| DOTS | T. Reddy |
| Internet-Draft | D. Wing |
| Intended status: Standards Track | P. Patil |
| Expires: August 12, 2016 | M. Geller |
| Cisco | |
| M. Boucadair | |
| France Telecom | |
| R. Moskowitz | |
| HTT Consulting | |
| February 9, 2016 |
Co-operative DDoS Mitigation
draft-reddy-dots-transport-02
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 August 12, 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. The reader may refer, for example, to [REPORT] that reports the following:
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. 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, if a network resource detects a potential DDoS attack from a set of IP addresses, the network resource (DOTS client) informs its servicing router (DOTS relay) of all suspect IP addresses that need to be blocked or black-listed for further investigation. DOTS client could also specify protocols and ports in the black-list rule. That DOTS relay in-turn propagates the black-listed IP addresses to the DOTS server and the DOTS server blocks traffic from these IP addresses to the DOTS client thus reducing the effectiveness of the attack. The DOTS client periodically queries the DOTS server to check the counters mitigating the attack. If the DOTS client receives response that the counters have not incremented then it can instruct the black-list rules to be removed. If a blacklisted IPv4 address is shared by multiple subscribers then the side effect of applying the black-list rule will be that traffic from non-attackers will also be blocked by the access network.
If a DOTS client cannot determine the IP address(s) that are causing the attack, but is under an attack nonetheless, the DOTS client can just notify the DOTS server that it is under a potential attack and request that the DOTS server take precautionary measures to mitigate the attack.
If a DOTS server IPv4 path is working, but the DOTS server's IPv6 path is not working, a dual-stack DOTS client can experience significant connection delay compared to an IPv4-only DOTS client. The other problem is that if a middle box between the DOTS client and server is configured to block UDP, DOTS client will fail to establish DTLS session [RFC6347] with the DOTS server and will have to fall back to TLS over TCP [RFC5246] incurring significant connection delay. [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 MUST try connecting to the DOTS server using both IPv6 and IPv4, and MUST 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 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).
TBD: How does the DOTS client discover the DOTS server (use DNS-SD) ?
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 1: Happy Eyeballs
In the diagram above, the DOTS client sends two TCP SYNs and two DTLS ClientHello messages at the same time over IPv6 and IPv4. In the diagram, 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 delay to convey DOTS signal:
A DOTS client can use RESTful APIs discussed in this section to signal/inform a DOTS server of an attack or any desired IP filtering rules.
The following APIs define the means to convey an DOTS signal from a DOTS client to a DOTS server.
An HTTP POST request will be used to convey DOTS signal to the DOTS server.
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,
}
Figure 2: POST to convey DOTS signal
The header fields are described below.
Note: administrative-related clauses may be included as part of the request (such a contract Identifier or a customer identifier). Those clauses are out of scope of this document.
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.
The following example shows POST request to signal that a Web-Service is under attack.
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::1"},
"target-port": {"80", "8080", "443"},
"target-protocol": "tcp",
}
Figure 3: POST to signal SOS
The DOTS server indicates the result of processing the POST request using HTTP response codes. HTTP 2xx codes are success whereas HTTP 4xx codes are some sort of invalid request. 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 will be used to delete an DOTS signal signaled to the DOTS server. 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.
DELETE {scheme}://{host}:{port}/.well-known/{URI suffix for DOTS signal}
Accept: application/json
Content-type: application/json
{
"policy-id": number
}
Figure 4: Recall SOS
An HTTP GET request will be used to retrieve an DOTS signal signaled to the DOTS server. If the DOTS server does not find the policy number conveyed in the GET request in its policy state data then it responds with 404 HTTP error response code.
1) To retrieve all DOTS signal signaled by the DOTS client.
GET {scheme}://{host}:{port}/.well-known/{URI suffix for DOTS signal}
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}
Accept: application/json
Content-type: application/json
{
"policy-id": number
}
Figure 5: GET to retrieve the rules
The following example shows the response of all the active policies on the DOTS server.
{
"policy-data": [
{ "policy-id": 123321333242, "target-protocol": "tcp"},
{ "policy-id": 123321333244, "target-protocol": "udp"},
]
}
Figure 6: Response body
A DOTS client could use HTTPS to provision and manage filters on the DOTS server. The DOTS client authenticates itself to the DOTS relay, which in turn authenticates itself to a DOTS server, creating a two-link chain of transitive authentication between the DOTS client and the DOTS server. The DOTS relay validates if the DOTS client is authorized to signal the black-list rules. 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 HTTP proxy, validates the rules and proxies the HTTP requests containing the black-listed IP addresses to the DOTS server. When the DOTS relay receives the associated HTTP response from the HTTP 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 HTTP client and signal the black-list rules to the DOTS server. Thus the DOTS relay plays the role of both HTTP client and HTTP proxy.
Network Resource CPE router Access network (DOTS client) (DOTS relay) (DOTS server) __________ +-----------+ +----------+ +-------------+ / \ | |____| |_______| |___ | Internet | |HTTP Client| |HTTP Proxy| | HTTP Server | | | | | | | | | | | +-----------+ +----------+ +-------------+ \__________/
Figure 7
JSON [RFC7159] payloads can be used to convey both filtering rules as well as protocol-specific payload messages that convey request parameters and response information such as errors.
The figure above explains the protocol with a DOTS relay. The protocol is equally applicable to scenarios where a DOTS client directly talks to the DOTS server.
The following APIs define means for a DOTS client to configure filtering rules on a DOTS server.
An HTTP POST request will be used to push filtering rules to the DOTS server.
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 8: 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.
Note: administrative-related clauses may be included as part of the request (such a contract Identifier or a customer identifier). Those clauses are out of scope of this document.
The following example shows 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 provide HTTPS web service.
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": "1-65535",
"destination-protocol-port": "443",
"destination-ip": "2001:db8:abcd:3f01::/64",
"source-ip": "2002:db8:6401::1",
"lifetime": 1800,
"traffic-rate": 0,
}
Figure 9: POST to install black-list rules
An HTTP DELETE request will be used to delete filtering rules programmed on the DOTS server.
DELETE {scheme}://{host}:{port}/.well-known/{URI suffix for filtering}
Accept: application/json
Content-type: application/json
{
"policy-id": number
}
Figure 10: DELETE to remove the rules
An HTTP GET request will be used to retrieve filtering rules programmed on the DOTS server.
1) To retrieve all the black-lists rules programmed by the DOTS client.
GET {scheme}://{host}:{port}/.well-known/{URI suffix for filtering}
2) To retrieve specific black-list rules programmed by the DOTS cient.
GET {scheme}://{host}:{port}/.well-known/{URI suffix for filtering}
Accept: application/json
Content-type: application/json
{
"policy-id": number
}
Figure 11: GET to retrieve the rules
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 will 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 C. Jacquenet, Roland Dobbins, Andrew Mortensen, Roman D. Danyliw 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. |
| [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.