DOTS T. Reddy
Internet-Draft D. Wing
Intended status: Standards Track P. Patil
Expires: January 9, 2017 M. Geller
Cisco
M. Boucadair
Orange
R. Moskowitz
HTT Consulting
July 8, 2016

Co-operative DDoS Mitigation
draft-reddy-dots-transport-05

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 both DOTS signal and data channels. Happy Eyeballs considerations for the DOTS signal channel are also elaborated.

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 January 9, 2017.

Copyright Notice

Copyright (c) 2016 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.


Table of Contents

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 client, a router, a firewall, or an entire network, etc.

In a lot of cases, it may not be possible for an enterprise to determine the cause for an attack, but instead just realize that certain resources seem to be under attack. The document proposes that, in such cases, the DOTS client just inform the DOTS server that the enterprise is under a potential attack and that the Mitigator monitor traffic to the enterprise to mitigate any possible attack. This document also describes a means for an enterprise, which act as DOTS clients, to dynamically inform its DOTS server of the IP addresses or prefixes that are causing DDoS. A Mitigator can use this information to discard flows from such IP addresses reaching the customer network.

The proposed mechanism can also be used between applications from various vendors that are deployed within the same network, some of them are responsible for monitoring and detecting attacks while others are responsible for enforcing policies on appropriate network elements. This cooperations contributes to a ensure a highly automated network that is also robust, reliable and secure. The advantage of this mechanism is that the DOTS server can provide protection to the DOTS client from bandwidth-saturating DDoS traffic.

How a Mitigator determines which network elements should be modified to install appropriate filtering rules is out of scope. A variety of mechanisms and protocols (including NETCONF) may be considered to exchange information through a communication interface between the server and these underlying elements; the selection of appropriate mechanisms and protocols to be invoked for that interfaces is deployment-specific.

Terminology and protocol requirements for co-operative DDoS mitigation are obtained from [I-D.ietf-dots-requirements].

2. Notational Conventions

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].

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 an application uses these resources to offer its intended task in the most efficient fashion. However, an attacker may be able to prevent the 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, some of the possible arrangements to mitigate the attack are:

An example of network diagram showing a deployment of these elements is shown in Figure 1. In this example, the DOTS server 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 with the DOTS server via a DOTS gateway.

4. Happy Eyeballs for DOTS Signal Channel

DOTS signaling can happen with DTLS over UDP and TLS 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 [RFC6347] with the DOTS server and will, then, have to fall back to TLS over TCP [RFC5246] 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.

5. DOTS Signal Channel

5.1. Overview

Constrained Application Protocol (CoAP) [RFC7252] is used for DOTS signal channel. 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, etc.

          +--------------+
          |    DOTS      |
          +--------------+
          |     CoAP     |
          +--------------+
          | TLS |  DTLS  |
          +--------------+
          | TCP |   UDP  |
          +--------------+
          |    IP        |
          +--------------+

Figure 4: Abstract Layering of DOTS signal channel over CoAP over (D)TLS

JSON [RFC7159] payloads is 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 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.

TBD: Do we want any of the above requests to be Non-confirmable ?

5.2.1. Convey DOTS Signals

A POST request is used to convey a DOTS signal to the DOTS server (Figure 5).

  POST {scheme}://{host}:{port}/.well-known/{version}/{URI suffix for DOTS signal}
  Accept: application/json
  Content-Format: application/json
  {
     "policy-id": "number",     
     "target-ip": "string",
     "target-port": "string",     
     "target-protocol": "string",
     "lifetime": "number"
   }

Figure 5: POST to convey DOTS signals

The header fields are described below.

policy-id:
Identifier of the policy represented using a number. 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. This is an optional attribute.
target-port:
A list of ports under attack. This is an optional attribute.
target-protocol:
A list of protocols under attack. Valid protocol values include tcp, udp, sctp, and dccp. 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.

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.

If the DOTS server is not able to respond immediately to a POST request carried in a Confirmable message, it simply responds with an Empty Acknowledgement message so that the DOTS client can stop retransmitting the request. 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]).

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 and 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.

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.

  POST coaps://www.example.com/.well-known/v1/DOTS signal
  Accept: application/json
  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 request 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.

5.2.2. Withdraw a DOTS Signal

A DELETE request is used to withdraw a DOTS signal from a DOTS server (Figure 7).

  DELETE {scheme}://{host}:{port}/.well-known/{URI suffix for DOTS signal}
  Accept: application/json
  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.

1) To retrieve all DOTS signals signaled by the DOTS client.
  
GET {scheme}://{host}:{port}/.well-known/{URI suffix for DOTS signal}/list
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.

GET {scheme}://{host}:{port}/.well-known/{URI suffix for DOTS signal}/<policy-id number>
Observe : 0

Figure 8: GET to retrieve the rules

Figure 9 shows the response of all the active policies on the DOTS server.

{
  "policy-data":[
    {
      "policy-id":123321333242,
      "target-prtoocol":"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.

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.

                       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 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.

  PUT {scheme}://{host}:{port}/.well-known/{URI suffix for DOTS signal}/<policy-id number>
  Accept: application/json
  Content-Format: application/json
  {  
     "target-ip": "string",
     "target-port": "string",     
     "target-protocol": "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).

6. DOTS Data Channel

The data channel is intended to be used for bulk data exchanges and requires a reliable transport, CoAP over TLS over TCP is used for data channel.

JSON payloads is used to convey both filtering rules as well as data channel specific payload messages that convey request parameters and response information such as errors. All data channel URIs defined in this document, and in subsequent documents, MUST NOT have a URI containing "/DOTS signal".

One of the possible arrangements for DOTS client to signal filtering rules to a DOTS server via the DOTS gateway is discussed below:

The DOTS conveys the black-list rules to the DOTS gateway. The DOTS gateway validates if the DOTS client is authorized to signal the black-list rules and if the client is authorized propagates the rules to the DOTS server. Likewise, the DOTS server validates if the DOTS gateway is authorized to signal the black-list rules. To create or purge filters, the DOTS client sends CoAP requests to the DOTS gateway. The DOTS gateway acts as a proxy, validates the rules and proxies the requests containing the black-listed IP addresses to a DOTS server. When the DOTS gateway receives the associated CoAP response from the DOTS server, it propagates the response back to the DOTS client. If an attack is detected by the DOTS gateway then it can act as a DOTS client and signal the black-list rules to the DOTS server. The DOTS gateway plays the role of both client and server.

6.1. Filtering Rules

The following APIs define means for a DOTS client to configure filtering rules on a DOTS server.

6.1.1. Install Filtering Rules

An POST request is used to push filtering rules to a DOTS server (Figure 12).

  POST {scheme}://{host}:{port}/.well-known/{version}/{URI suffix for filtering}
  Accept: application/json
  Content-Format: application/json
  {
     "policy-id": "number",
     "traffic-protocol": "string",
     "source-protocol-port": "string", 
     "destination-protocol-port": "string",
     "destination-ip": "string",
     "source-ip": "string",
     "lifetime": "number",
     "traffic-rate" : "number"
   }

Figure 12: POST to install filtering rules

The header fields are described below:

policy-id:
Identifier of the policy represented using a number. 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 client. This document does not make any assumption about how this identifier is generated. This is an mandatory attribute.
traffic-protocol:
Valid protocol values include tcp, udp, sctp, and dccp. This is an mandatory attribute.
source-protocol-port:
The source port number, port number range (using "-"). For TCP, UDP, SCTP, or DCCP: the source range of ports (e.g., 1024-65535). This is an optional attribute.
destination-protocol-port:
The destination port number, port number range (using "-"). For TCP, UDP, SCTP, or DCCP: the destination range of ports (e.g., 443-443). This information is useful to avoid disturbing a group of customers when address sharing is in use [RFC6269]. This is an optional attribute.
destination-ip:
The destination IP address, IP addresses separated by commas, or prefixes using "/" notation. This is an optional attribute.
source-ip:
The source IP addresses, IP addresses separated by commas, or prefixes using "/" notation. This is an optional attribute.
lifetime:
Lifetime of the rule in seconds. Upon the expiry of this lifetime, and if the request is not refreshed, this particular rule is removed. The rule can be refreshed by sending the same message again. The default lifetime of the rule 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 rule where the client has unexpectedly quit in a timely manner. A lifetime of zero indicates indefinite lifetime for the rule. The server MUST always indicate the actual lifetime in the response. This is an optional attribute in the request.
traffic-rate:
This is the allowed traffic rate in bytes per second indicated in IEEE floating point [IEEE.754.1985] format. The value 0 indicates all traffic for the particular flow to be discarded. This is a mandatory attribute.

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.

Figure 13 shows a POST request to block traffic from attacker IPv6 prefix 2001:db8:abcd:3f01::/64 to network resource using IPv6 address 2002:db8:6401::1 to operate a server on TCP port 443.

  POST coaps://www.example.com/.well-known/v1/filter
  Accept: application/json
  Content-Format: application/json
   {
     "policy-id": 123321333242,
     "traffic-protocol": "tcp",
     "source-protocol-port": "0-65535", 
     "destination-protocol-port": "443",
     "destination-ip": "2001:db8:abcd:3f01::/64",
     "source-ip": "2002:db8:6401::1", 
     "lifetime": 1800,
     "traffic-rate": 0
   }

Figure 13: POST to Install Black-list Rules

6.1.2. Remove Filtering Rules

A DELETE request is used to delete filtering rules from a DOTS server (Figure 14).

  DELETE {scheme}://{host}:{port}/.well-known/{URI suffix for filtering}
  Accept: application/json
  Content-Format: application/json
   {
     "policy-id": "number"
   }

Figure 14: DELETE to remove the rules

6.1.3. Retrieving Installed Filtering Rules

A GET request is used to retrieve filtering rules from a DOTS server.

Figure 15 shows an example to retrieve all the black-lists rules programmed by the DOTS client while Figure 16 shows an example to retrieve specific black-list rules programmed by the DOTS client.

GET {scheme}://{host}:{port}/.well-known/{URI suffix for filtering} 

Figure 15: GET to retrieve the rules (1)

GET {scheme}://{host}:{port}/.well-known/{URI suffix for filtering} 
Accept: application/json
Content-Format: application/json
{
   "policy-id": "number"
}

Figure 16: GET to retrieve the rules (2)

TODO: show response

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 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:

  • DOTS client can use (D)TLS session resumption without server-side state [RFC5077] to resume session and convey the DOTS signal.
  • While the communication to the DOTS server is quiescent, the DOTS client may want to 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.
    • 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:

  • 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.
  • 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.
  • TCP Fast Open [RFC7413] can reduce the number of round-trips to convey DOTS signal.

8. 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 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 17: Example of Authentication and Authorization of DOTS Agents

Figure 17, 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 17, the DOTS server only allows the DOTS gateway to request mitigation for 'example.com' domain and not for other domains.

9. IANA Considerations

TODO

10. 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 ciphersuite 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, 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.

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.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008.
[RFC5925] Touch, J., Mankin, A. and R. Bonica, "The TCP Authentication Option", RFC 5925, DOI 10.17487/RFC5925, June 2010.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January 2012.
[RFC7250] Wouters, P., Tschofenig, H., 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.
[RFC7252] Shelby, Z., Hartke, K. and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014.
[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.
[RFC7641] Hartke, K., "Observing Resources in the Constrained Application Protocol (CoAP)", RFC 7641, DOI 10.17487/RFC7641, September 2015.

12.2. Informative References

[I-D.ietf-dots-requirements] Mortensen, A., Moskowitz, R. and T. Reddy, "Distributed Denial of Service (DDoS) Open Threat Signaling Requirements", Internet-Draft draft-ietf-dots-requirements-01, March 2016.
[I-D.ietf-tls-cached-info] Santesson, S. and H. Tschofenig, "Transport Layer Security (TLS) Cached Information Extension", Internet-Draft draft-ietf-tls-cached-info-23, May 2016.
[I-D.ietf-tls-falsestart] Langley, A., Modadugu, N. and B. Moeller, "Transport Layer Security (TLS) False Start", Internet-Draft draft-ietf-tls-falsestart-02, May 2016.
[IEEE.754.1985] Institute of Electrical and Electronics Engineers, "Standard for Binary Floating-Point Arithmetic", August 1985.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI 10.17487/RFC0791, September 1981.
[RFC4732] Handley, M., Rescorla, E. and IAB, "Internet Denial-of-Service Considerations", RFC 4732, DOI 10.17487/RFC4732, December 2006.
[RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common Mitigations", RFC 4987, DOI 10.17487/RFC4987, August 2007.
[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.
[RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J. and D. McPherson, "Dissemination of Flow Specification Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009.
[RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P. and P. Roberts, "Issues with IP Address Sharing", RFC 6269, DOI 10.17487/RFC6269, June 2011.
[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.
[RFC6555] Wing, D. and A. Yourtchenko, "Happy Eyeballs: Success with Dual-Stack Hosts", RFC 6555, DOI 10.17487/RFC6555, April 2012.
[RFC6724] Thaler, D., Draves, R., Matsumoto, A. and T. Chown, "Default Address Selection for Internet Protocol Version 6 (IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012.
[RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March 2014.
[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S. and A. Jain, "TCP Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014.

Appendix A. BGP

BGP defines a mechanism as described in [RFC5575] that can be used to automate inter-domain coordination of traffic filtering, such as what is required in order to mitigate DDoS attacks. However, support for BGP in an access network does not guarantee that traffic filtering will always be honored. Since a DOTS client will not receive an acknowledgment for the filtering request, the DOTS client should monitor and apply similar rules in its own network in cases where the DOTS server is unable to enforce the filtering rules. In addition, enforcement of filtering rules of BGP on Internet routers are usually governed by the maximum number of data elements the routers can hold as well as the number of events they are able to process in a given unit of time.

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
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
Mike Geller Cisco Systems, Inc. 3250 Florida 33309 USA EMail: mgeller@cisco.com
Mohamed Boucadair Orange Rennes, 35000 France EMail: mohamed.boucadair@orange.com
Robert Moskowitz HTT Consulting Oak Park, MI, 42837 United States EMail: rgm@htt-consult.com