DOTS T. Reddy
Internet-Draft Cisco
Intended status: Standards Track M. Boucadair
Expires: September 3, 2017 Orange
P. Patil
Cisco
March 2, 2017
Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal
Channel
draft-reddy-dots-signal-channel-09
Abstract
This document specifies a mechanism that a DOTS client can use to
signal that a network is under a Distributed Denial-of-Service (DDoS)
attack to an upstream DOTS server so that appropriate mitigation
actions are undertaken (including, blackhole, drop, rate-limit, or
add to watch list) on the suspect traffic. The document specifies
the DOTS signal channel including Happy Eyeballs considerations. The
specification of the DOTS data channel is elaborated in a companion
document.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 3, 2017.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions and Terminology . . . . . . . . . . . 3
3. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 4
4. Happy Eyeballs for DOTS Signal Channel . . . . . . . . . . . 5
5. DOTS Signal Channel . . . . . . . . . . . . . . . . . . . . . 6
5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. DOTS Signal YANG Model . . . . . . . . . . . . . . . . . 7
5.2.1. Mitigation Request Model structure . . . . . . . . . 7
5.2.2. Mitigation Request Model . . . . . . . . . . . . . . 8
5.2.3. Session Configuration Model structure . . . . . . . . 10
5.2.4. Session Configuration Model . . . . . . . . . . . . . 10
5.3. Mitigation Request . . . . . . . . . . . . . . . . . . . 12
5.3.1. Convey DOTS Signals . . . . . . . . . . . . . . . . . 13
5.3.2. Withdraw a DOTS Signal . . . . . . . . . . . . . . . 18
5.3.3. Retrieving a DOTS Signal . . . . . . . . . . . . . . 19
5.3.4. Efficacy Update from DOTS Client . . . . . . . . . . 23
5.4. DOTS Signal Channel Session Configuration . . . . . . . . 25
5.4.1. Discover Acceptable Configuration Parameters . . . . 25
5.4.2. Convey DOTS Signal Channel Session Configuration . . 26
5.4.3. Delete DOTS Signal Channel Session Configuration . . 29
5.4.4. Retrieving DOTS Signal Channel Session Configuration 29
5.5. Redirected Signaling . . . . . . . . . . . . . . . . . . 30
5.6. Heartbeat Mechanism . . . . . . . . . . . . . . . . . . . 31
6. Mapping parameters to CBOR . . . . . . . . . . . . . . . . . 32
7. (D)TLS Protocol Profile and Performance considerations . . . 32
7.1. MTU and Fragmentation Issues . . . . . . . . . . . . . . 33
8. (D)TLS 1.3 considerations . . . . . . . . . . . . . . . . . . 34
9. Mutual Authentication of DOTS Agents & Authorization of DOTS
Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
10.1. DOTS signal channel CBOR Mappings Registry . . . . . . . 37
10.1.1. Registration Template . . . . . . . . . . . . . . . 37
10.1.2. Initial Registry Contents . . . . . . . . . . . . . 37
11. Security Considerations . . . . . . . . . . . . . . . . . . . 41
12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 41
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 42
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 42
14.1. Normative References . . . . . . . . . . . . . . . . . . 42
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14.2. Informative References . . . . . . . . . . . . . . . . . 43
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 45
1. Introduction
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.
In many cases, it may not be possible for an network administrators
to determine the causes of an attack, but instead just realize that
certain resources seem to be under attack. This document, which
adheres to the DOTS architecture [I-D.ietf-dots-architecture],
proposes that, in such cases, the DOTS client just inform its DOTS
server(s) that the network is under a potential attack and that the
mitigator monitors traffic to the network to mitigate any possible
attacks. This cooperation between DOTS agents contributes to ensure
a highly automated network that is also robust, reliable and secure.
Protocol requirements for DOTS signal channel are obtained from DOTS
requirements [I-D.ietf-dots-requirements].
This document satisfies all the use cases discussed in
[I-D.ietf-dots-use-cases] except the Third-party DOTS notifications
use case in Section 3.2.3 of [I-D.ietf-dots-use-cases] which is an
optional feature and not a core use case. Third-party DOTS
notifications are not part of the DOTS requirements document.
Moreover, the DOTS architecture does not assess whether that use case
may have an impact on the architecture itself and/or the DOTS trust
model.
This is a companion document to the DOTS data channel specification
[I-D.reddy-dots-data-channel].
2. Notational Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
(D)TLS: For brevity this term is used for statements that apply to
both Transport Layer Security [RFC5246] and Datagram Transport Layer
Security [RFC6347]. Specific terms will be used for any statement
that applies to either protocol alone.
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The reader should be familiar with the terms defined in
[I-D.ietf-dots-architecture].
3. Solution Overview
Network applications have finite resources like CPU cycles, number of
processes or threads they can create and use, maximum number of
simultaneous connections it can handle, 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 fashion. However, an attacker
may be able to prevent an application from performing its intended
task by causing the application to exhaust the finite supply of a
specific resource.
TCP DDoS SYN-flood, for example, is a memory-exhaustion attack on the
victim and ACK-flood is a CPU exhaustion attack on the victim
([RFC4987]). Attacks on the link are carried out by sending enough
traffic such that the link becomes excessively congested, and
legitimate traffic suffers high packet loss. Stateful firewalls can
also be attacked by sending traffic that causes the firewall to hold
excessive state and the firewall runs out of memory, and can no
longer instantiate the state required to pass legitimate flows.
Other possible DDoS attacks are discussed in [RFC4732].
In each of the cases described above, the possible arrangements
between the DOTS client and DOTS server to mitigate the attack are
discussed in [I-D.ietf-dots-use-cases]. An example of network
diagram showing a deployment of these elements is shown in Figure 1.
Architectural relationships between involved DOTS agents is explained
in [I-D.ietf-dots-architecture]. In this example, the DOTS server is
operating on the access network.
Network
Resource CPE router Access network __________
+-----------+ +--------------+ +-------------+ / \
| |____| |_______| |___ | Internet |
|DOTS client| | DOTS gateway | | DOTS server | | |
| | | | | | | |
+-----------+ +--------------+ +-------------+ \__________/
Figure 1
The DOTS server can also be running on the Internet, as depicted in
Figure 2.
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Network DDoS mitigation
Resource CPE router __________ service
+-----------+ +-------------+ / \ +-------------+
| |____| |_______| |___ | |
|DOTS client| |DOTS gateway | | Internet | | DOTS server |
| | | | | | | | |
+-----------+ +-------------+ \__________/ +-------------+
Figure 2
In typical deployments, the DOTS client belongs to a different
administrative domain than the DOTS server. For example, the DOTS
client is a web server serving content owned and operated by an
domain, while the DOTS server is owned and operated by a different
domain providing DDoS mitigation services. That domain providing
DDoS mitigation service might, or might not, also provide Internet
access service to the website operator.
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 the DOTS server or
indirectly via a DOTS gateway.
This document focuses on the DOTS signal channel.
4. Happy Eyeballs for DOTS Signal Channel
DOTS signaling can happen with DTLS [RFC6347] over UDP and TLS
[RFC5246] over TCP. A DOTS client can use DNS to determine the IP
address(es) of a DOTS server or a DOTS client may be provided with
the list of DOTS server IP addresses. The DOTS client MUST know a
DOTS server's domain name; hard-coding the domain name of the DOTS
server into software is NOT RECOMMENDED in case the domain name is
not valid or needs to change for legal or other reasons. The DOTS
client performs A and/or AAAA record lookup of the domain name and
the result will be a list of IP addresses, each of which can be used
to contact the DOTS server using UDP and TCP.
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 can
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, the DOTS
client will fail to establish a DTLS session with the DOTS server and
will, then, have to fall back to TLS over TCP incurring significant
connection delays. [I-D.ietf-dots-requirements] discusses that DOTS
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client and server will have to support both connectionless and
connection-oriented protocols.
To overcome these connection setup problems, the DOTS client can try
connecting to the DOTS server using both IPv6 and IPv4, and try both
DTLS over UDP and TLS over TCP in a fashion similar to the Happy
Eyeballs mechanism [RFC6555]. These connection attempts are
performed by the DOTS client when its initializes, and the client
uses that information for its subsequent alert to the DOTS server.
In order of preference (most preferred first), it is UDP over IPv6,
UDP over IPv4, TCP over IPv6, and finally TCP over IPv4, which
adheres to address preference order [RFC6724] and the DOTS preference
that UDP be used over TCP (to avoid TCP's head of line blocking).
DOTS client DOTS server
| |
|--DTLS ClientHello, IPv6 ---->X |
|--TCP SYN, IPv6-------------->X |
|--DTLS ClientHello, IPv4 ---->X |
|--TCP SYN, IPv4----------------------------------------->|
|--DTLS ClientHello, IPv6 ---->X |
|--TCP SYN, IPv6-------------->X |
|<-TCP SYNACK---------------------------------------------|
|--DTLS ClientHello, IPv4 ---->X |
|--TCP ACK----------------------------------------------->|
|<------------Establish TLS Session---------------------->|
|----------------DOTS signal----------------------------->|
| |
Figure 3: Happy Eyeballs
In reference to Figure 3, 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 is
dropped by a middle box but has little impact to the DOTS client
because there is no long delay before using IPv4 and TCP. The IPv6
path and UDP over IPv6 and IPv4 is retried until the DOTS client
gives up.
5. DOTS Signal Channel
5.1. Overview
Constrained Application Protocol (CoAP) [RFC7252] is used for DOTS
signal channel (Figure 4). COAP was designed according to the REST
architecture, and thus exhibits functionality similar to that of
HTTP, it is quite straightforward to map from CoAP to HTTP and from
HTTP to CoAP. CoAP has been defined to make use of both DTLS over
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UDP and TLS over TCP [I-D.ietf-core-coap-tcp-tls]. The advantages of
COAP are: (1) Like HTTP, CoAP is based on the successful REST model,
(2) CoAP is designed to use minimal resources, (3) CoAP integrates
with JSON, CBOR or any other data format, (4) asynchronous message
exchanges, (5) includes a congestion control mechanism (6) allows
configuration of message transmission parameters specific to the
application environment (including dynamically adjusted values, see
Section 4.8.1 in [RFC7252]) etc.
+--------------+
| DOTS |
+--------------+
| CoAP |
+--------------+
| TLS | DTLS |
+--------------+
| TCP | UDP |
+--------------+
| IP |
+--------------+
Figure 4: Abstract Layering of DOTS signal channel over CoAP over
(D)TLS
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 client SHOULD re-use the (D)TLS session.
Concise Binary Object Representation (CBOR) [RFC7049] is a binary
encoding designed for small code and message size, CBOR encoded
payloads are used to convey signal channel specific payload messages
that convey request parameters and response information such as
errors. This specification uses the encoding rules defined in
[I-D.ietf-core-yang-cbor] for representing DOTS signal channel
configuration data defined using YANG (Section 5.2) as CBOR data.
5.2. DOTS Signal YANG Model
5.2.1. Mitigation Request Model structure
This document defines the YANG module "ietf-dots-signal", which has
the following structure:
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module: ietf-dots-signal
+--rw mitigation-scope
+--rw scope* [policy-id]
+--rw policy-id int32
+--rw target-ip* inet:ip-address
+--rw target-prefix* inet:ip-prefix
+--rw target-port-range* [lower-port upper-port]
| +--rw lower-port inet:port-number
| +--rw upper-port inet:port-number
+--rw target-protocol* uint8
+--rw FQDN* inet:domain-name
+--rw URI* inet:uri
+--rw E.164* string
+--rw alias* string
+--rw lifetime? int32
5.2.2. Mitigation Request Model
<CODE BEGINS> file "ietf-dots-signal@2016-11-28.yang"
module ietf-dots-signal {
namespace "urn:ietf:params:xml:ns:yang:ietf-dots-signal";
prefix "signal";
import ietf-inet-types {
prefix "inet";
}
organization "Cisco Systems, Inc.";
contact "Tirumaleswar Reddy <tireddy@cisco.com>";
description
"This module contains YANG definition for DOTS
signal sent by the DOTS client to the DOTS server";
revision 2016-11-28 {
reference
"https://tools.ietf.org/html/draft-reddy-dots-signal-channel";
}
container mitigation-scope {
description "top level container for mitigation request";
list scope {
key policy-id;
description "Identifier for the mitigation request";
leaf policy-id {
type int32;
description "policy identifier";
}
leaf-list target-ip {
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type inet:ip-address;
description "IP address";
}
leaf-list target-prefix {
type inet:ip-prefix;
description "prefix";
}
list target-port-range {
key "lower-port upper-port";
description "Port range. When only lower-port is present,
it represents a single port.";
leaf lower-port {
type inet:port-number;
mandatory true;
description "lower port";
}
leaf upper-port {
type inet:port-number;
must ". >= ../lower-port" {
error-message
"The upper-port must be greater than or
equal to lower-port";
}
description "upper port";
}
}
leaf-list target-protocol {
type uint8;
description "Internet Protocol number";
}
leaf-list FQDN {
type inet:domain-name;
description "FQDN";
}
leaf-list URI {
type inet:uri;
description "URI";
}
leaf-list E.164 {
type string;
description "E.164 number";
}
leaf-list alias {
type string;
description "alias name";
}
leaf lifetime {
type int32;
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description "lifetime";
}
}
}
}
<CODE ENDS>
5.2.3. Session Configuration Model structure
This document defines the YANG module "ietf-dots-signal-config",
which has the following structure:
module: ietf-dots-signal-config
+--rw signal-config
+--rw policy-id? int32
+--rw heartbeat-interval? int16
+--rw max-retransmit? int16
+--rw ack-timeout? int16
+--rw ack-random-factor? decimal64
5.2.4. Session Configuration Model
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<CODE BEGINS> file "ietf-dots-signal-config@2016-11-28.yang"
module ietf-dots-signal-config {
namespace "urn:ietf:params:xml:ns:yang:ietf-dots-signal-config";
prefix "config";
organization "Cisco Systems, Inc.";
contact "Tirumaleswar Reddy <tireddy@cisco.com>";
description
"This module contains YANG definition for DOTS
signal channel session configuration";
revision 2016-11-28 {
reference
"https://tools.ietf.org/html/draft-reddy-dots-signal-channel";
}
container signal-config {
description "top level container for DOTS signal channel session
configuration";
leaf policy-id {
type int32;
description "Identifier for the DOTS signal channel
session configuration data";
}
leaf heartbeat-interval {
type int16;
description "heartbeat interval";
}
leaf max-retransmit {
type int16;
description "Maximum number of retransmissions";
}
leaf ack-timeout {
type int16;
description "Initial retransmission timeout value";
}
leaf ack-random-factor {
type decimal64 {
fraction-digits 2;
}
description "Random factor used to influence the timing of
retransmissions";
}
}
}
<CODE ENDS>
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5.3. Mitigation Request
The following APIs define the means to convey a DOTS signal from a
DOTS client to a DOTS server:
PUT requests: are used to convey the DOTS signal from a DOTS client
to a DOTS server over the signal channel, possibly traversing a
DOTS gateway, indicating the DOTS client's need for mitigation, as
well as the scope of any requested mitigation (Section 5.3.1).
DOTS gateway act as a CoAP-to-CoAP Proxy (explained in [RFC7252]).
PUT requests are also used by the DOTS client to convey mitigation
efficacy updates to the DOTS server (Section 5.3.4).
DELETE requests: are used by the DOTS client to withdraw the request
for mitigation from the DOTS server (Section 5.3.2).
GET requests: are used by the DOTS client to retrieve the DOTS
signal(s) it had conveyed to the DOTS server (Section 5.3.3).
Reliability is provided to the requests and responses by marking them
as Confirmable (CON) messages. As explained in Section 2.1 of
[RFC7252], 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 [RFC7252]. Reliability is
provided to the responses by marking them as Confirmable (CON)
messages. The DOTS server can either piggyback the response in the
acknowledgement message or if the DOTS server is not able to 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 [RFC7252]. When the response
is ready, the server sends it in a new Confirmable message which then
in turn needs to be acknowledged by the DOTS client (see Sections
5.2.1 and Sections 5.2.2 in [RFC7252]).
DOTS agents should follow the data transmission guidelines discussed
in Section 3.1.3 of [I-D.ietf-tsvwg-rfc5405bis] and control
transmission behavior by not sending on average more than one UDP
datagram per RTT to the peer DOTS agent. Requests marked by the DOTS
client as Non-confirmable messages are sent at regular intervals
until a response is received from the DOTS server and if the DOTS
client cannot maintain a RTT estimate then it SHOULD NOT send more
than one Non-confirmable request every 3 seconds, and SHOULD use an
even less aggressive rate when possible (case 2 in Section 3.1.3 of
[I-D.ietf-tsvwg-rfc5405bis]).
Implementation Note: A DOTS client that receives a response in a CON
message may want to clean up the message state right after sending
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the ACK. If that ACK is lost and the DOTS server retransmits the
CON, the DOTS client may no longer have any state to which to
correlate this response, making the retransmission an unexpected
message; 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 in [RFC7252] for more
details).
5.3.1. Convey DOTS Signals
When suffering an attack and desiring DoS/DDoS mitigation, a DOTS
signal is sent by the DOTS client to the DOTS server. A PUT request
is used to convey a DOTS signal to the DOTS server (Figure 5,
illustrated in JSON diagnostic notation). The DOTS server can enable
mitigation on behalf of the DOTS client by communicating the DOTS
client's request to the mitigator and relaying any mitigator feedback
to the requesting DOTS client. The PUT request and response are
marked as Non-confirmable messages.
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Header: PUT (Code=0.03)
Uri-Host: "host"
Uri-Path: ".well-known"
Uri-Path: "version"
Uri-Path: "dots-signal"
Uri-Path: "signal"
Content-Type: "application/cbor"
{
"mitigation-scope": {
"scope": [
{
"policy-id": integer,
"target-ip": [
"string"
],
"target-prefix": [
"string"
],
"target-port-range": [
{
"lower-port": integer,
"upper-port": integer
}
],
"target-protocol": [
integer
],
"FQDN": [
"string"
],
"URI": [
"string"
],
"E.164": [
"string"
],
"alias": [
"string"
],
"lifetime": integer
}
]
}
}
Figure 5: PUT to convey DOTS signals
The parameters are described below.
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policy-id: Identifier for the mitigation request represented using
an integer. This identifier MUST be unique for each mitigation
request bound to the DOTS client, i.e., the policy-id parameter
value in the mitigation request needs to be unique relative to the
policy-id parameter values of active mitigation requests conveyed
from the DOTS client to the DOTS server. This identifier MUST be
generated by the DOTS client. This document does not make any
assumption about how this identifier is generated. This is a
mandatory attribute.
target-ip: A list of IP addresses under attack. IP addresses are
separated by commas. This is an optional attribute.
target-prefix: A list of prefixes under attack. Prefixes are
separated by commas. Prefixes are represented using CIDR notation
[RFC4632]. This is an optional attribute.
target-port-range: A list of ports under attack. The port range,
lower-port for lower port number and upper-port for upper port
number. When only lower-port is present, it represents a single
port. For TCP, UDP, SCTP, or DCCP: the range of ports (e.g.,
1024-65535). This is an optional attribute.
target-protocol: A list of protocols under attack. Internet
Protocol numbers. This is an optional attribute.
FQDN: A list of Fully Qualified Domain Names. Fully Qualified
Domain Name (FQDN) is the full name of a system, rather than just
its hostname. For example, "venera" is a hostname, and
"venera.isi.edu" is an FQDN. This is an optional attribute.
URI: A list of Uniform Resource Identifiers (URI). This is an
optional attribute.
E.164: A list of E.164 numbers. This is an optional attribute.
alias: A list of aliases (see Section 3.1.1 in
[I-D.reddy-dots-data-channel]). This is an optional attribute.
lifetime: Lifetime of the mitigation request in seconds. 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. The default lifetime of the
mitigation request is 3600 seconds (60 minutes) -- 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. A lifetime of
zero indicates indefinite lifetime for the mitigation request.
The server MUST always indicate the actual lifetime in the
response. This is an optional attribute in the request.
The CBOR key values for the parameters are defined in Section 6. The
IANA Considerations section defines how the CBOR key values can be
allocated to standards bodies and vendors. In the PUT request at
least one of the attributes target-ip or target-prefix or FQDN or URI
or alias MUST be present. DOTS agents can safely ignore Vendor-
Specific parameters they don't understand. The relative order of two
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mitigation requests from a DOTS client is determined by comparing
their respective policy-id values. The mitigation request with
higher numeric policy-id value has higher precedence (and thus will
match before) than the mitigation request with lower numeric policy-
id value.
In both DOTS signal and data channel sessions, the DOTS client MUST
authenticate itself to the DOTS server (Section 9). The DOTS server
couples the DOTS signal and data channel sessions using the DOTS
client identity, 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 then the DOTS server returns 4.00 (Bad
Request) in the response. The DOTS server couples the DOTS signal
channel sessions using the DOTS client identity, the DOTS server uses
policy-id parameter value to detect duplicate mitigation requests.
Figure 6 shows a PUT request example to signal that ports 80, 8080,
and 443 on the servers 2002:db8:6401::1 and 2002:db8:6401::2 are
being attacked (illustrated in JSON diagnostic notation).
Header: PUT (Code=0.03)
Uri-Host: "www.example.com"
Uri-Path: ".well-known"
Uri-Path: "v1"
Uri-Path: "dots-signal"
Uri-Path: "signal"
Content-Format: "application/cbor"
{
"mitigation-scope": {
"scope": [
{
"policy-id": 12332,
"target-ip": [
"2002:db8:6401::1",
"2002:db8:6401::2"
],
"target-port-range": [
{
"lower-port": 80
},
{
"lower-port": 443
},
{
"lower-port": 8080
}
],
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"target-protocol": [
6
]
}
]
}
}
The CBOR encoding format is shown below:
a1 # map(1)
01 # unsigned(1)
a1 # map(1)
02 # unsigned(2)
81 # array(1)
a4 # map(4)
03 # unsigned(3)
19 302c # unsigned(12332)
04 # unsigned(4)
82 # array(2)
70 # text(16)
323030323a6462383a363430313a3a31 # "2002:db8:6401::1"
70 # text(16)
323030323a6462383a363430313a3a32 # "2002:db8:6401::2"
05 # unsigned(5)
83 # array(3)
a1 # map(1)
06 # unsigned(6)
18 50 # unsigned(80)
a1 # map(1)
06 # unsigned(6)
19 01bb # unsigned(443)
a1 # map(1)
06 # unsigned(6)
19 1f90 # unsigned(8080)
08 # unsigned(8)
81 # array(1)
06 # unsigned(6)
Figure 6: POST for DOTS signal
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. 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
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DOTS client. If the DOTS server does not find the policy-id
parameter value conveyed in the PUT request in its configuration data
then the server MAY accept the mitigation request, and a 2.01
(Created) response is returned to the DOTS client, and the DOTS
server will try to mitigate the attack. If the DOTS server finds the
policy-id parameter value conveyed in the PUT request in its
configuration data then the server MAY update the mitigation request,
and a 2.04 (Changed) response is returned to indicate a successful
updation of the mitigation request. If the request is missing one or
more mandatory attributes, then 4.00 (Bad Request) will be returned
in the response or if the request contains invalid or unknown
parameters then 4.02 (Invalid query) will be returned in the
response. For responses indicating a client or server error, the
payload explains the error situation of the result of the requested
action (Section 5.5 in [RFC7252]).
5.3.2. Withdraw a DOTS Signal
A DELETE request is used to withdraw a DOTS signal from a DOTS server
(Figure 7). The DELETE request and response are marked as
Confirmable messages.
Header: DELETE (Code=0.04)
Uri-Host: "host"
Uri-Path: ".well-known"
Uri-Path: "version"
Uri-Path: "dots-signal"
Uri-Path: "signal"
Content-Format: "application/cbor"
{
"mitigation-scope": {
"scope": [
{
"policy-id": integer
}
]
}
}
Figure 7: Withdraw DOTS signal
If the DOTS server does not find the policy-id parameter value
conveyed in the DELETE request in its configuration data, then it
responds with a 4.04 (Not Found) error response code. The DOTS
server successfully acknowledges a DOTS client's request to withdraw
the DOTS signal using 2.02 (Deleted) response code, and ceases
mitigation activity as quickly as possible.
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5.3.3. Retrieving a DOTS Signal
A GET request is used to retrieve information and status of a DOTS
signal from a DOTS server (Figure 8). If the DOTS server does not
find the policy-id parameter value conveyed in the GET request in its
configuration data, then it responds with a 4.04 (Not Found) error
response code. The GET request is marked as Non-confirmable message.
The 'c' (content) parameter and its permitted values defined in
[I-D.ietf-core-comi] can be used to retreive non-configuration data
or configuration data or both.
1) To retrieve all DOTS signals signaled by the DOTS client.
Header: GET (Code=0.01)
Uri-Host: "host"
Uri-Path: ".well-known"
Uri-Path: "version"
Uri-Path: "dots-signal"
Uri-Path: "signal"
Observe : 0
2) To retrieve a specific DOTS signal signaled by the DOTS client.
The configuration data in the response will be formatted in the
same order it was processed at the DOTS server.
Header: GET (Code=0.01)
Uri-Host: "host"
Uri-Path: ".well-known"
Uri-Path: "version"
Uri-Path: "dots-signal"
Uri-Path: "signal"
Observe : 0
Content-Format: "application/cbor"
{
"mitigation-scope": {
"scope": [
{
"policy-id": integer
}
]
}
}
Figure 8: GET to retrieve the rules
Figure 9 shows a response example of all the active mitigation
requests associated with the DOTS client on the DOTS server and the
mitigation status of each mitigation request.
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{
"mitigation-scope":[
{
"scope": [
{
"policy-id": 12332,
"target-protocol": [
17
],
"lifetime":1800,
"status":2,
"bytes_dropped": 134334555,
"bps_dropped": 43344,
"pkts_dropped": 333334444,
"pps_dropped": 432432
}
]
},
{
"scope": [
{
"policy-id": 12333,
"target-protocol": [
6
],
"lifetime":1800,
"status":3
"bytes_dropped": 0,
"bps_dropped": 0,
"pkts_dropped": 0,
"pps_dropped": 0
}
]
}
]
}
Figure 9: Response body
The mitigation status parameters are described below.
bytes_dropped: The total dropped byte count for the mitigation
request. This is a optional attribute.
bps_dropped: The average dropped bytes per second for the mitigation
request. This is a optional attribute.
pkts_dropped: The total dropped packet count for the mitigation
request. This is a optional attribute.
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pps_dropped: The average dropped packets per second for the
mitigation request. This is a optional attribute.
status: Status of attack mitigation. The 'status' parameter is a
mandatory attribute.
The various possible values of 'status' parameter are explained
below:
/--------------------+---------------------------------------------------\
| Parameter value | Description |
|--------------------+---------------------------------------------------|
| 1 | Attack mitigation is in progress |
| | (e.g., changing the network path to re-route the |
| | inbound traffic to DOTS mitigator). |
+------------------------------------------------------------------------+
| 2 | Attack is successfully mitigated |
| | (e.g., traffic is redirected to a DDOS mitigator |
| | and attack traffic is dropped). |
+------------------------------------------------------------------------+
| 3 | Attack has stopped and the DOTS client |
| | can withdraw the mitigation request. |
+------------------------------------------------------------------------+
| 4 | Attack has exceeded the mitigation provider |
| | capability. |
\--------------------+---------------------------------------------------/
The observe option defined in [RFC7641] extends the CoAP core
protocol with a mechanism for a CoAP client to "observe" a resource
on a CoAP server: the client retrieves a representation of the
resource and requests this representation be updated by the server as
long as the client is interested in the resource. 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 notifications within the bidirectional signal
channel allows unsolicited message delivery, enabling asynchronous
notifications between the agents. A DOTS client that is no longer
interested in receiving notifications from the DOTS server can simply
"forget" the observation. The notification response is marked as
Non-confirmable message. When the DOTS server then 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.
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DOTS Client DOTS Server
| |
| GET /<policy-id number> |
| Token: 0x4a | Registration
| Observe: 0 |
+-------------------------->|
| |
| 2.05 Content |
| Token: 0x4a | Notification of
| Observe: 12 | the current state
| status: "mitigation |
| in progress" |
|<--------------------------+
| 2.05 Content |
| Token: 0x4a | Notification upon
| Observe: 44 | a state change
| status: "mitigation |
| complete" |
|<--------------------------+
| 2.05 Content |
| Token: 0x4a | Notification upon
| Observe: 60 | a state change
| status: "attack stopped" |
|<--------------------------+
| |
Figure 10: Notifications of attack mitigation status
5.3.3.1. Mitigation Status
A DOTS client retrieves the information about a DOTS signal at
frequent intervals to determine the status of an attack. 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, and the
DOTS client recalls the mitigation request.
A DOTS client should react to the status of the attack from the DOTS
server and not the fact that it has recognized, using its own means,
that the attack has been mitigated. This ensures that the DOTS
client does not recall a mitigation request in a premature fashion
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 and the attack is not completely averted.
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5.3.4. Efficacy Update from DOTS Client
While DDoS mitigation is active, a DOTS client MAY frequently
transmit DOTS mitigation efficacy updates to the relevant DOTS
server. An PUT request (Figure 11) is used to convey the mitigation
efficacy update to the DOTS server. The PUT request MUST include all
the parameters used in the PUT request to convey the DOTS signal
(Section 5.3.1). The PUT request and response are marked as Non-
Confirmable messages.
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Header: PUT (Code=0.03)
Uri-Host: "host"
Uri-Path: ".well-known"
Uri-Path: "version"
Uri-Path: "dots-signal"
Uri-Path: "signal"
Content-Format: "application/cbor"
{
"mitigation-scope": {
"scope": [
{
"policy-id": integer,
"target-ip": [
"string"
],
"target-port-range": [
{
"lower-port": integer,
"upper-port": integer
}
],
"target-protocol": [
integer
],
"FQDN": [
"string"
],
"URI": [
"string"
],
"E.164": [
"string"
],
"alias": [
"string"
],
"lifetime": integer,
"attack-status": integer
}
]
}
}
Figure 11: Efficacy Update
The 'attack-status' parameter is a mandatory attribute. The various
possible values contained in the 'attack-status' parameter are
explained below:
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/--------------------+------------------------------------------------------\
| Parameter value | Description |
|--------------------+------------------------------------------------------|
| 1 | DOTS client determines that it is still under attack.|
+---------------------------------------------------------------------------+
| 2 | DOTS client determines that the attack is |
| | successfully mitigated |
| | (e.g., attack traffic is not seen). |
\--------------------+------------------------------------------------------/
The DOTS server indicates the result of processing the PUT request
using CoAP response codes. The response code 2.04 (Changed) will be
returned in the response if the DOTS server has accepted the
mitigation efficacy update. If the DOTS server does not find the
policy-id parameter value conveyed in the PUT request in its
configuration data then the server MAY accept the mitigation request
and will try to mitigate the attack, resulting in a 2.01 (Created)
Response Code. The 5.xx response codes are returned if the DOTS
server has erred or is incapable of performing the mitigation.
5.4. DOTS Signal Channel Session Configuration
The DOTS client can negotiate, configure and retrieve the DOTS signal
channel session behavior. The DOTS signal channel can be used, for
example, to configure the following:
a. Heartbeat interval: DOTS agents regularly send heartbeats to each
other after mutual authentication in order to keep the DOTS
signal channel open.
b. Acceptable signal loss ratio: Maximum retransmissions,
retransmission timeout value and other message transmission
parameters for the DOTS signal channel.
5.4.1. Discover Acceptable Configuration Parameters
A GET request is used to obtain acceptable configuration parameters
on the DOTS server for DOTS signal channel session configuration.
Figure 12 shows how to obtain acceptable configuration parameters for
the server. The GET request and response are marked as Confirmable
messages.
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Header: GET (Code=0.01)
Uri-Host: "host"
Uri-Path: ".well-known"
Uri-Path: "version"
Uri-Path: "dots-signal"
Uri-Path: "config"
Figure 12: GET to retrieve configuration
The DOTS server in the 2.05 (Content) response conveys the minimum
and maximum attribute values acceptable by the DOTS server.
Content-Format: "application/cbor"
{
"heartbeat-interval": {"MinValue": integer, "MaxValue" : integer},
"max-retransmit": {"MinValue": integer, "MaxValue" : integer},
"ack-timeout": {"MinValue": integer, "MaxValue" : integer},
"ack-random-factor": {"MinValue": number, "MaxValue" : number}
}
Figure 13: GET response body
5.4.2. Convey DOTS Signal Channel Session Configuration
A POST request is used to convey the configuration parameters for the
signaling channel (e.g., heartbeat interval, maximum retransmissions
etc). Message transmission parameters for CoAP are defined in
Section 4.8 of [RFC7252]. If the DOTS agent wishes to change the
default values of message transmission parameters then it should
follow the guidence given in Section 4.8.1 of [RFC7252]. The DOTS
agents MUST use the negotiated values for message transmission
parameters and default values for non-negotiated message transmission
parameters. The signaling channel session configuration is
applicable to a single DOTS signal channel session between the DOTS
agents. The POST request and response are marked as Confirmable
messages.
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Header: POST (Code=0.02)
Uri-Host: "host"
Uri-Path: ".well-known"
Uri-Path: "version"
Uri-Path: "dots-signal"
Uri-Path: "config"
Content-Format: "application/cbor"
{
"signal-config": {
"policy-id": integer,
"heartbeat-interval": integer,
"max-retransmit": integer,
"ack-timeout": integer,
"ack-random-factor": number
}
}
Figure 14: POST to convey the DOTS signal channel session
configuration data.
The parameters are described below:
policy-id: Identifier for the DOTS signal channel session
configuration data represented as an integer. This identifier
MUST be generated by the DOTS client. This document does not make
any assumption about how this identifier is generated. This is a
mandatory attribute.
heartbeat-interval: Heartbeat interval to check the DOTS peer
health. This is an optional attribute.
max-retransmit: Maximum number of retransmissions for a message
(referred to as MAX_RETRANSMIT parameter in CoAP). This is an
optional attribute.
ack-timeout: Timeout value in seconds used to calculate the intial
retransmission timeout value (referred to as ACK_TIMEOUT parameter
in CoAP). This is an optional attribute.
ack-random-factor: Random factor used to influence the timing of
retransmissions (referred to as ACK_RANDOM_FACTOR parameter in
CoAP). This is an optional attribute.
In the POST request at least one of the attributes heartbeat-interval
or max-retransmit or ack-timeout or ack-random-factor MUST be
present. The POST request with higher numeric policy-id value over-
rides the DOTS signal channel session configuration data installed by
a POST request with a lower numeric policy-id value.
Figure 15 shows a POST request example to convey the configuration
parameters for the DOTS signal channel.
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Header: POST (Code=0.02)
Uri-Host: "www.example.com"
Uri-Path: ".well-known"
Uri-Path: "v1"
Uri-Path: "dots-signal"
Uri-Path: "config"
Content-Format: "application/cbor"
{
"signal-config": {
"policy-id": 1234534333242,
"heartbeat-interval": 30,
"max-retransmit": 7,
"ack-timeout": 5,
"ack-random-factor": 1.5
}
}
Figure 15: POST to convey the configuration parameters
The DOTS server indicates the result of processing the POST request
using CoAP response codes. The CoAP response will include the CBOR
body received in the request. Response code 2.01 (Created) will be
returned in the response if the DOTS server has accepted the
configuration parameters. If the request is missing one or more
mandatory attributes then 4.00 (Bad Request) will be returned in the
response or if the request contains invalid or unknown parameters
then 4.02 (Invalid query) will be returned in the response. Response
code 4.22 (Unprocessable Entity) will be returned in the response if
any of the heartbeat-interval, max-retransmit, target-protocol, ack-
timeout and ack-random-factor attribute values is not acceptable to
the DOTS server. The DOTS server in the error response conveys the
minumum and maximum attribute values acceptable by the DOTS server.
The DOTS client can re-try and send the POST request with updated
attribute values acceptable to the DOTS server.
Content-Format: "application/cbor"
{
"heartbeat-interval": {"MinValue": 15, "MaxValue" : 60},
"max-retransmit": {"MinValue": 3, "MaxValue" : 15},
"ack-timeout": {"MinValue": 1, "MaxValue" : 30},
"ack-random-factor": {"MinValue": 1.0, "MaxValue" : 4.0}
}
Figure 16: Error response body
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5.4.3. Delete DOTS Signal Channel Session Configuration
A DELETE request is used to delete the installed DOTS signal channel
session configuration data (Figure 17). The DELETE request and
response are marked as Confirmable messages.
Header: DELETE (Code=0.04)
Uri-Host: "host"
Uri-Path: ".well-known"
Uri-Path: "version"
Uri-Path: "dots-signal"
Uri-Path: "config"
Content-Format: "application/cbor"
{
"signal-config": {
"policy-id": integer
}
}
Figure 17: DELETE configuration
If the DOTS server does not find the policy-id parameter value
conveyed in the DELETE request in its configuration data, then it
responds with a 4.04 (Not Found) error response code. The DOTS
server successfully acknowledges a DOTS client's request to remove
the DOTS signal channel session configuration using 2.02 (Deleted)
response code.
5.4.4. Retrieving DOTS Signal Channel Session Configuration
A GET request is used to retrieve the installed DOTS signal channel
session configuration data from a DOTS server. Figure 18 shows how
to retrieve the DOTS signal channel session configuration data. The
GET request and response are marked as Confirmable messages.
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Header: GET (Code=0.01)
Uri-Host: "host"
Uri-Path: ".well-known"
Uri-Path: "version"
Uri-Path: "dots-signal"
Uri-Path: "config"
Content-Format: "application/cbor"
{
"signal-config": {
"policy-id": integer
}
}
Figure 18: GET to retrieve configuration
5.5. Redirected Signaling
Redirected Signaling is discussed in detail in Section 3.2.2 of
[I-D.ietf-dots-architecture]. If the DOTS server wants to redirect
the DOTS client to an alternative DOTS server for a signaling session
then the response code 3.00 (alternate server) will be returned in
the response to the client. The DOTS server can return the error
response code 3.00 in response to a POST or PUT request from the DOTS
client or convey the error response code 3.00 in a unidirectional
notification response from the DOTS server. The DOTS server can mark
the notification response conveying the alternate server address as a
a Confirmable message to request an acknowledgement from the DOTS
client.
The DOTS server in the error response conveys the alternate DOTS
server FQDN, and the alternate DOTS server IP addresses and TTL (time
to live) values in the CBOR body.
{
"alt-server": "string",
"alt-server-record": [
{
"addr": "string",
"TTL" : integer,
}
]
}
Figure 19: Error response body
The parameters are described below:
alt-server: FQDN of alternate DOTS server.
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addr: IP address of alternate DOTS server.
TTL: Time to live represented as an integer number of seconds.
Figure 20 shows a 3.00 response example to convey the DOTS alternate
server www.example-alt.com, its IP addresses 2002:db8:6401::1 and
2002:db8:6401::2, and TTL values 3600 and 1800.
{
"alt-server": "www.example-alt.com",
"alt-server-record": [
{
"TTL" : 3600,
"addr": "2002:db8:6401::1"
},
{
"TTL" : 1800,
"addr": "2002:db8:6401::2"
}
]
}
Figure 20: Example of error response body
When the DOTS client receives 3.00 response, it considers the current
request as having failed, but SHOULD try the request with the
alternate DOTS server. During a DDOS attack, the DNS server may be
subjected to DDOS attack, alternate DOTS server IP addresses conveyed
in the 3.00 response help the DOTS client to skip DNS lookup of the
alternate DOTS server and can try to establish UDP or TCP session
with the alternate DOTS server IP addresses. The DOTS client SHOULD
implement DNS64 function to handle the scenario where IPv6-only DOTS
client communicates with IPv4-only alternate DOTS server.
5.6. Heartbeat Mechanism
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 alive
firewall or NAT bindings. This probing reduces the frequency of
needing a new handshake when a DOTS signal needs to be conveyed to
the DOTS server. In DOTS over UDP, heartbeat messages can be
exchanged between the DOTS agents using the "COAP ping" mechanism
(Section 4.2 in [RFC7252]). The DOTS agent sends an Empty
Confirmable message and the peer DOTS agent will respond by sending
an Reset message. In DOTS over TCP, heartbeat messages can be
exchanged between the DOTS agents using the Ping and Pong messages
(Section 4.4 in [I-D.ietf-core-coap-tcp-tls]). The DOTS agent sends
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an Ping message and the peer DOTS agent will respond by sending an
single Pong message.
6. Mapping parameters to CBOR
All parameters in DOTS signal channel are mapped to CBOR types as
follows and are given an integer key value to save space.
/--------------------+------------------------+--------------------------\
| Parameter name | CBOR key | CBOR major type of value |
|--------------------+------------------------+--------------------------|
| mitigation-scope | 1 | 5 (map) |
| scope | 2 | 5 (map) |
| policy-id | 3 | 0 (unsigned) |
| target-ip | 4 | 4 (array) |
| target-port-range | 5 | 4 |
| lower-port | 6 | 0 |
| upper-port | 7 | 0 |
| target-protocol | 8 | 4 |
| FQDN | 9 | 4 |
| URI | 10 | 4 |
| E.164 | 11 | 4 |
| alias | 12 | 4 |
| lifetime | 13 | 0 |
| attack-status | 14 | 0 |
| signal-config | 15 | 5 |
| heartbeat-interval | 16 | 0 |
| max-retransmit | 17 | 0 |
| ack-timeout | 18 | 0 |
| ack-random-factor | 19 | 7 |
| MinValue | 20 | 0 |
| MaxValue | 21 | 0 |
| status | 22 | 0 |
| bytes_dropped | 23 | 0 |
| bps_dropped | 24 | 0 |
| pkts_dropped | 25 | 0 |
| pps_dropped | 26 | 0 |
\--------------------+------------------------+--------------------------/
Figure 21: CBOR mappings used in DOTS signal channel message
7. (D)TLS Protocol Profile and Performance considerations
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 machine-in-the-middle and
protocol downgrade. These are general attacks on (D)TLS and not
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specific to DOTS over (D)TLS; please refer to the (D)TLS RFCs for
discussion of these security issues. DOTS agents MUST adhere to the
(D)TLS implementation recommendations and security considerations of
[RFC7525] except with respect to (D)TLS version. Since encryption of
DOTS using (D)TLS is virtually a green-field deployment DOTS agents
MUST implement only (D)TLS 1.2 or later.
Implementations compliant with this profile MUST implement all of the
following items:
o DOTS agents MUST support DTLS record replay detection (Section 3.3
in [RFC6347]) to protect against replay attacks.
o DOTS client can use (D)TLS session resumption without server-side
state [RFC5077] to resume session and convey the DOTS signal.
o Raw public keys [RFC7250] which reduce the size of the
ServerHello, and can be used by servers that cannot obtain
certificates (e.g., DOTS gateways on private networks).
Implementations compliant with this profile SHOULD implement all of
the following items to reduce the delay required to deliver a DOTS
signal:
o TLS False Start [RFC7918] which reduces round-trips by allowing
the TLS second flight of messages (ChangeCipherSpec) to also
contain the DOTS signal.
o Cached Information Extension [RFC7924] which avoids transmitting
the server's certificate and certificate chain if the client has
cached that information from a previous TLS handshake.
o TCP Fast Open [RFC7413] can reduce the number of round-trips to
convey DOTS signal.
7.1. MTU and Fragmentation Issues
To avoid DOTS signal message fragmentation and the consequently
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. The length of the URL MUST NOT exceed 256 bytes. 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 [RFC6347]]. 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-ip' parameter could be
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split into multiple lists and each list conveyed in a new POST
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 absolutely ensure that there is no IP
fragmentation. If IPv4 support on unusual networks is a
consideration and path MTU is unknown, implementations may want to
limit themselves to more conservative IPv4 datagram sizes such as 576
bytes, as per [RFC0791] IP packets up to 576 bytes should never need
to be fragmented, thus sending a maximum of 500 bytes of DOTS signal
over a UDP datagram will generally avoid IP fragmentation.
8. (D)TLS 1.3 considerations
TLS 1.3 [I-D.ietf-tls-tls13] provides critical latency improvements
for connection establishment over TLS 1.2. The DTLS 1.3 protocol
[I-D.rescorla-tls-dtls13] is based on the TLS 1.3 protocol and
provides equivalent security guarantees. (D)TLS 1.3 provides two
basic handshake modes of interest to DOTS signal channel:
o Absent packet loss, a full handshake in which the DOTS client is
able to send the DOTS signal message after one round trip and the
DOTS server immediately after receiving the first DOTS signal
message from the client.
o 0-RTT mode in which the DOTS client can authenticate itself and
send DOTS signal message on its first flight, 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 SHOULD
establish a (D)TLS session with the DOTS server during peacetime
and share a PSK. During DDOS attack, the DOTS client can use the
(D)TLS session to convey the DOTS signal message and if there is
no response from the server after multiple re-tries then the DOTS
client can resume the (D)TLS session in 0-RTT mode using PSK. A
simplified TLS 1.3 handshake with 0-RTT DOTS signal message
exchange is shown in Figure 22.
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DOTS Client DOTS Server
ClientHello
(Finished)
(0-RTT DOTS signal message)
(end_of_early_data) -------->
ServerHello
{EncryptedExtensions}
{ServerConfiguration}
{Certificate}
{CertificateVerify}
{Finished}
<-------- [DOTS signal message]
{Finished} -------->
[DOTS signal message] <-------> [DOTS signal message]
Figure 22: TLS 1.3 handshake with 0-RTT
9. Mutual Authentication of DOTS Agents & Authorization of DOTS Clients
(D)TLS based on client certificate can be used for mutual
authentication between DOTS agents. If a DOTS gateway is involved,
DOTS clients and DOTS gateway MUST perform mutual authentication;
only authorized DOTS clients are allowed to send DOTS signals to a
DOTS gateway. DOTS gateway and DOTS server MUST perform mutual
authentication; DOTS server only allows DOTS signals from authorized
DOTS gateway, creating a two-link chain of transitive authentication
between the DOTS client and the DOTS server.
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+-------------------------------------------------+
| example.com domain +---------+ |
| | AAA | |
| +---------------+ | Server | |
| | Application | +------+--+ |
| | server + ^
| | (DOTS client) |<-----------------+ | |
| +---------------+ + | | example.net domain
| V V |
| +-------------+ | +---------------+
| +--------------+ | | | | |
| | Guest +<-----x----->+ +<---------------->+ DOTS |
| | (DOTS client)| | DOTS | | | Server |
| +--------------+ | Gateway | | | |
| +----+--------+ | +---------------+
| ^ |
| | |
| +----------------+ | |
| | DDOS detector | | |
| | (DOTS client) +<--------------+ |
| +----------------+ |
| |
+-------------------------------------------------+
Figure 23: Example of Authentication and Authorization of DOTS Agents
In the example depicted in Figure 23, the DOTS gateway and DOTS
clients within the 'example.com' domain mutually authenticate with
each other. 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 detector to request DDOS mitigation, but does not permit the
user of type 'guest' to request DDOS mitigation.
Also, DOTS gateway and DOTS server MUST perform mutual authentication
using certificates. A DOTS server will only allow a DOTS gateway
with a certificate for a particular domain to request mitigation for
that domain. In reference to Figure 23, the DOTS server only allows
the DOTS gateway to request mitigation for 'example.com' domain and
not for other domains.
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10. IANA Considerations
This specification registers new parameters for DOTS signal channel
and establishes registries for mappings to CBOR.
10.1. DOTS signal channel CBOR Mappings Registry
A new registry will be requested from IANA, entitled "DOTS signal
channel CBOR Mappings Registry". The registry is to be created as
Expert Review Required.
10.1.1. Registration Template
Parameter name:
Parameter names (e.g., "target_ip") in the DOTS signal channel.
CBOR Key Value:
Key value for the parameter. The key value MUST be an integer in
the range of 1 to 65536. The key values in the range of 32768 to
65536 are assigned for Vendor-Specific parameters.
CBOR Major Type:
CBOR Major type and optional tag for the claim.
Change Controller:
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.
Specification Document(s):
Reference to the document or documents that specify the parameter,
preferably including URIs that can be used to retrieve copies of
the documents. An indication of the relevant sections may also be
included but is not required.
10.1.2. Initial Registry Contents
o Parameter Name: "mitigation-scope"
o CBOR Key Value: 1
o CBOR Major Type: 5
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: "scope"
o CBOR Key Value: 2
o CBOR Major Type: 5
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: "policy-id"
o CBOR Key Value: 3
o CBOR Major Type: 0
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o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name:target-ip
o CBOR Key Value: 4
o CBOR Major Type: 4
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: target-port-range
o CBOR Key Value: 5
o CBOR Major Type: 4
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: "lower-port"
o CBOR Key Value: 6
o CBOR Major Type: 0
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: "upper-port"
o CBOR Key Value: 7
o CBOR Major Type: 0
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: target-protocol
o CBOR Key Value: 8
o CBOR Major Type: 4
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: "FQDN"
o CBOR Key Value: 9
o CBOR Major Type: 4
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: "URI"
o CBOR Key Value: 10
o CBOR Major Type: 4
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: "E.164"
o CBOR Key Value: 11
o CBOR Major Type: 4
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o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: alias
o CBOR Key Value: 12
o CBOR Major Type: 4
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: "lifetime"
o CBOR Key Value: 13
o CBOR Major Type: 0
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: attack-status
o CBOR Key Value: 14
o CBOR Major Type: 0
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: signal-config
o CBOR Key Value: 15
o CBOR Major Type: 5
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: heartbeat-interval
o CBOR Key Value: 16
o CBOR Major Type: 0
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: max-retransmit
o CBOR Key Value: 17
o CBOR Major Type: 0
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: ack-timeout
o CBOR Key Value: 18
o CBOR Major Type: 0
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: ack-random-factor
o CBOR Key Value: 19
o CBOR Major Type: 7
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o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: MinValue
o CBOR Key Value: 20
o CBOR Major Type: 0
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: MaxValue
o CBOR Key Value: 21
o CBOR Major Type: 0
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: status
o CBOR Key Value: 22
o CBOR Major Type: 0
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: bytes_dropped
o CBOR Key Value: 23
o CBOR Major Type: 0
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: bps_dropped
o CBOR Key Value: 24
o CBOR Major Type: 0
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: pkts_dropped
o CBOR Key Value: 25
o CBOR Major Type: 0
o Change Controller: IESG
o Specification Document(s): this document
o Parameter Name: pps_dropped
o CBOR Key Value: 26
o CBOR Major Type: 0
o Change Controller: IESG
o Specification Document(s): this document
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11. Security Considerations
Authenticated encryption MUST be used for data confidentiality and
message integrity. (D)TLS based on client certificate MUST be used
for mutual authentication. 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 [RFC7525] MUST be followed to
avoid attacks on (D)TLS.
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 [RFC5925]. 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.
Special care should be taken in order to ensure that the activation
of the proposed mechanism won't have an impact on the stability of
the network (including connectivity and services delivered over that
network).
Involved functional elements in the cooperation system must establish
exchange instructions and notification over a secure and
authenticated channel. Adequate filters can be enforced to avoid
that nodes outside a trusted domain can inject request such as
deleting filtering rules. Nevertheless, attacks can be initiated
from within the trusted domain if an entity has been corrupted.
Adequate means to monitor trusted nodes should also be enabled.
12. Contributors
The following individuals have contributed to this document:
Mike Geller Cisco Systems, Inc. 3250 Florida 33309 USA Email:
mgeller@cisco.com
Robert Moskowitz HTT Consulting Oak Park, MI 42837 United States
Email: rgm@htt-consult.com
Dan Wing Email: dwing-ietf@fuggles.com
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13. Acknowledgements
Thanks to Christian Jacquenet, Roland Dobbins, Andrew Mortensen,
Roman D. Danyliw, Michael Richardson, Ehud Doron, Kaname Nishizuka,
Dave Dolson and Gilbert Clark for the discussion and comments.
14. References
14.1. Normative References
[I-D.ietf-core-coap-tcp-tls]
Bormann, C., Lemay, S., Tschofenig, H., Hartke, K.,
Silverajan, B., and B. Raymor, "CoAP (Constrained
Application Protocol) over TCP, TLS, and WebSockets",
draft-ietf-core-coap-tcp-tls-06 (work in progress),
February 2017.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[RFC5925] Touch, J., Mankin, A., and R. Bonica, "The TCP
Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
June 2010, <http://www.rfc-editor.org/info/rfc5925>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>.
[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
Weiler, S., and T. Kivinen, "Using Raw Public Keys in
Transport Layer Security (TLS) and Datagram Transport
Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
June 2014, <http://www.rfc-editor.org/info/rfc7250>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>.
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[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <http://www.rfc-editor.org/info/rfc7525>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<http://www.rfc-editor.org/info/rfc7641>.
14.2. Informative References
[I-D.ietf-core-comi]
Stok, P., Bierman, A., Veillette, M., and A. Pelov, "CoAP
Management Interface", draft-ietf-core-comi-00 (work in
progress), January 2017.
[I-D.ietf-core-yang-cbor]
Veillette, M., Pelov, A., Somaraju, A., Turner, R., and A.
Minaburo, "CBOR Encoding of Data Modeled with YANG",
draft-ietf-core-yang-cbor-04 (work in progress), February
2017.
[I-D.ietf-dots-architecture]
Mortensen, A., Andreasen, F., Reddy, T.,
christopher_gray3@cable.comcast.com, c., Compton, R., and
N. Teague, "Distributed-Denial-of-Service Open Threat
Signaling (DOTS) Architecture", draft-ietf-dots-
architecture-01 (work in progress), October 2016.
[I-D.ietf-dots-requirements]
Mortensen, A., Moskowitz, R., and T. Reddy, "Distributed
Denial of Service (DDoS) Open Threat Signaling
Requirements", draft-ietf-dots-requirements-03 (work in
progress), October 2016.
[I-D.ietf-dots-use-cases]
Dobbins, R., Fouant, S., Migault, D., Moskowitz, R.,
Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS
Open Threat Signaling", draft-ietf-dots-use-cases-03 (work
in progress), November 2016.
[I-D.ietf-tls-tls13]
Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", draft-ietf-tls-tls13-18 (work in progress),
October 2016.
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[I-D.ietf-tsvwg-rfc5405bis]
Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", draft-ietf-tsvwg-rfc5405bis-19 (work in
progress), October 2016.
[I-D.reddy-dots-data-channel]
Reddy, T., Boucadair, M., Nishizuka, K., Xia, L., Patil,
P., Mortensen, A., and N. Teague, "Distributed Denial-of-
Service Open Threat Signaling (DOTS) Data Channel", draft-
reddy-dots-data-channel-04 (work in progress), February
2017.
[I-D.rescorla-tls-dtls13]
Rescorla, E. and H. Tschofenig, "The Datagram Transport
Layer Security (DTLS) Protocol Version 1.3", draft-
rescorla-tls-dtls13-00 (work in progress), October 2016.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<http://www.rfc-editor.org/info/rfc791>.
[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing
(CIDR): The Internet Address Assignment and Aggregation
Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August
2006, <http://www.rfc-editor.org/info/rfc4632>.
[RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet
Denial-of-Service Considerations", RFC 4732,
DOI 10.17487/RFC4732, December 2006,
<http://www.rfc-editor.org/info/rfc4732>.
[RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common
Mitigations", RFC 4987, DOI 10.17487/RFC4987, August 2007,
<http://www.rfc-editor.org/info/rfc4987>.
[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
January 2008, <http://www.rfc-editor.org/info/rfc5077>.
[RFC6520] Seggelmann, R., Tuexen, M., and M. Williams, "Transport
Layer Security (TLS) and Datagram Transport Layer Security
(DTLS) Heartbeat Extension", RFC 6520,
DOI 10.17487/RFC6520, February 2012,
<http://www.rfc-editor.org/info/rfc6520>.
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[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with
Dual-Stack Hosts", RFC 6555, DOI 10.17487/RFC6555, April
2012, <http://www.rfc-editor.org/info/rfc6555>.
[RFC6724] Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
"Default Address Selection for Internet Protocol Version 6
(IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
<http://www.rfc-editor.org/info/rfc6724>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <http://www.rfc-editor.org/info/rfc7049>.
[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
<http://www.rfc-editor.org/info/rfc7413>.
[RFC7918] Langley, A., Modadugu, N., and B. Moeller, "Transport
Layer Security (TLS) False Start", RFC 7918,
DOI 10.17487/RFC7918, August 2016,
<http://www.rfc-editor.org/info/rfc7918>.
[RFC7924] Santesson, S. and H. Tschofenig, "Transport Layer Security
(TLS) Cached Information Extension", RFC 7924,
DOI 10.17487/RFC7924, July 2016,
<http://www.rfc-editor.org/info/rfc7924>.
Authors' Addresses
Tirumaleswar Reddy
Cisco Systems, Inc.
Cessna Business Park, Varthur Hobli
Sarjapur Marathalli Outer Ring Road
Bangalore, Karnataka 560103
India
Email: tireddy@cisco.com
Mohamed Boucadair
Orange
Rennes 35000
France
Email: mohamed.boucadair@orange.com
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Prashanth Patil
Cisco Systems, Inc.
Email: praspati@cisco.com
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