Internet DRAFT - draft-zhang-dots-dns-considerations
draft-zhang-dots-dns-considerations
Internet Engineering Task Force H. Zhang
Internet-Draft P. Zuo
Intended status: Informational Y. Sun
Expires: January 27, 2021 M. Yuan
CNNIC
July 26, 2020
DNS DOTS considerations
draft-zhang-dots-dns-considerations-00
Abstract
DDoS Open Threat Signaling(DOTS) described in [RFC8612] is a
standardized method to coordinate a real-time response among involved
operators. This document focus on the considerations regard to the
use of DOTS to mitigate DNS-Related DDoS attacks.
Status of This Memo
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This Internet-Draft will expire on January 27, 2021.
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the Trust Legal Provisions and are provided without warranty as
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1. Introduction
Domain Name System(DNS) is one of the most foundational and essential
services on the Internet, the security and robustness of DNS are of
great significance. However, the stable operation of DNS has been
threatened by Distributate Denial of Service(DDoS) for quiet a long
time. In addition, DNS is often used to implement amplification
attacks, reflection attacks, etc.
DDoS Open Threat Signaling(DOTS) described in [RFC8612] is a
standardized method to coordinate a real-time response among involved
operators. This document focus on the considerations regard to the
use of DOTS to mitigate DNS-Related DDoS attacks.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document uses the terminologies defined in [RFC8612] and [I-
D.ietf-dots-use-cases].
3. DNS DOTS considerations
3.1. DOTS Server
DOTS Server described in RFC 8612 is responsible for handling
messages from DOTS client. In order to provide more effective and
comprehensive mitigation, the DOTS server should have the ability to
filter DNS messages based on different transfer protocols. At the
time of this writing, the majority of DNS traffic is transmitted in
plain text via UDP. As some new DNS protocols like DoT[RFC 7858],
DoH[RFC8484] are introduced, encrypted DNS traffic transmitted via
TLS and HTTPS is growing. As the normal deep packet inspection
method is not easy to detect encrypted traffic, port filtering or
deep learning methods can be considered to identify abnormal traffic
in the case of DoT or DoH.
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3.2. Filter
Filters described in RFC 8612 should be extended to filter DNS
traffic based on DNS message characteristics. For example, DNS
packets can be filtered by domain name queried. Based on the
telemetry of the attack, filter can drop or transmit DNS packages
according to specific domain names or other DNS characteristics. In
addition, filter should support bidirectional filtering of DNS
traffic. For example, for the use of DNS to implement amplification
attacks, the filter can drop the DNS response from the DNS server
side.
3.3. Data channel
Data channel described in RFC 8612 should support the transmission of
blacklists and whitelists used in DNS traffic filtering and DNS
service status between DOTS client and DOTS server. The list should
include the DNS packet characteristics such as IP, port, domain name,
query type, etc. For scenarios where the blacklist and whitelist
have huge size and may cost long time to transfer, regular and
incremental update should be considered to ensure timely delivery of
information.
3.4. Traffic Management
DNS server should deploy DNS traffic management module to detect DDoS
traffic. When DDoS attack happens, traffic management module will
notify DOTS client to request attack coordination with DOTS server.
3.4.1. threshold setting
DOTS Client should set dynamic thresholds for different attacks. For
example, Bit-and-piece attack is a new pattern of attach which
spreading small and fine-targeted traffic attacks across hundreds of
IP-addresses to evade detection. This new pattern is often leveraged
on open DNS resolvers to launch what is commonly known as DNS
amplification. In this case, a relatively low threshold should be
set to detect such attacks.
3.4.2. DNS traffic monitoring
The DNS server directly processes DNS traffic, thus it can obtain the
status of DNS nodes most accurately and timely. A suitable attack
detection system should be applied on the DNS server side to
implement attack detection, feature baseline learning, protection
strategy recommendations, etc. For example, the DOTS client deployed
in the DNS server side can comprehensively calculate the probability
of false alarm and the probability of missed reports to trigger the
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security mechanism reasonably. Attack detection system can consider
the classification of attack types, so that Filter can choose more
reasonable strategies in the early stage of a DDoS mitigation.
The DNS server should learn the characteristics of both the normal
DNS traffic and DDoS traffic in real time. The normal traffic
characteristics can be used as the normal flow profile. These
characteristics include but are not limited to: query rate of
specific domains, characteristics of domains, amplification ratio of
query size to response size, anomaly detection parameters and models
based on machine learning, etc.
Generally ordinary attacks have relatively obvious characteristics,
for example sending a large number of requests for random subdomains
to a DNS resolver. These type of attacks can be detected based on
the characteristics relatively simply. If the attack randomness is
strong and it is difficult to extract clear attack characteristics,
the characteristics aggregation can be performed by machine learning.
4. Example
Random subdomain attack is a type of DDOS against DNS service that
happens frequently. Attackers send a lot of DNS queries against a
valid and existing domain name. However, the queries will not target
the main domain name, but a lot of non-existing subdomains. The goal
of this attack is to create a DoS that will saturate the DNS server,
and cause the faliure of DNS service. Here is the mitigation process
of such Random subdomain attack.
1. A large number of requests for XXX.example.cn are mixed into the
normal DNS request, XXX represents a random domain name label. The
request traffic exceeds the service capabilities of DNS server.
2. The Traffic Moinitor located in DNS server detects the anomaly
traffic and sends attackrelated features and mitigation requests to
the Filter in the ISP through the DOTS interface. The information
contains the following: (1)The QNAME field of the attack packet is
random label + example.cn; (2)news.example.cn should be kept and
transmitted; (3)The normal QPS of domain name news.example.cn is M;
(4)The maximum response capacity of the server is N.
3: Filter implements mitigation process according to the signal it
receives and re-injects the cleaned data to the DNS server. After
filtering, the traffic contains normal request traffic and
news.example.cn requests. The total request traffic does not exceed
the DNS server service capacity.
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+---------DOTS signal/data channel-------+
|S C|
V |
+---------------------+ +------------+
| | | | | DDOS ATTACK | |
| | |Filter| |========================>|----------+ |
| | | | |========================>| DNS | |
| | +------+ |====|XXX.example.cn|====>| Traffic | |
| +-----------> |========================>| Detection| |
|------------------> |========================>|----------+ |
| +------------> | normal DNS traffic | |
| | +----------> |------------------------>| DNS |
| ISP | | | | Server |
+---------------------+ +------------+
*C is for DOTS client functionality
*S is for DOTS server functionality
Figure1: Random subdomain attack traffic
+--------DOTS signal/data channel--------+
|S C|
V |
+---------------------+ +------------+
| | |---+| |----------+ |
| |Filter|-+ || | DNS | |
| +------+ | || | Traffic | |
| ^ ^ | || news.example.cn | Detection| |
|----------- | | | +------------------------->|----------+ |
|------------+ | | | normal DNS REQ | |
| +--------+ +--------------------------->| |
| | +------ | | DNS |
| ISP | | | | Server |
+---------------------+ +------------+
*C is for DOTS client functionality
*S is for DOTS server functionality
Figure2: normal DNS traffic after filtering
In the above example, the Filter uses the characteristics of anomaly
traffic provided by the DNS serve. This process not only filters the
attack traffic, but also keeps normal DNS packets within the service
capabilities of the DNS server to the maximum extent.
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5. IANA Considerations
TBD.
6. References
[I-D.ietf-dots-use-cases]
Dobbins, R., Migault, D., Moskowitz, R., Teague, N., Xia,
L., and K. Nishizuka, ""Use cases for DDoS Open Threat
Signaling(work in progress)"", July 2019.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, ""Specification for DNS over Transport
Layer Security (TLS)"", May 2016,
<https://tools.ietf.org/html/rfc7858>.
[RFC8484] Hoffman, P. and P. McManus, ""DNS Queries over HTTPS
(DoH)"", October 2018,
<https://tools.ietf.org/html/rfc8484>.
[RFC8612] Mortensen, A., Reddy, T., and R. Moskowitz, ""DDoS Open
Threat Signaling (DOTS) Requirements"", May 2019,
<https://tools.ietf.org/html/rfc8612>.
Authors' Addresses
Haikuo Zhang
CNNIC
4 South 4th Street,Zhongguancun,Haidian District
Beijing, Beijing 100190
China
Phone: +86 10 5881 3163
Email: zhanghaikuo@cnnic.cn
Peng Zuo
CNNIC
4 South 4th Street,Zhongguancun,Haidian District
Beijing, Beijing 100190
China
Phone: +86 10 5881 2629
Email: zuopeng@cnnic.cn
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Yungang Sun
CNNIC
4 South 4th Street,Zhongguancun,Haidian District
Beijing, Beijing 100190
China
Phone: +86 10 5881 2669
Email: sunyungang@cnnic.cn
Meng Yuan
CNNIC
4 South 4th Street,Zhongguancun,Haidian District
Beijing, Beijing 100190
China
Phone: +86 10 5881 2669
Email: yuanmeng@cnnic.cn
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