““The configuration in Example 33-8 works, but in many cases, routers might have multiple ntp server commands configured for redundancy. The goal is to have at least one usable clock source (servers per multiple ntp server commands, or internal clock as per the ntp master command). The router then chooses the best NTP clock source based on the stratum level. The stratum level defines the quality of the clock source; the lower the stratum, the better the source.””
