Cisco IOS Cookbook, 2nd Edition

Setting the Router As the NTP Master for the Network

Problem

You want to use the router as an NTP server to act as the primary time source for the network.

Solution

There is no need for a dedicated NTP server; you can pick one or two routers to act as authoritative NTP servers for the whole network. (The router should have a calendar function):

Router#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#clock timezone EST –5
Router(config)#clock summer-time EDT recurring
Router(config)#clock calendar-valid
Router(config)#ntp master 8
Router(config)#end
Router#

Discussion

When no authoritative time sources are available, and you still need to synchronize clocks throughout a network, you can configure a router to act as an NTP master server. Although this situation should be considered as a last resort, the router can become a “self-professed” NTP master, even if it is not actually synchronized from an accurate clock.

NTP provides two important services, accurate time setting and clock synchronization. Enabling a router to become a NTP master will not guarantee accurate time, but it will ensure that all network components’ time remain synchronized. This distinction is important because routers acting as NTP masters can synchronize their entire network to an incorrect time. However, if the reliable time sources that your network uses become unreachable for any length of time, it is often useful to at least keep the clocks synchronized, even if they ...