Key chains are an important part of the Routing Information Protocol (RIP) and Enhanced Interior Gateway Routing Protocol (EIGRP) whereby a routers' security is ensured within a network. A key chain is a series of keys that the network administrator assigns to the routers that are repeated by the routers' software in rotation. Each key has its own "life span" during which it is active and accepted between any two routers before communication takes place. "Key string" is the name given to the authentication code constituting a key chain.