Prepare for DDoS before availability becomes an incident

A large distributed denial-of-service attack can exceed controls at the target because the unwanted traffic has already consumed an upstream resource. Preparation therefore depends on service priorities, architecture, providers, communication, and rehearsed decisions—not only a firewall rule created during the outage.

Prepare with providers before the event

Source fact: CISA, FBI, and MS-ISAC recommend identifying critical externally available assets and services and reviewing the organizational impact of their loss. Organizations should understand DDoS protections and coverage gaps offered by internet, cloud, hosting, content-delivery, and mitigation providers before an attack.

Source fact: High availability, load balancing, colocation, and removal of single points of failure can improve continuity. The guidance also explains that large attacks may need to be stopped or diverted through upstream provider or specialized DDoS defenses before traffic reaches the local environment.

Source fact: A response plan should cover attack identification and confirmation, mitigation, monitoring, recovery, roles, communication, and provider coordination. Possible indicators include sudden traffic increases, latency, service unavailability, and degraded communications, but monitoring and traffic analysis are needed to distinguish an attack from other failures.

Build a service-specific playbook

DSE recommendation: rank each public service using safety, operational, financial, legal, customer, and reputational impact. Diagram its DNS, address space, protocols, authentication, application dependencies, provider paths, capacity, regions, failover, and single points of failure.

Record ISP, cloud, hosting, CDN, DNS, application, security-provider, leadership, communications, and law-enforcement contacts appropriate to the organization.

Document contracted protections, exclusions, protected addresses and protocols, activation method, authorization, expected telemetry, evidence needs, and support escalation.

Baseline normal traffic, latency, error, resource, and availability patterns and define criteria for confirmation and incident declaration.

Preapprove bounded filtering, rate limits, traffic diversion, scaling, alternate communication, and business-continuity options where technically appropriate.

Define evidence collection, status updates, recovery validation, and after-action review.

Exercise the real coordination path

DSE recommendation: run a tabletop with providers and a safe technical validation where contracts and architecture permit. Confirm who can activate mitigation, make DNS or routing changes, accept user impact, communicate externally, and declare recovery. Verify contacts outside the affected network and preserve configuration, traffic summaries, timestamps, alerts, logs, and provider records.

Applicability and limits

DDoS attacks vary by volume, protocol, reflection method, and application behavior. Rate limits or blocking can harm legitimate users, local capacity may not absorb an upstream attack, and a CDN may not cover every protocol or origin. The publication is general guidance, not a guarantee. Current provider architecture and contract terms determine available actions.

Official reference

Understanding and Responding to Distributed Denial-of-Service Attacks — joint preparedness and response guidance.