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200-901 · Question #231
200-901 Question #231: Real Exam Question with Answer & Explanation
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.
Network Fundamentals
Question
Which protocol must be allowed on the firewall so that NTP services work properly?
Options
- AICMP
- BBGP
- CUDP
- DTCP
Explanation
NTP relies exclusively on UDP port 123 for time synchronization, so UDP must be permitted through the firewall for NTP to function.
Common mistakes.
- A. ICMP is used for network diagnostics and reachability testing such as ping, and has no role in NTP time synchronization.
- B. BGP is a routing protocol used to exchange routing information between autonomous systems and is entirely unrelated to NTP time synchronization.
- D. 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
Reference. https://www.rfc-editor.org/rfc/rfc5905
Topics
#NTP#UDP#Firewall#Network protocols
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