| DOTS | T. Reddy |
| Internet-Draft | D. Wing |
| Intended status: Standards Track | P. Patil |
| Expires: September 17, 2016 | M. Geller |
| Cisco | |
| M. Boucadair | |
| Orange | |
| R. Moskowitz | |
| HTT Consulting | |
| March 16, 2016 |
Co-operative DDoS Mitigation
draft-reddy-dots-transport-03
This document discusses mechanisms that a DOTS client can use, when it detects a potential Distributed Denial-of-Service (DDoS) attack, to signal that the DOTS client is under an attack or request an upstream DOTS server to perform inbound filtering in its ingress routers for traffic that the DOTS client wishes to drop. The DOTS server can then undertake appropriate actions (including, blackhole, drop, rate-limit, or add to watch list) on the suspect traffic to the DOTS client, thus reducing the effectiveness of the attack.
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This Internet-Draft will expire on September 17, 2016.
Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved.
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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 DOTS server 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 DOTS server 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 the proposed mechanism is that the DOTS server can provide protection to the DOTS client from bandwidth-saturating DDoS traffic.
How a DOTS server 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].
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].
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 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:
A network diagram showing a deployment of these elements is shown below. This shows the DOTS server operating on the access network.
Network Resource CPE router Access network __________ +-----------+ +----------+ +-------------+ / \ | |____| |_______| |___ | Internet | |DOTS client| |DOTS relay| | DOTS server | | | | | | | | | | | +-----------+ +----------+ +-------------+ \__________/
Figure 1
The DOTS server can also be running on the Internet, as depicted below:
Network Resource CPE router __________ DDoS mitigation svc +-----------+ +----------+ / \ +-------------+ | |____| |_______| |___ | | |DOTS client| |DOTS relay| | 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 a company, while the DOTS server is owned and operated by a different company providing DDoS mitigation services. That company 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 the DOTS relay.
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. 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.
DOTS client and server can also use the following techniques to reduce the delay required to deliver a DOTS signal:
A DOTS client can use RESTful APIs discussed in this section to signal/inform a DOTS server of an attack.
TBD: 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 the HTTP protocol, 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.
JSON [RFC7159] payloads is be used to convey signal channel specific payload messages that convey request parameters and response information such as errors.
The following APIs define the means to convey a DOTS signal from a DOTS client to a DOTS server. POST request is used to convey the DOTS signal from a DOTS client to a DOTS server over the signal channel, possibly traversing a DOTS relay, indicating the DOTS client's need for mitigation, as well as the scope of any requested mitigation (Section 6.1.1).
DELETE requests are used by the DOTS client to withdraw the request for mitigation from the DOTS server (Section 6.1.2).
GET requests are used by the DOTS client to retrieve the DOTS signal(s) it had conveyed to the DOTS server (Section 6.1.3).
PUT requests are used by the DOTS client to convey mitigation efficacy updates to the DOTS server (Section 6.1.4).
An HTTP POST request is used to convey a DOTS signal to the DOTS server (Figure 4).
POST {scheme}://{host}:{port}/.well-known/{version}/{URI suffix for DOTS signal}
Accept: application/json
Content-type: application/json
{
"policy-id": "number",
"target-ip": "string",
"target-port": "string",
"target-protocol": "string",
"lifetime": "number"
}
Figure 4: POST to convey DOTS signals
The header fields are described below.
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 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 5 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 https://www.example.com/.well-known/v1/DOTS signal
Accept: application/json
Content-type: application/json
{
"policy-id":123321333242,
"target-ip":[
"2002:db8:6401::1",
"2002:db8:6401::2"
],
"target-port":[
"80",
"8080",
"443"
],
"target-protocol":"tcp"
}
Figure 5: POST for DOTS signal
The DOTS server indicates the result of processing the POST request using HTTP response codes. HTTP 2xx codes are success, HTTP 4xx codes are some sort of invalid request and HTTP 5xx codes are returned if the DOTS server has erred or is incapable of performing the mitigation. Response code 200 (OK) 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 400 (Bad Request) will be returned in the response or if the request contains invalid or unknown parameters then 400 (Invalid query) will be returned in the response. The HTTP response will include the JSON body received in the request.
An HTTP DELETE request is used to withdraw a DOTS signal from a DOTS server (Figure 6).
DELETE {scheme}://{host}:{port}/.well-known/{URI suffix for DOTS signal}
Accept: application/json
Content-type: application/json
{
"policy-id": "number"
}
Figure 6: 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 "404" HTTP error response code. The DOTS server successfully acknowledges a DOTS client's request to withdraw the DOTS signal using 200 (OK) response code, and ceases mitigation activity as quickly as possible.
An HTTP GET request is used to retrieve information and status of a DOTS signal from a DOTS server (Figure 7). 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 404 HTTP 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
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>
Figure 7: GET to retrieve the rules
Figure 8 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 8: Response body
The various possible values of status field are explained below:
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 HTTP PUT request (Figure 9) 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 6.1.1). If the DOTS server does not find the policy number conveyed in the PUT request in its policy state data, it responds with a 404 HTTP error response code.
PUT {scheme}://{host}:{port}/.well-known/{URI suffix for DOTS signal}/<policy-id number>
Accept: application/json
Content-type: application/json
{
"target-ip": "string",
"target-port": "string",
"target-protocol": "string",
"lifetime": "number",
"attack-status": "string"
}
Figure 9: Efficacy Update
The 'attack-status' field is a mandatory attribute. The various possible values contained in the 'attack-status' field are explained below:
A DOTS client can use RESTful APIs to provision and manage filters on the DOTS server. TBD: 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 [RFC7159] 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 the DOTS server via the DOTS relay is discussed below:
The DOTS conveys the black-list rules to the DOTS relay. The DOTS relay 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 relay is authorized to signal the black-list rules. To create or purge filters, the DOTS client sends HTTP requests to the DOTS relay. The DOTS relay acts as an proxy, validates the rules and proxies the requests containing the black-listed IP addresses to the DOTS server. When the DOTS relay receives the associated HTTP response from the DOTS server, it propagates the response back to the DOTS client. If an attack is detected by the DOTS relay then it can act as a DOTS client and signal the black-list rules to the DOTS server. The DOTS relay plays the role of both client and proxy.
The following APIs define means for a DOTS client to configure filtering rules on a DOTS server.
An HTTP POST request is used to push filtering rules to a DOTS server (Figure 10).
POST {scheme}://{host}:{port}/.well-known/{version}/{URI suffix for filtering}
Accept: application/json
Content-type: 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 10: POST to install filtering rules
The header fields are described below:
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 11 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 https://www.example.com/.well-known/v1/filter
Accept: application/json
Content-type: 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 11: POST to Install Black-list Rules
An HTTP DELETE request is used to delete filtering rules from a DOTS server (Figure 12).
DELETE {scheme}://{host}:{port}/.well-known/{URI suffix for filtering}
Accept: application/json
Content-type: application/json
{
"policy-id": "number"
}
Figure 12: DELETE to remove the rules
An HTTP GET request is used to retrieve filtering rules from a DOTS server.
Figure 13 shows an example to retrieve all the black-lists rules programmed by the DOTS client while Figure 14 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 13: GET to retrieve the rules (1)
GET {scheme}://{host}:{port}/.well-known/{URI suffix for filtering}
Accept: application/json
Content-type: application/json
{
"policy-id": "number"
}
Figure 14: GET to retrieve the rules (2)
TODO: show response
TODO
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.
Thanks to Christian Jacquenet, Roland Dobbins, Andrew Mortensen, Roman D. Danyliw, and Gilbert Clark for the discussion and comments.
| [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. |
| [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. |
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.