DOTS T. Reddy
Internet-Draft Cisco
Intended status: Standards Track M. Boucadair
Expires: April 1, 2017 Orange
D. Wing
P. Patil
Cisco
September 28, 2016
Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal
Channel
draft-reddy-dots-signal-channel-01
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 April 1, 2017.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
Reddy, et al. Expires April 1, 2017 [Page 1]
Internet-Draft DOTS Signal Channel September 2016
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(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
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Notational Conventions and Terminology . . . . . . . . . . . 3
3. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 3
4. Happy Eyeballs for DOTS Signal Channel . . . . . . . . . . . 5
5. DOTS Signal Channel . . . . . . . . . . . . . . . . . . . . . 6
5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Mitigation Service Requests . . . . . . . . . . . . . . . 7
5.2.1. Convey DOTS Signals . . . . . . . . . . . . . . . . . 8
5.2.2. Withdraw a DOTS Signal . . . . . . . . . . . . . . . 12
5.2.3. Retrieving a DOTS Signal . . . . . . . . . . . . . . 12
5.2.4. Efficacy Update from DOTS Client . . . . . . . . . . 16
6. (D)TLS Protocol Profile and Performance considerations . . . 17
7. Mutual Authentication of DOTS Agents & Authorization of DOTS
Clients . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
9. Security Considerations . . . . . . . . . . . . . . . . . . . 20
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 20
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
12.1. Normative References . . . . . . . . . . . . . . . . . . 21
12.2. Informative References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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 enterprise 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
Reddy, et al. Expires April 1, 2017 [Page 2]
Internet-Draft DOTS Signal Channel September 2016
[I-D.ietf-dots-architecture], proposes that, in such cases, the DOTS
client just inform its DOTS server(s) that the enterprise is under a
potential attack and that the mitigator monitor traffic to the
enterprise 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.
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.
Reddy, et al. Expires April 1, 2017 [Page 3]
Internet-Draft DOTS Signal Channel September 2016
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.
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.
Reddy, et al. Expires April 1, 2017 [Page 4]
Internet-Draft DOTS Signal Channel September 2016
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
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).
Reddy, et al. Expires April 1, 2017 [Page 5]
Internet-Draft DOTS Signal Channel September 2016
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
UDP and TLS over TCP. 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.
Reddy, et al. Expires April 1, 2017 [Page 6]
Internet-Draft DOTS Signal Channel September 2016
+--------------+
| 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.
JSON [RFC7159] payloads are used to convey signal channel specific
payload messages that convey request parameters and response
information such as errors.
TBD: Do we want to use CBOR [RFC7049] instead of JSON?
5.2. Mitigation Service Requests
The following APIs define the means to convey a DOTS signal from a
DOTS client to a DOTS server:
POST 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 5.2.1).
DOTS gateway act as a CoAP-to-CoAP Proxy (explained in [RFC7252]).
DELETE requests: are used by the DOTS client to withdraw the request
for mitigation from the DOTS server (Section 5.2.2).
GET requests: are used by the DOTS client to retrieve the DOTS
signal(s) it had conveyed to the DOTS server (Section 5.2.3).
PUT requests: are used by the DOTS client to convey mitigation
efficacy updates to the DOTS server (Section 5.2.4).
Reliability is provided to the POST, DELETE, GET, and PUT requests by
marking them as Confirmable (CON) messages. As explained in
Section 2.1 of [RFC7252], a Confirmable message is retransmitted
Reddy, et al. Expires April 1, 2017 [Page 7]
Internet-Draft DOTS Signal Channel September 2016
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 piggback
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]).
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 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).
5.2.1. 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 POST request
is used to convey a DOTS signal to the DOTS server (Figure 5). 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.
Reddy, et al. Expires April 1, 2017 [Page 8]
Internet-Draft DOTS Signal Channel September 2016
Header: POST (Code=0.02)
Uri-Host: "host"
Uri-Path: ".well-known"
Uri-Path: "DOTS-signal"
Uri-Path: "version"
Content-Type: "application/json"
{
"policy-id": "integer",
"target-ip": "string",
"target-port": "string",
"target-protocol": "string",
"FQDN": "string",
"URI": "string",
"E.164": "string",
"alias": "string"
"lifetime": "number"
}
Figure 5: POST to convey DOTS signals
The header fields are described below.
policy-id: Identifier of the policy represented using an integer.
This identifier MUST be unique for each policy bound to the DOTS
client, i.e. ,the policy-id needs to be unique relative to the
active policies with 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 or prefixes under attack. IP
addresses and prefixes are separated by commas. Prefixes are
represented using CIDR notation [RFC4632]. This is an optional
attribute.
target-port: A list of ports under attack. Ports are separated by
commas and port number range (using "-"). 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. Valid protocol
values include tcp, udp, sctp, and dccp. Protocol values are
separated by commas. This is an optional attribute.
FQDN: Fully Qualified Domain Name, is the full name of a system,
rather than just its hostname. For example, "venera" is a
Reddy, et al. Expires April 1, 2017 [Page 9]
Internet-Draft DOTS Signal Channel September 2016
hostname, and "venera.isi.edu" is an FQDN. This is an optional
attribute.
URI: Uniform Resource Identifier (URI). This is an optional
attribute.
E.164: E.164 number. This is an optional attribute.
alias: Name of the alias (see Section 3.1.1 in
[I-D.reddy-dots-data-channel]). This is an optional attribute.
lifetime: Lifetime of the mitigation request policy 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 policy is 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 policy 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.
In the POST request at least one of the attributes target-ip or
target-port or target-protocol or FQDN or URI or E.164 or alias MUST
be present. The relative order of two rules is determined by
comparing their respective policy identifiers. The rule with lower
numeric policy identifier value has higher precedence (and thus will
match before) than the rule with higher numeric policy identifier
value.
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' field could be split
into multiple lists and each list conveyed in a new POST request.
Reddy, et al. Expires April 1, 2017 [Page 10]
Internet-Draft DOTS Signal Channel September 2016
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.
Figure 6 shows a POST request to signal that ports 80, 8080, and 443
on the servers 2002:db8:6401::1 and 2002:db8:6401::2 are being
attacked.
Header: POST (Code=0.02)
Uri-Host: "www.example.com"
Uri-Path: ".well-known"
Uri-Path: "v1"
Uri-Path: "DOTS-signal"
Content-Format: "application/json"
{
"policy-id":123321333242,
"target-ip":[
"2002:db8:6401::1",
"2002:db8:6401::2"
],
"target-port":[
"80",
"8080",
"443"
],
"target-protocol":"tcp"
}
Figure 6: POST for DOTS signal
The DOTS server indicates the result of processing the POST request
using CoAP response codes. CoAP 2xx codes are success, CoAP 4xx
codes are some sort of invalid requests and 5xx codes are returned if
the DOTS server has erred or is incapable of performing the
mitigation. Response code 2.01 (Created) will be returned in the
response if the DOTS server has accepted the mitigation request and
will try to mitigate the attack. 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. The CoAP response will include the JSON body received in
the request.
Reddy, et al. Expires April 1, 2017 [Page 11]
Internet-Draft DOTS Signal Channel September 2016
5.2.2. Withdraw a DOTS Signal
A DELETE request is used to withdraw a DOTS signal from a DOTS server
(Figure 7).
Header: DELETE (Code=0.04)
Uri-Host: "host"
Uri-Path: ".well-known"
Uri-Path: "version"
Uri-Path: "DOTS-signal"
Content-Format: "application/json"
{
"policy-id": "number"
}
Figure 7: Withdraw DOTS signal
If the DOTS server does not find the policy number conveyed in the
DELETE request in its policy state 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.
5.2.3. 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 number conveyed in the GET request in its policy
state data, then it responds with a 4.04 (Not Found) error response
code.
Reddy, et al. Expires April 1, 2017 [Page 12]
Internet-Draft DOTS Signal Channel September 2016
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"
Observe : 0
2) To retrieve a specific DOTS signal signaled by the DOTS client.
The policy information 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: "policy-id value"
Observe : 0
Figure 8: GET to retrieve the rules
Figure 9 shows the response of all the active policies on the DOTS
server.
Reddy, et al. Expires April 1, 2017 [Page 13]
Internet-Draft DOTS Signal Channel September 2016
{
"policy-data":[
{
"policy-id":123321333242,
"target-protocol":"tcp",
"lifetime":3600,
"status":"mitigation in progress"
},
{
"policy-id":123321333244,
"target-protocol":"udp",
"lifetime":1800,
"status":"mitigation complete"
},
{
"policy-id":123321333245,
"target-protocol":"tcp",
"lifetime":1800,
"status":"attack stopped"
}
]
}
Figure 9: Response body
The various possible values of status field are explained below:
mitigation in progress: Attack mitigation is in progress (e.g.,
changing the network path to re-route the inbound traffic to DOTS
mitigator).
mitigation complete: Attack is successfully mitigated (e.g., attack
traffic is dropped).
attack stopped: Attack has stopped and the DOTS client can withdraw
the mitigation request.
mitigation capacity exceeded: 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
Reddy, et al. Expires April 1, 2017 [Page 14]
Internet-Draft DOTS Signal Channel September 2016
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. 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.
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
5.2.3.1. 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
Reddy, et al. Expires April 1, 2017 [Page 15]
Internet-Draft DOTS Signal Channel September 2016
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.
5.2.4. 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 header fields used in the POST request to convey the DOTS signal
(Section 5.2.1). If the DOTS server does not find the policy number
conveyed in the PUT request in its policy state data, it responds
with a 4.04 (Not Found) error response code.
Header: PUT (Code=0.03)
Uri-Host: "host"
Uri-Path: ".well-known"
Uri-Path: "version"
Uri-Path: "DOTS-signal"
Uri-Path: "policy-id value"
Content-Format: "application/json"
{
"target-ip": "string",
"target-port": "string",
"target-protocol": "string",
"FQDN": "string",
"URI": "string",
"E.164": "string",
"alias": "string"
"lifetime": "number",
"attack-status": "string"
}
Figure 11: Efficacy Update
The 'attack-status' field is a mandatory attribute. The various
possible values contained in the 'attack-status' field are explained
below:
in-progress: DOTS client determines that it is still under attack.
terminated: Attack is successfully mitigated (e.g., attack traffic
is dropped).
Reddy, et al. Expires April 1, 2017 [Page 16]
Internet-Draft DOTS Signal Channel September 2016
6. (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
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 client can use (D)TLS session resumption without server-side
state [RFC5077] to resume session and convey the DOTS signal.
o While the communication to the DOTS server is quiescent, the DOTS
client MAY probe the server to ensure it has maintained
cryptographic state. 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.
* A (D)TLS heartbeat [RFC6520] verifies the DOTS server still has
DTLS state by returning a DTLS message. If the server has lost
state, it returns a DTLS Alert. Upon receipt of an
unauthenticated DTLS Alert, the DTLS client validates the Alert
is within the replay window (Section 4.1.2.6 of [RFC6347]). It
is difficult for the DTLS client to validate the DTLS Alert was
generated by the DTLS server in response to a request or was
generated by an on- or off-path attacker. Thus, upon receipt
of an in-window DTLS Alert, the client SHOULD continue re-
transmitting the DTLS packet (in the event the Alert was
spoofed), and at the same time it SHOULD initiate DTLS session
resumption.
* TLS runs over TCP, so a simple probe is a 0-length TCP packet
(a "window probe"). This verifies the TCP connection is still
working, which is also sufficient to prove the server has
retained TLS state, because if the server loses TLS state it
abandons the TCP connection. If the server has lost state, a
TCP RST is returned immediately.
Reddy, et al. Expires April 1, 2017 [Page 17]
Internet-Draft DOTS Signal Channel September 2016
* 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 [I-D.ietf-tls-falsestart] which reduces round-
trips by allowing the TLS second flight of messages
(ChangeCipherSpec) to also contain the DOTS signal.
o Cached Information Extension [I-D.ietf-tls-cached-info] 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. 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.
Reddy, et al. Expires April 1, 2017 [Page 18]
Internet-Draft DOTS Signal Channel September 2016
+-------------------------------------------------+
| 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 12: Example of Authentication and Authorization of DOTS Agents
In the example depicted in Figure 12, 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 12, the DOTS server only allows
the DOTS gateway to request mitigation for 'example.com' domain and
not for other domains.
Reddy, et al. Expires April 1, 2017 [Page 19]
Internet-Draft DOTS Signal Channel September 2016
8. IANA Considerations
TODO
[TBD: DOTS WG will probably have to do something similar to
https://tools.ietf.org/html/rfc7519#section-10, create JSON DOTS
claim registry and register the JSON attributes defined in this
specification].
9. 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.
10. Contributors
The following individuals have contributed to this document:
Mike Geller Cisco Systems, Inc. 3250 Florida 33309 USA Email:
mgeller@cisco.com
Reddy, et al. Expires April 1, 2017 [Page 20]
Internet-Draft DOTS Signal Channel September 2016
Robert Moskowitz HTT Consulting Oak Park, MI 42837 United States
Email: rgm@htt-consult.com
11. Acknowledgements
Thanks to Christian Jacquenet, Roland Dobbins, Andrew Mortensen,
Roman D. Danyliw, and Gilbert Clark for the discussion and comments.
12. References
12.1. Normative References
[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>.
[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>.
Reddy, et al. Expires April 1, 2017 [Page 21]
Internet-Draft DOTS Signal Channel September 2016
[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>.
12.2. Informative References
[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-00 (work in progress), July 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-02 (work in
progress), July 2016.
[I-D.ietf-dots-use-cases]
Dobbins, R., Fouant, S., Migault, D., Moskowitz, R.,
Teague, N., and L. Xia, "Use cases for DDoS Open Threat
Signaling", draft-ietf-dots-use-cases-01 (work in
progress), March 2016.
[I-D.ietf-tls-cached-info]
Santesson, S. and H. Tschofenig, "Transport Layer Security
(TLS) Cached Information Extension", draft-ietf-tls-
cached-info-23 (work in progress), May 2016.
[I-D.ietf-tls-falsestart]
Langley, A., Modadugu, N., and B. Moeller, "Transport
Layer Security (TLS) False Start", draft-ietf-tls-
falsestart-02 (work in progress), May 2016.
[I-D.reddy-dots-data-channel]
Reddy, T., Wing, D., Boucadair, M., Nishizuka, K., and L.
Xia, "Distributed Denial-of-Service Open Threat Signaling
(DOTS) Data Channel", draft-reddy-dots-data-channel-00
(work in progress), August 2016.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<http://www.rfc-editor.org/info/rfc791>.
Reddy, et al. Expires April 1, 2017 [Page 22]
Internet-Draft DOTS Signal Channel September 2016
[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>.
[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>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <http://www.rfc-editor.org/info/rfc7159>.
[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>.
Authors' Addresses
Reddy, et al. Expires April 1, 2017 [Page 23]
Internet-Draft DOTS Signal Channel September 2016
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
Dan Wing
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, California 95134
USA
Email: dwing@cisco.com
Prashanth Patil
Cisco Systems, Inc.
Email: praspati@cisco.com
Reddy, et al. Expires April 1, 2017 [Page 24]