Networking
Risk: Low
Port 123 — NTP (Network Time Protocol)
Port 123 is the fundamental UDP port for NTP and chrony, synchronizing system clocks across computer networks down to millisecond precision.
PORT NUMBER
123
PROTOCOL
UDP
DEFAULT PROCESS
ntpd, chronyd, systemd-timesyncd
FIREWALL TARGET
123/udp
Instant Terminal Fixes for Port 123
macOS & Linux Terminal
1. Check who is listening on port 123:
chronyc tracking || sudo ss -ulpn | grep ":123 "2. Kill process occupying port 123 (EADDRINUSE fix):
sudo systemctl stop chronyd || sudo systemctl stop ntp3. UFW Firewall Allow rule:
sudo ufw allow 123/udpWindows PowerShell (Admin)
1. Check listening port:
w32tm /query /status2. Force kill process on port 123:
Stop-Service W32Time -Force3. Docker Port Forwarding Mapping:
docker run -d -p 123:123/udp --cap-add=SYS_TIME cturra/ntpCommon Error Encountered
ntpdate: no server suitable for synchronization found on port 123.
Security Advisory & Hardening
Older NTP daemon versions are vulnerable to NTP amplification DDoS attacks (monlist). Ensure NTP monlist is disabled in ntp.conf.
Frequently Asked Questions
Port 123 Questions & Answers
Common questions regarding default services, kill commands, and firewall configurations.
Port 123 is commonly used for NTP (Network Time Protocol). Port 123 is the fundamental UDP port for NTP and chrony, synchronizing system clocks across computer networks down to millisecond precision.