Network Port: 123
Network Port Reference Guide
Registered Service Name
NTP (Network Time Protocol)
Transport Protocol
UDP
Functional Overview
Port 123 is dedicated to the Network Time Protocol (NTP) to synchronize clock times across host devices over networks.
Security Risks & Vulnerabilities
Subject to NTP reflection and amplification distributed denial-of-service (DDoS) attacks. Ensure monlist querying is disabled.
How to audit network port status
1. Scan Open Ports: Use our Port Scanner utility to verify if this port is actively listening on your host.
2. Verify Encryption: Audit the service layer to confirm SSL/TLS is protecting transmission payload.
3. Hardening Rules: Apply the firewall instructions below to shut down unauthorized inbound ports.
UFW Firewall Rules
Allow Command
sudo ufw allow 123/udp
Block Command
sudo ufw deny 123/udp
iptables Firewall Rules
Allow Command
sudo iptables -A INPUT -p udp --dport 123 -j ACCEPT
Block Command
sudo iptables -A INPUT -p udp --dport 123 -j DROP