| 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
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.
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 (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 (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.
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].
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].
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.
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.
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).
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.
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 [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.
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
This document defines the YANG module "ietf-dots-signal", which has the following structure:
<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 {
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;
description "lifetime";
}
}
}
}
<CODE ENDS>
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
This document defines the YANG module "ietf-dots-signal-config", which has the following structure:
<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>
The following APIs define the means to convey a DOTS signal from a DOTS client to a DOTS server:
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 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).
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.
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.
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 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
}
],
"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
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.
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.
{
"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.
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.
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
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.
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.
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:
/--------------------+------------------------------------------------------\ | 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.
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 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.
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
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.
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:
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.
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
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.
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.
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
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:
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.
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 an Ping message and the peer DOTS agent will respond by sending an single Pong message.
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
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:
Implementations compliant with this profile SHOULD implement all of the following items to reduce the delay required to deliver a DOTS signal:
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 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.
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:
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
(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.
+-------------------------------------------------+ | 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
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.
This specification registers new parameters for DOTS signal channel and establishes registries for mappings to CBOR.
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.
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.
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
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.