Internet UDP port 11211 is commonly used by the Memcached system, an open-source, high-performance distributed memory object caching system. Memcached is designed to speed up dynamic web applications by alleviating database load. It is also used by the Couchbase Server, a NoSQL cloud database. Other software may also use this port, but Memcached and Couchbase Server are the most notable examples.
UDP port 11211 is commonly associated with the Memcached distributed memory caching system. In the past, hackers have exploited this port for Distributed Denial of Service (DDoS) attacks, amplifying the impact by a factor of up to 51,000 times the original bandwidth. This was possible because Memcached servers, by default, had no authentication and were accessible to the public internet. Hackers would send a small packet of data to the vulnerable server, which would then respond with a much larger amount of data, overwhelming the target system. This type of attack, known as a Memcached DDoS attack, was notably used in 2018 to disrupt the services of GitHub, a popular web-based hosting service for version control. The attack generated a traffic load of 1.35 terabits per second, the largest ever recorded at the time.
