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 Statesamortensen@arbor.netVerisign, 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 TBD statements with the port number to be
assigned to DOTS Signal Channel Protocol.Also, please update the "revision" date of the YANG module.A distributed denial-of-service (DDoS) attack is an attempt to make
machines or network resources unavailable to their intended users. In
most cases, sufficient scale 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 it can handle, the limited resources
of the control plane, etc. When processing network traffic, such
applications are supposed to use these resources to offer the intended
task 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.TCP DDoS SYN-flood, for example, is a memory-exhausting attack while
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.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 .(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 ().By default, a DOTS signal channel MUST run over port number TBD as
defined in , for both UDP and TCP, unless the
DOTS server has a mutual agreement with its DOTS clients to use a
different port number. DOTS clients MAY alternatively support means to
dynamically discover the ports used by their DOTS servers. 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 "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.The signal channel is initiated by the DOTS client (). 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 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.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 .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 the use of the same data models, specifies the JSON encoding of YANG-modeled
data. A similar effort for CBOR is defined in .From that standpoint, this document specifies a YANG module for
representing DOTS mitigation scopes, DOTS signal channel session
configuration data, and DOTS redirected signalling (). Representing these data as CBOR data is assumed
to follow the rules in or
those in combined with JSON/CBOR
conversion rules in . All parameters in
the payload of the DOTS signal channel are mapped to CBOR types as
specified in .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 and 3.xx Response Codes
MUST be of content type "application/cbor" (Section 5.5.1 of ). 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 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).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/v1/mitigateSession configuration/v1/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 found,
but the DOTS server's IPv6 path is not working, a dual-stack DOTS
client may experience a significant connection delay compared to an
IPv4-only DOTS client. 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 session 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 in a manner similar to
the Happy Eyeballs mechanism . These
connection attempts are performed by the DOTS client when it
initializes. The results of the Happy Eyeballs procedure are used by
the DOTS client for sending its subsequent messages to the DOTS
server.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).In reference to , the DOTS
client sends two TCP SYNs and two DTLS ClientHello messages at the
same time over IPv6 and IPv4. 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. The DOTS client 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.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 SHOULD 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 SHOULD
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 ).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) (, illustrated in JSON
diagnostic notation).If a DOTS client is entitled to solicit the DOTS service, the
DOTS server can enable mitigation on behalf of the DOTS client by
communicating the DOTS client's request to a mitigator and relaying
the feedback of the thus-selected mitigator to the requesting DOTS
client.The Uri-Path option carries a major and minor version
nomenclature to manage versioning; DOTS signal channel in this
specification uses 'v1' major version.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.Implementations SHOULD use the output of a
cryptographic hash algorithm whose input is the DER-encoded
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 "PSK identity" used by the DOTS
client in the TLS ClientKeyExchange message to set 'cuid'. 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.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 per DOTS server. 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. 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.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 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 it is
peace-time, 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 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
(resp. 128) for IPv4 (resp. 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's 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
. The value '0' has a special meaning for 'all
protocols'. This is an optional
attribute.A list of Fully Qualified Domain
Names (FQDNs) identifying resources under attack. An FQDN is the
full name of a resource, rather than just its hostname. For
example, "venera" is a hostname, and "venera.isi.edu" is an FQDN
. 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'.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
expiring the request where the client has unexpectedly quit in a
timely manner. 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 session is lost. 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 SHOULD be
supplied to the DOTS server. That information is meant to assist the
DOTS server to enforce some policies such as correlating 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
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
DOTS gateway or 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.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 'scope' parameters in 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 represent the full scope of the mitigation.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. shows a PUT request example to
signal that ports 80, 8080, and 443 used by 2001:db8:6401::1 and
2001:db8:6401::2 servers are under attack (illustrated in JSON
diagnostic notation). 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 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 has erred 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.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 Vendor-Specific 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.If the DOTS server finds the 'mid' parameter value conveyed in
the PUT request in its configuration data bound to that DOTS client,
it MAY update the mitigation request, and a 2.04 (Changed) response
is returned to indicate a successful update of the mitigation
request.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: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.Indicates the 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 MUST 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 MUST withdraw (absent explicit policy/configuration
otherwise) any active mitigation requests overlapping with
mitigation requests having 'trigger-mitigation' set to false from
that DOTS client. 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.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 white list. This code is
returned when the DDoS mitigation detects source
addresses/prefixes in the white-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. Note that
'conflict-status', 'conflict-scope', and 'retry-timer'
are not returned in the error response.Indicates the 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.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. The lifetime of the
deactivated mitigation request will be updated to
(retry-timer + 45 seconds), so the DOTS client can refresh
the deactivated mitigation request after retry-timer seconds
before expiry of 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.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' (content) parameter and its permitted values defined in
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.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 triggered.
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 SHOULD be a five-minute average.
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 SHOULD be a five-minute average.
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. 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 unsolicited notifications of attack mitigation
status from the DOTS server.Unidirectional mitigation notifications within the
bidirectional signal channel allows unsolicited message delivery,
enabling asynchronous notifications between the agents. indicates that (1) a notification can be
sent in a Confirmable (CON) or a Non-confirmable (NON) 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 SHOULD NOT send more
than one unsolicited 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). 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). 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 acknowledging
by itself, using its own means, 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.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 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. For example, if there is a
financial relationship between the DOTS client and server domains,
the DOTS client stops incurring cost at this point.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 observation of 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 (CoAP Ping/Pong) 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,
'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 a peacetime, the DOTS agent switches from 'idle-config'
to 'mitigating-config'-related values).Requests and responses are deemed reliable 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
message is 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 peacetime are
marked as Confirmable messages.Implementation Note: A DOTS client that receives a response in
a CON 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 CON, 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 an on-path 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 attack and peace times.A PUT request 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, this specification recommends a minimum
heartbeat-interval of 15 seconds and a maximum
heartbeat-interval of 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 set to '0'. Means to discover the lifetime assigned
by a translator are out of scope.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. 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 request 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, in order to
retrieve the signal channel configuration data, it MAY terminate the
(D)TLS session. A (D)TLS session is terminated by the receipt of an
authenticated message that closes the connection (e.g., a fatal
alert (Section 6 of )).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) and time
to live 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. 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. 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.While the communication between the DOTS agents is 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
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 session liveliness during link
saturation:The DOTS client MUST NOT consider the DOTS session terminated
even after a maximum 'missing-hb-allowed' threshold is reached.
The DOTS client SHOULD keep on using the current DOTS session to
send heartbeat requests over it, so that the DOTS server knows the
DOTS client has not disconnected the DOTS 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 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 session, the DOTS client can stop (D)TLS session
resumption or if (D)TLS session resumption is successful then
disconnect the current DOTS session.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.In DOTS over UDP, heartbeat messages MUST be exchanged between the
DOTS agents using the “CoAP Ping” mechanism defined in
Section 4.2 of . Concretely, the DOTS
agent sends an Empty Confirmable message and the peer DOTS agent will
respond by sending a Reset message.In DOTS over TCP, heartbeat messages MUST be exchanged between the
DOTS agents using the Ping and Pong messages specified in Section 4.4
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 redirected signalling.This YANG module 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 for DOTS server management purposes. Such module
is out of the scope of this document.This document defines the YANG module "ietf-dots-signal-channel"
(), which has the following tree
structure. A DOTS signal message can either be a mitigation or a
configuration message.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. The recipient of the payload MAY reject the information
if it is not suitably mapped.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 relies 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 . The DOTS client additionally
uses validation techniques to compare
the domain name with the certificate provided.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. 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 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 ) to protect against replay attacks.DTLS session resumption without server-side state to resume
session and convey the DOTS signal.Raw public keys or PSK handshake
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 second flight of messages
(ChangeCipherSpec) to also contain the DOTS signal.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.TCP Fast Open can reduce the
number of round-trips to convey DOTS signal channel message.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 peacetime 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. 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. A DOTS server can reject
0-RTT by sending a TLS HelloRetryRequest.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 MUST fit within a single datagram. If the path
MTU is not known to the DOTS server, an IP MTU of 1280 bytes SHOULD be
assumed. If UDP is used to convey the DOTS signal messages then 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 overhead of 13 octets + authentication
overhead of the negotiated DTLS cipher suite + block padding] (Section
4.1.1.1 of ). If the 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 IPv4 path MTU is unknown, implementations may want
to limit themselves to more conservative IPv4 datagram sizes such as
576 bytes, as per . IP packets whose
size does not exceed 576 bytes should never need to be fragmented:
therefore, sending a maximum of 500 bytes of DOTS signal over a UDP
datagram will generally avoid IP fragmentation.(D)TLS based upon client certificate can be used for mutual
authentication between DOTS agents. If 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
certificate request 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.This specification registers a service port (), a URI suffix in the Well-Known URIs registry
(), and a YANG module (). It also creates a registry for mappings to CBOR
().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 :The document requests IANA to create a new registry, entitled "DOTS
Signal Channel CBOR Mappings Registry". The structure of this registry
is provided in .The registry is initially populated with the values in Table 6.Values from that registry MUST be assigned via Expert Review .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 in the 32768-65535 range are assigned to
Vendor-Specific parameters.CBOR Major type and
optional tag for the claim.For Standards Track
RFCs, list the "IESG". For others, give the name of the
responsible party. Other details (e.g., postal address, email
address, home page URI) 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.This document requests IANA to register the following URI in the
"IETF XML Registry" : This document requests IANA to register the following YANG
module in the "YANG Module Names" registry .Authenticated encryption MUST be used for data confidentiality and
message integrity. The interaction between the DOTS agents requires
Datagram Transport Layer Security (DTLS) and 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 for DOTS signal
channel is specified in .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.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 . 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.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's 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.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 D. Danyliw,
Michael Richardson, Ehud Doron, Kaname Nishizuka, Dave Dolson, Liang
Xia, Gilbert Clark, and Nesredien Suleiman for the discussion and
comments.Thanks to the core WG for the recommendations on Hop-Limit and
redirect signaling.IANA, "Protocol Numbers"