Internet-Security.com UDP port 123 details

UDP port 123 is used by the Network Time Protocol (NTP) for clock synchronization.
Common software using it includes ntpd (NTP.org), chronyd (Chrony), OpenNTPD, and systemd-timesyncd on Linux/Unix.
Microsoft’s Windows Time Service (W32Time) uses UDP/123 to reach sources like time.windows.com.
Apple devices contact time.apple.com over UDP/123; Android devices use time.android.com/time.google.com; many routers/switches (Cisco IOS, Juniper Junos, MikroTik) run NTP on this port.
Public NTP services operating on UDP/123 include pool.ntp.org, Google Public NTP (time.google.com), Cloudflare (time.cloudflare.com), and NIST (time.nist.gov, ntp.time.gov).
Cloud/virtualization platforms use it too, e.g., AWS’s Amazon Time Sync Service at 169.254.169.123 and VMware ESXi hosts syncing to NTP servers.
Many enterprise appliances (e.g., Palo Alto PAN-OS, FortiGate, pfSense) provide NTP client/server features on UDP/123.
Security: exposed NTP servers on UDP/123 have been widely abused for reflection/amplification DDoS (e.g., the “monlist” issue, CVE-2013-5211), so restrict queries and disable legacy commands.

UDP 123