N10-005 · Question #845
Which of the following ports would have to be allowed through a firewall for NTP to pass on its default port?
The correct answer is A. 123. NTP uses UDP port 123 by default, and firewalls must permit this port for time synchronization traffic to pass.
Question
Which of the following ports would have to be allowed through a firewall for NTP to pass on its default port?
Options
- A123
- B143
- C153
- D163
How the community answered
(37 responses)- A89% (33)
- B5% (2)
- C3% (1)
- D3% (1)
Why each option
NTP uses UDP port 123 by default, and firewalls must permit this port for time synchronization traffic to pass.
Network Time Protocol (NTP) is assigned UDP port 123 by IANA as its well-known port for both client requests and server responses. Any firewall policy that needs to allow NTP time synchronization - whether to an internal NTP server or an external time source - must include a rule permitting UDP port 123 in the relevant direction.
Port 143 is assigned to IMAP (Internet Message Access Protocol), used for retrieving email from a mail server.
Port 153 is not associated with a commonly used standard protocol and is not related to NTP.
Port 163 is associated with CMIP (Common Management Information Protocol) and is unrelated to time synchronization.
Concept tested: NTP default port number for firewall configuration
Source: https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml
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