Network Time Protocol (tcp/udp).
Quick facts
Description
Network Time Protocol (tcp/udp).
Well-known ports are assigned by IANA to system-level services; binding them usually requires administrative privileges.
Security notes
NTP. Used in reflection attacks; restrict queries to time-sync clients.
Related ports
What uses port 123?
Port 123 primarily carries the ntp service. Some common well-known ports include:
Port ranges
| Range | Explanation |
|---|---|
| Well-known (0–1023) | Reserved for system services; binding usually requires admin privileges. |
| Registered (1024–49151) | Available to user applications; IANA registers common services here. |
| Dynamic / private (49152–65535) | Used for ephemeral client connections. |
Frequently asked questions
A port number is a transport-layer address used independently by TCP and UDP; ntp typically runs over its documented transport protocol.
Yes — most services let you configure the listening port, but make sure clients and firewalls are updated and you avoid conflicts.
Sources & standards
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