Internet-Security.com UDP port 11211 details

UDP port 11211 is primarily used by Memcached, the distributed in-memory caching system; the memcached daemon listens on 11211 for both TCP and UDP by default.
Real-world deployments include large-scale users of Memcached such as Facebook and Wikimedia, as well as many web stacks via libmemcached and language clients (PHP, Python, Ruby).
Twemcache (Twitter’s fork of Memcached) also speaks the Memcached protocol and can use UDP/TCP on port 11211 in compatible setups.
This port is associated with exploitation: exposed Memcached UDP services have been widely abused for reflection/amplification DDoS attacks (notably in 2018), so many operators disable UDP or firewall UDP/11211.

UDP 11211