CCNA 5.7: Configure and verify NTP operating in a client/server mode


The Network Time Protocol (NTP) synchronizes the time of day among a set of distributed time servers and clients

Study Notes:

  • 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
Router(config)#ntp logging
  • Optional - peers, access-lists, authentication...
Router(config)#ntp peer
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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