Log monitoring tools performing behavioral analysis have alerted several suspicious logins on a Linux server occuring during non-business hours. After further examination of all login activities, it…

Log monitoring tools performing behavioral analysis have alerted several suspicious logins on a Linux server occuring during non-business hours. After further examination of all login activities, it is notices that none of the logins have occurred during typical work hours. A Linux administrator who is investigating this problem realized the system time on the Linux server is wrong by more than twelve hours. What protocol used on Linux serves to synchronize the time has stopped working?