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Microsoft DDoS protection response guide

Receiving Distributed Denial of Service (DDoS) attack threats? This guide provides an overview of what Microsoft provides at the platform level, information on recent mitigations, and best practices.

Receiving Distributed Denial of Service (DDoS) attack threats?

DDoS threats have seen a significant rise in frequency lately, and Microsoft stopped numerous large-scale DDoS attacks last year. This guide provides an overview of what Microsoft provides at the platform level, information on recent mitigations, and best practices.

Microsoft DDoS platform

  • Microsoft provides robust protection against layer three (L3) and layer four (L4) DDoS attacks, which include TCP SYN, new connections, and UDP/ICMP/TCP floods.
  • Microsoft DDoS Protection utilizes Azure’s global deployment scale, is distributed in nature, and offers 60Tbps of global attack mitigation capacity.
  • All Microsoft services (including Microsoft365, Azure, and Xbox) are protected by platform level DDoS protection. Microsoft’s cloud services are intentionally built to support high loads, which help to protect against application-level DDoS attacks.
  • All Azure public endpoint VIPs (Virtual IP Address) are guarded at platform safe thresholds. The protection extends to traffic flows inbound from the internet, outbound to the internet, and from region to region.
  • Microsoft uses standard detection and mitigation techniques such as SYN cookies, rate limiting, and connection limits to protect against DDoS attacks. To support automated protections, a cross-workload DDoS incident response team identifies the roles and responsibilities across teams, the criteria for escalations, and the protocols for incident handling across affected teams.
  • Microsoft also takes a proactive approach to DDoS defense. Botnets are a common source of command and control for conducting DDoS attacks to amplify attacks and maintain anonymity. The Microsoft Digital Crimes Unit (DCU) focuses on identifying, investigating, and disrupting malware distribution and communications infrastructure to reduce the scale and impact of botnets.

Recent incidents1

At Microsoft, despite the evolving challenges in the cyber landscape, the Azure DDoS Protection team was able to successfully mitigate some of the largest DDoS attacks ever, both in Azure and in the course of history.

  • Last October 2021, Microsoft reported on a 2.4 terabit per second (Tbps) DDoS attack in Azure that we successfully mitigated. Since then, we have mitigated three larger attacks.
  • In November 2021, Microsoft mitigated a DDoS attack with a throughput of 3.47 Tbps and a packet rate of 340 million packets per second (pps), targeting an Azure customer in Asia. As of February 2022, this is believed to be the largest attack ever reported in history. It was a distributed attack originating from approximately 10,000 sources and from multiple countries across the globe, including the United States, China, South Korea, Russia, Thailand, India, Vietnam, Iran, Indonesia, and Taiwan.

Protect your applications in Azure against DDoS attacks in three steps:

Customers can protect their Azure workloads by onboarding to Azure DDoS Protection Standard. For web workloads it is recommended to use web application firewall in conjunction with DDoS Protection Standard for extensive L3-L7 protection.

1. Evaluate risks for your Azure applications. This is the time to understand the scope of your risk from a DDoS attack if you haven’t done so already.

a. If there are virtual networks with applications exposed over the public internet, we strongly recommend enabling DDoS Protection on those virtual networks. Resources in a virtual network that requires protection against DDoS attacks are Azure Application Gateway and Azure Web Application Firewall (WAF), Azure Load Balancer, virtual machines, Bastion, Kubernetes, and Azure Firewall. Review “DDoS Protection reference architectures” to get more details on reference architectures to protect resources in virtual networks against DDoS attacks.

Enabling DDOS Protection Standard on a VNET

2. Validate your assumptions. Planning and preparation are crucial to understanding how a system will perform during a DDoS attack. You should be proactive to defend against DDoS attacks and not wait for an attack to happen and then act.

a. It is essential that you understand the normal behavior of an application and prepare to act if the application is not behaving as expected during a DDoS attack. Have monitors configured for your business-critical applications that mimic client behavior and notify you when relevant anomalies are detected. Refer to monitoring and diagnostics best practices to gain insights on the health of your application.

b. Azure Application Insights is an extensible application performance management (APM) service for web developers on multiple platforms. Use Application Insights to monitor your live web application. It automatically detects performance anomalies. It includes analytics tools to help you diagnose issues and to understand what users do with your app. It’s designed to help you continuously improve performance and usability.

c. Finally, test your assumptions about how your services will respond to an attack by generating traffic against your applications to simulate DDoS attack. Don’t wait for an actual attack to happen! We have partnered with Ixia, a Keysight company, to provide a self-service traffic generator (BreakingPoint Cloud) that allows Azure DDoS Protection customers to simulate DDoS test traffic against their Azure public endpoints.

3. Configure alerts and attack analytics. Azure DDoS Protection identifies and mitigates DDoS attacks without any user intervention.

a. To get notified when there’s an active mitigation for a protected public IP, we recommend configuring an alert on the metric under DDoS attack or not. DDoS attack mitigation alerts are automatically sent to Microsoft Defender for Cloud.

b. You should also configure attack analytics to understand the scale of the attack, traffic being dropped, and other details.

DDOS attack analytics

Best practices to be followed

  • Provision enough service capacity and enable auto-scaling to absorb the initial burst of a DDoS attack.
  • Reduce attack surfaces; reevaluate the public endpoints and decide whether they need to be publicly accessible.
  • If applicable, configure Network Security Group to further lock-down surfaces.
  • If IIS (Internet Information Services) is used, leverage IIS Dynamic IP Address Restrictions to control traffic from malicious IPs.
  • Setup monitoring and alerting if you have not done so already.
    Some of the counters to monitor:

    • TCP connection established
    • Web current connections
    • Web connection attempts
  • Optionally, use third-party security offerings, such as web application firewalls or inline virtual appliances, from the Azure Marketplace for additional L7 protection that is not covered via Azure DDoS Protection and Azure WAF (Azure Web Application Firewall).

When to contact Microsoft support

  • During a DDoS attack if you find that the performance of the protected resource is severely degraded, or the resource is not available. Review step two above on configuring monitors to detect resource availability and performance issues.
  • You think your resource is under DDoS attack, but DDoS Protection service is not mitigating the attack effectively.
  • You’re planning a viral event that will significantly increase your network traffic.

For attacks that have a critical business impact, create a severity-A support ticket to engage DDoS Rapid Response team.


1Azure DDoS Protection—2021 Q3 and Q4 DDoS attack trends