What is the result of the NTP master configuration?
Short answer
D The router will be used as an NTP authoritative server, even if it is not synchronized with an outside source.
Question
Key Takeaways
The 'ntp master' command configures the router as an authoritative NTP server regardless of external synchronization, which is commonly confused with requiring an upstream time source.
The question tests the behavior of the 'ntp master' command in Cisco IOS, specifically whether the router acts as an authoritative NTP server without external synchronization. Community consensus strongly supports answer D, confirming that 'ntp master' allows the router to serve as an authoritative time source even without an external reference.
Common mistake: Many candidates choose C, incorrectly believing that the router will only act as an authoritative NTP server if it is synchronized with an outside source, confusing 'ntp master' with standard NTP client behavior.
Expert Analysis
Why the Answer Is Correct
The ntp master command explicitly configures the router to act as an authoritative NTP server (stratum 8 by default) even when it is not synchronized to any external time source. This is designed for isolated networks where no external reference clock is available. The ntp source loopback0 simply dictates the source IP for outgoing NTP packets but does not affect the master behavior. Therefore, the router will serve time authoritatively regardless of external sync status.
Why the Other Options Are Wrong
Option A is partially true regarding the source interface but does not describe the primary result of the ntp master configuration shown. Option B describes NTP broadcast mode (ntp broadcast), which is not configured here. Option C incorrectly states that external synchronization is required; this contradicts the fundamental purpose of ntp master, which is to provide time when no external source exists.
Community Comment Notes
Comments [1] and [2] correctly explain that ntp master allows the router to act as an authoritative server without an external clock, aligning with Cisco documentation. Comments [3] and [4] incorrectly argue for C, highlighting the common misconception that an external source is mandatory. The high vote count for D (100 votes) reinforces community agreement on the correct answer.
Official Reference
This link opens the official vendor documentation in a new tab.
Exam Strategy
When you see 'ntp master' in a Cisco exam, remember it forces the router to act as an authoritative NTP server regardless of external synchronization. Do not confuse this with normal NTP client behavior that requires an upstream source.
Community Votes
100% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.
Discussion 3 contributions
Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.
From public community threads 3
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Mistwalker 👍 2 Answered Dhttps://www.cisco.com/c/en/us/td/docs/ios-xml/ios/bsm/command/bsm-cr-book/bsm-cr-n1.html#wp1522568655 Because the Cisco implementation of NTP does not support directly attached radio or atomic clocks, the router is normally synchronized, directly or indirectly, to an external system that has such a clock. In a network without Internet connectivity, such a time source may not be available. The ntp master command is used in such cases. To configure the Cisco IOS software as a Network Time Protocol (NTP) master clock to which peers synchronize themselves when an external NTP source is not available, use the ntp master command in global configuration mode.
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chiacche 👍 1 Answered Dntp master -> act as an authoritative NTP server. ntp source lookback0 -> tells the router to use its loopback 0 interface as the source IP address for NTP communications.
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supershysherlock 👍 1 Answered DCorrect
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