Multiplexing is the technique of carrying multiple independent data streams over a single network connection. In HTTP/2, this lets one client and server exchange many requests and responses at the same time without opening a separate connection for each request. The result is better efficiency, lower latency, and less overhead on the network.
In cyber security, multiplexing matters because the shared connection also means shared state. A server must track streams, flow control, and headers for each active conversation, which creates opportunities for resource exhaustion if limits are too loose. Attackers can abuse this by creating many streams or expensive connection patterns that consume memory, worker time, or proxy capacity, leading to denial of service. Defenders reduce this risk by setting strict limits on concurrent streams, request counts, and connection lifetimes, and by monitoring for abnormal HTTP/2 behavior at the edge.