Co-operative DDoS
MitigationCisco Systems, Inc.Cessna Business Park, Varthur HobliSarjapur Marathalli Outer Ring RoadBangaloreKarnataka560103Indiatireddy@cisco.comCisco Systems, Inc.170 West Tasman DriveSan JoseCalifornia95134USAdwing@cisco.comCisco Systems, Inc.praspati@cisco.comCisco Systems, Inc.3250Florida33309USAmgeller@cisco.comFrance TelecomRennes35000Francemohamed.boucadair@orange.comHTT ConsultingOak Park, MI42837United Statesrgm@htt-consult.comDOTSThis 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.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 that reports the
following:Very large DDoS attacks above the 100 Gbps threshold are
experienced.DDoS attacks against customers remain the number one operational
threat for service providers, with DDoS attacks against
infrastructures being the top concern for 2014.Over 60% of service providers are seeing increased demand for
DDoS detection and mitigation services from their customers (2014),
with just over one-third seeing the same demand as in 2013.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 certian
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.mortensen-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 .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 .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
notifiy the DOTS server that it is under a potential attack and request
that the DOTS server take precautionary measures to mitigate the
attack.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 signal an SOS from a DOTS
client to a DOTS server.TBD: SOS messages SHOULD be exchanged over DTLS over UDP.An HTTP POST request will be used to signal SOS to the DOTS
server.The header fields are described below.Identifier of the policy represented
using a number. This identifier must be unique for each policy
bound to the DOTS client. This identifier must be generated by
the client and used as an opaque value by the server. This
document does not make any assumption about how this identifier
is generated.A list of addresses or prefixes under
attack. This is an optional attribute.A list of ports under attack. This is
an optional attribute.A list of protocols under attack.
Valid protocol values include tcp, udp, sctp and dccp. This is
an optional attribute.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.To avoid SOS message fragmentation and the consequently decreased
probability of message delivery, DOTS agents MUST ensure that the
DTLS record MUST fit within a single datagram. DOTS agents can
exploit the fact that the IP specification specifies that IP packets up to 576 bytes
should never need to be fragmented, thus sending a maximum of 500
bytes of SOS message over a UDP datagram will generally avoid IP
fragmentation.The following example shows POST request to signal that a
Web-Service is under attack.An HTTP DELETE request will be used to delete an SOS signaled to
the DOTS server.An HTTP GET request will be used to retrieve an SOS signaled to
the DOTS server.A DOTS client could use HTTP 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.JSON 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.The header fields are described below.Identifier of the policy represented
using a number. This identifier must be unique for each policy
bound to the same downstream network. This identifier must be
generated by the client and used as an opaque value by the
server. This document does not make any assumption about how
this identifier is generated.Valid protocol values include
tcp and udp.For TCP or UDP or SCTP or
DCCP: the source range of ports (e.g., 1024-65535).For TCP or UDP or
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 .The destination IP addresses or
prefixes.The source IP addresses or
prefixes.Lifetime of the policy in seconds.
Indicates the validity of a rule. Upon the expiry of this
lifetime, and if the request is not reiterated, the rule will
be withdrawn at the upstream network. A null value is not
allowed.This field carries the rate
information in IEEE floating point [IEEE.754.1985] format,
units being bytes per second. A traffic-rate of '0' should
result on all traffic for the particular flow to be
discarded.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.An HTTP DELETE request will be used to delete filtering rules
programmed on the DOTS server.An HTTP GET request will be used to retrieve filtering rules
programmed on the DOTS server.TODOTODOHTTPS MUST be used for data confidentiality and (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 must be followed to avoid attacks on
(D)TLS.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 for the discussion and comments.Worldwide Infrastructure Security ReportBGP defines a mechanism as described in 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.