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Difficulty: MediumNTP Client and Server Operations and Configuration

An enterprise core router is designated to act as both an NTP client to an upstream stratum 2 server and an NTP server for internal distribution switches. To ensure reliable operations and consistent packet parameters, the network engineer must force the router to send NTP packets using a specific logical interface address and allow the router to serve as an authoritative time source if the upstream connection becomes unavailable. Which TWO Cisco IOS global configuration commands satisfy these requirements?

  1. ntp source Loopback0Answer
  2. ntp master 5Answer
  3. C
    ip helper-address 192.168.1.1
  4. D
    ntp server 127.127.1.1

Answer

The correct commands are 'ntp source Loopback0' and 'ntp master 5'.
Configuring 'ntp source Loopback0' ensures all outbound NTP control packets carry the loopback IP address as their source address, which aids access list matching and system stability. Configuring 'ntp master 5' allows the router to serve as a backup NTP server to downstream peers/clients at Stratum 5 when upstream synchronization fails.

Step-by-Step Solution

1
Identify the requirement for specifying the NTP packet source address.
The global configuration command 'ntp source <interface>' ensures NTP request/response packets use a stable IP address.
Loopback interfaces remain up as long as the router is powered, providing a consistent source IP for network management and security control.
2
Identify the requirement for providing fallback authoritative time synchronization.
The global configuration command 'ntp master [stratum]' enables the internal hardware clock to act as an NTP server.
Setting 'ntp master 5' allows downstream clients to synchronize with this device at stratum 5 if connection to the primary stratum 2 server is lost.

Key Concept

NTP Source Interface and Master Clock Fallback Configuration
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Topics

NTP Client and Server Operations and Configuration

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