200-901 · Question #231
Which protocol must be allowed on the firewall so that NTP services work properly?
The correct answer is C. UDP. NTP relies exclusively on UDP port 123 for time synchronization, so UDP must be permitted through the firewall for NTP to function.
Question
Which protocol must be allowed on the firewall so that NTP services work properly?
Options
- AICMP
- BBGP
- CUDP
- DTCP
How the community answered
(23 responses)- B9% (2)
- C87% (20)
- D4% (1)
Why each option
NTP relies exclusively on UDP port 123 for time synchronization, so UDP must be permitted through the firewall for NTP to function.
ICMP is used for network diagnostics and reachability testing such as ping, and has no role in NTP time synchronization.
BGP is a routing protocol used to exchange routing information between autonomous systems and is entirely unrelated to NTP time synchronization.
NTP (Network Time Protocol) uses UDP port 123 to exchange time synchronization packets between clients and servers. UDP is used because it is connectionless and adds minimal overhead, which is critical for accurate timestamping. Without UDP port 123 permitted on the firewall, NTP packets will be dropped and time synchronization will fail.
NTP does not use TCP; it uses connectionless UDP port 123, so permitting TCP would not enable NTP services.
Concept tested: NTP protocol transport and port requirements
Source: https://www.rfc-editor.org/rfc/rfc5905
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