In network HA measurement, what is the meaning of five nines?

A) Five out of every nine networks fail.
B) Five out of every user's computers is unavailable for access.
C) The network should experience 99.999 percent uptime.
D) Five out of every nine network administrators are always available to take care of their network problem.

C
Explanation: The availability of a network is measured by its uptime during a year. For example, if a network has five nines of availability, it is up 99.999 percent of the time, which translates to a maximum of 5 minutes of downtime per year. If a network has six nines of availability (it is up 99.9999 percent of the time), it is down less than 30 seconds per year.