The Network Time Protocol (NTP) synchronizes the time of day among a set of distributed time servers and clients
- NTP synchronizes time across devices so you can correlate system logs and other time-specific events from multiple network devices
- NTP uses UDP as its transport protocol
- An NTP server normally receives its time from an authoritative clock and distributes it across the network
- NTP is very efficient. 1 packet per second is all that is needed to synchronize a client within a millisecond of the server
- Stratum is used in NTP to describe the distance between a device and the time source
- Stratum1 = time source is directly attached
- Stratum2 = time is received from a Stratum1 source via NTP
- Before synchronizing, NTP compares the time reported by several network devices and does not synchronize with one that is significantly different, even if it is a stratum 1.
- Public NTP servers are available for use via the internet
- The time kept on a device is a critical resource. Use access list-based restrictions and an encrypted authentication mechanism to avoid the accidental or malicious setting of incorrect time.
- NTP server configuration:
Router#set clock 09:25:00 11 Dec 2018 Router#config t Router(config)#ntp master 2
- NTP client configuration:
Router#config t Router(config)#ntp server 10.0.0.2 Router(config)#ntp logging
- Optional - peers, access-lists, authentication...
Router(config)#ntp peer 192.168.0.10 Router(config)#ntp access-group peer peer-acl Router(config)#ntp access-group serve server-acl
PacketTracer Lab: CCNA-5.7-Configure-and-verify-NTP-operating-in-a-client-server-mode.pkt
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