Memcached is a high-performance, distributed memory object caching system used by a number of large Internet sites such as Wikipedia, Flickr, Twitter, and Youtube, as well as enterprise systems. Memcached is not designed for authentication and is protected only by firewalls and similar mechanisms.
The Search appliance runs the Memcached service to enable clustering. To secure Memcached, it is strongly recommended to deploy the Search appliance behind the firewall. Memcached service uses port 11211 and the firewall must allow this port for communication. For more information, see Ports Used in Filr Deployments in the Filr: Understanding How Filr Works.
For more information about Memcached, see Memcached.