2. The DTLS 1.3 protocol 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: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.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 discusses some mechanisms to implement 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
) is changed each time a new CoAP
request is sent, and the Token (Section 5.3.1 of ) 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 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 , DOTS servers couple the DOTS signal channel
sessions using the DOTS client identity and optionally the 'cdid'
parameter value. Furthermore, 'mid' value is monotonically
increased by the DOTS client for each mitigation request,
attackers replaying 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, 'sid' value is monotonically increased by
the DOTS client for each configuration request (), 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 for more details.
A simplified TLS 1.3 handshake with 0-RTT
DOTS mitigation request message exchange is shown in .To avoid DOTS signal message fragmentation and the subsequent
decreased probability of message delivery, DOTS agents MUST ensure
that the DTLS record fit within a single datagram. If the 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 . If IPv4
support on legacy or otherwise unusual networks is a consideration and
the PMTU is unknown, DOTS implementations MAY assume on a PMTU of 576
bytes for IPv4 datagrams, as every IPv4 host must be capable of
receiving a packet whose length is equal to 576 bytes as discussed in
and .The DOTS client must consider the amount of record expansion
expected by the DTLS processing when calculating the size of CoAP
message that fits within the path MTU. Path MTU 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 ). If the
total request size exceeds the path MTU 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 path MTU is unknown, implementations may
want to limit themselves to more conservative IPv4 datagram sizes such
as 576 bytes, as per .(D)TLS based upon client certificate 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 DOTS
client. DOTS client certificate validation must be performed as per
and the DOTS client certificate must
conform to the certificate profile. If a
DOTS client does not support TLS client certificate authentication, it
must support pre-shared key based or raw public key based client
authentication.In the example depicted in , the DOTS
gateway and DOTS clients within the 'example.com' domain mutually
authenticate. 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 , the DOTS server only allows the DOTS gateway
to request mitigation for 'example.com' domain and not for other
domains.IANA is requested to assign the port number TBD 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/service-names-port-numbers.xhtml.The assignment of port number 4646 is strongly suggested, as 4646
is the ASCII decimal value for ".." (DOTS).This document requests IANA to register the 'dots' well-known URI
(Table 5) in the Well-Known URIs registry
(https://www.iana.org/assignments/well-known-uris/well-known-uris.xhtml)
as defined by :This document requests IANA to register the application/dots+cbor
media type in the "Media Types" registry in the manner described in , which can be used to indicate that the
content is a DOTS signal channel object: Type name: applicationSubtype name: dots+cborRequired parameters: N/AOptional parameters: N/AEncoding considerations: binarySecurity considerations: See the Security Considerations
section of [RFCXXXX]Interoperability considerations: N/APublished specification: [RFCXXXX]Applications that use this media type: DOTS agents sending DOTS
messages over CoAP over (D)TLS.Fragment identifier considerations: N/AAdditional information:Magic number(s): N/AFile extension(s): N/AMacintosh file type code(s): N/APerson & email address to contact for further information:
IESG, iesg@ietf.orgIntended usage: COMMONRestrictions on usage: noneAuthor: See Authors' Addresses section.Change controller: IESGProvisional registration? NoThis document requests IANA to register the CoAP Content-Format ID
for the "application/dots+cbor" media type in the "CoAP
Content-Formats" registry (0-255 range):Media Type: application/dots+cborEncoding: -Id: TBD1Reference: [RFCXXXX]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. 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.This document requests IANA to register the DOTS signal channel
CBOR tag in the "CBOR Tags" registry using the 24-255 range:CBOR Tag: TBD2 (please assign the same value as the
Content-Format)Data Item: DDoS Open Threat Signaling (DOTS) signal channel
objectSemantics: DDoS Open Threat Signaling (DOTS) signal channel
object, as defined in [RFCXXXX]Description of Semantics: [RFCXXXX]The document requests IANA to create a new registry, entitled "DOTS
Signal Channel Registry". The following sections define
sub-registries.The document requests IANA to create a new sub-registry, entitled
"DOTS Signal Channel CBOR Key Values".The structure of this sub-registry is provided in . provides how
the registry is initially populated with the values in Table 4.Parameter name as used
in the DOTS signal channel.Key value for the
parameter. The key value MUST be an integer in the 1-65535
range. The key values of the comprehension-required range
(0x0001 - 0x3FFF) and of the comprehension-optional range
(0x8000 - 0xBFFF) are assigned by IETF Review (Section 4.8 of
). The key values of the
comprehension-optional range (0x4000 - 0x7FFF) are assigned by
Specification Required (Section 4.6 of ) and of the comprehension-optional
range (0xC000 - 0xFFFF) are reserved for Private Use (Section
4.1 of ).Registration requests for the 0x4000 - 0x7FFF
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 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 includes 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 the
registration description is clear. IANA must only accept
registry updates to the 0x4000 - 0x7FFF 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 and
optional tag for the parameter.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.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.The document requests IANA to create a new sub-registry, entitled
"DOTS Signal Channel Status Codes". Codes in this registry are used
as valid values of 'status' parameter.The registry is initially populated with the following
values:CodeLabelDescriptionReference1attack-mitigation-in-progressAttack mitigation setup is in progress (e.g., changing the
network path to redirect the inbound traffic to a DOTS
mitigator).[RFCXXXX]2attack-successfully-mitigatedAttack is being successfully mitigated (e.g., traffic is
redirected to a DDoS mitigator and attack traffic is dropped).[RFCXXXX]3attack-stoppedAttack has stopped and the DOTS client can withdraw the
mitigation request.[RFCXXXX]4attack-exceeded-capabilityAttack has exceeded the mitigation provider capability.[RFCXXXX]5dots-client-withdrawn-mitigationDOTS client has withdrawn the mitigation request and the
mitigation is active but terminating.[RFCXXXX]6attack-mitigation-terminatedAttack mitigation is now terminated.[RFCXXXX]7attack-mitigation-withdrawnAttack mitigation is withdrawn.[RFCXXXX]8attack-mitigation-signal-lossAttack mitigation will be triggered for the mitigation request
only when the DOTS signal channel session is lost.[RFCXXXX]New codes can be assigned via Standards Action .The document requests IANA to create a new sub-registry, entitled
"DOTS Signal Channel Conflict Status Codes". Codes in this registry
are used as valid values of 'conflict-status' parameter.The registry is initially populated with the following
values:CodeLabelDescriptionReference1request-inactive-other-activeDOTS 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.[RFCXXXX]2request-activeDOTS server has detected conflicting mitigation requests from
different DOTS clients. This mitigation request is currently
active.[RFCXXXX]3all-requests-inactiveDOTS server has detected conflicting mitigation requests from
different DOTS clients. All conflicting mitigation requests are
inactive.[RFCXXXX]New codes can be assigned via Standards Action .The document requests IANA to create a new sub-registry, entitled
"DOTS Signal Channel Conflict Cause Codes". Codes in this registry
are used as valid values of 'conflict-cause' parameter.The registry is initially populated with the following
values:CodeLabelDescriptionReference1overlapping-targetsOverlapping targets.[RFCXXXX]2conflict-with-acceptlistConflicts 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.[RFCXXXX]3cuid-collisionCUID Collision. This code is returned when a DOTS client uses a
'cuid' that is already used by another DOTS client.[RFCXXXX]New codes can be assigned via Standards Action .The document requests IANA to create a new sub-registry, entitled
"DOTS Signal Channel Attack Status Codes". Codes in this registry
are used as valid values of 'attack-status' parameter.The registry is initially populated with the following
values:CodeLabelDescriptionReference1under-attackThe DOTS client determines that it is still under attack.[RFCXXXX]2attack-successfully-mitigatedThe DOTS client determines that the attack is successfully
mitigated.[RFCXXXX]New codes can be assigned via Standards Action .This document requests IANA to register the following URIs in the
"ns" subregistry within the "IETF XML Registry" : This document requests IANA to register the following YANG
modules in the "YANG Module Names" subregistry within the "YANG Parameters" registry.This document defines the initial version of the IANA-maintained
iana-dots-signal-channel YANG module. IANA is requested to add 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:Replicates the label from the
registry.Contains the IANA-assigned value
corresponding to the 'status', 'conflict-status',
'conflict-cause', or 'attack-status'.Replicates the description
from the registry.Replicates the reference from
the registry and add 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 add this note to "DOTS Status Codes", "DOTS
Conflict Status Codes", "DOTS Conflict Cause Codes", and "DOTS Attack
Status Codes" registries:When this registry is modified, the YANG module
iana-dots-signal-channel must be updated as defined in
[RFCXXXX].High-level DOTS security considerations are documented in and .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 MUST be followed to
avoid attacks on (D)TLS. The (D)TLS protocol profile used for the DOTS
signal channel is specified in .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-AO . 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.An attack vector that can be achieved if the 'cuid' is guessable is a
misbehaving DOTS client from within the client's domain which uses the
'cuid' of another DOTS client of the domain to delete or alter active
mitigations. For this attack vector to happen, the misbehaving client
needs to pass the security validation checks by the DOTS server, and
eventually the checks of a client-domain DOTS gateway.A similar attack can be achieved by a compromised DOTS client which
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 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
mitigation request for a target resource, gets the mitigation efficacy
from the DOTS server, and conveys the mitigation efficacy to the DDoS
attacker to possibly change the DDoS attack strategy. Obviously,
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 defends 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-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. That is, only actions on IP
resources that belong to the DOTS client' domain MUST be authorized by a
DOTS server. 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 or DoH ) to
prevent eavesdroppers from possibly identifying the target resources
protected by the DDoS mitigation service, and means to ensure the target
FQDN resolution is authentic (e.g., DNSSEC ).CoAP-specific security considerations are discussed in Section 11 of
, while CBOR-related security
considerations are discussed in Section 8 of .The following individuals have contributed to this document:Jon Shallow, NCC Group, Email: jon.shallow@nccgroup.trustMike Geller, Cisco Systems, Inc. 3250 Florida 33309 USA, Email:
mgeller@cisco.comRobert Moskowitz, HTT Consulting Oak Park, MI 42837 United
States, Email: rgm@htt-consult.comDan Wing, Email: dwing-ietf@fuggles.comThanks 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
Kühlewind, and Alissa Cooper for the review.Media TypesIANACoAP Content-FormatsIANAConcise Binary Object Representation (CBOR) TagsIANAIANA, "Protocol Numbers"The document recommends the use of SPKI to generate the 'cuid'. This
design choice is motivated by the following reasons:SPKI is globally unique.It is deterministic.It allows to avoid extra cycles that may be induced by 'cuid'
collision.DOTS clients do not need to store the 'cuid' in a persistent
storage.It allows to detect compromised DOTS clients that do not adhere
to the 'cuid' generation algorithm.