What Is Blackhole Routing? | How to Stop DDoS Attacks
Explore how blackhole routing works, when it is used to mitigate distributed denial-of-service (DDoS) attacks, and its trade-offs.
What Is Blackhole Routing?
Blackhole routing, sometimes called null routing, is a technique where network traffic to a specific IP address or range is intentionally dropped. Routers are configured to send that traffic to a "black hole"—an interface or route that discards packets instead of forwarding them.
From the outside, it looks as if the destination has gone offline. While this sounds severe, it can be an effective emergency measure during large-scale attacks.
Blackhole Routing During DDoS Attacks
During a major DDoS attack, the flood of malicious traffic can saturate links and overwhelm infrastructure, affecting not only the target but also nearby services. In such cases, network operators may use blackhole routing to sacrifice availability for the specific attacked target in order to preserve stability for the rest of the network.
Some internet service providers offer remote triggered blackhole (RTBH) services that allow customers to signal when specific addresses should be blackholed upstream, stopping traffic before it reaches the customer’s network.
Limitations and Alternatives to Blackhole Routing
The main drawback of blackhole routing is obvious: it effectively takes the targeted service offline, which is not acceptable as a long-term solution. It also provides no protection against attacks that target shared infrastructure or other parts of your environment.
More advanced DDoS mitigation strategies rely on traffic scrubbing centers, content delivery networks, and intelligent filtering that distinguish between legitimate and malicious traffic. Blackhole routing remains a valuable last resort for containing severe attacks, but it should be part of a broader incident response plan rather than the only line of defense.