Strong authentication can also risk availability. A simple example is that forgetting your password denies you access to that which required a password. Sometimes the stakes are high, for example, if a network administrator is the only one who knows the password to (or holds the only token for access to) a network device needed to block an ongoing attack. Even network administrators get sick, have accidents, are unreachable, or lose things. This situation is known as a single point of failure because the ability to access depends on one critical link: the administrator. How can a company prevent such a single point of failure? suppose access is controlled by a biometric. How could the person's absence be dealt with ?