All ports
Port123/UDP
ntpPort
123
Protocol
UDP
Category
Well-Known
Service
ntp
What is port 123?
Port 123/UDP is a Well-Known port, assigned by IANA for widely recognized services. It is associated with the ntp service.
Network Time Protocol
Useful commands
nmapnmap -p 123 -sV example.comnetcatnc -zv example.com 123curlcurl -v http://example.com:123/telnettelnet example.com 123bash(echo > /dev/udp/example.com/123) 2>/dev/nullFirewall commands
UFWAllow
sudo ufw allow 123/udpDeny
sudo ufw deny 123/udpiptablesAllow
sudo iptables -A INPUT -p udp --dport 123 -j ACCEPTDeny
sudo iptables -D INPUT -p udp --dport 123 -j ACCEPTfirewalldAllow
sudo firewall-cmd --permanent --add-port=123/udpWindowsAllow
netsh advfirewall firewall add rule name="Open Port 123" dir=in action=allow protocol=UDP localport=123Security Risks
- Unauthorized access to the service
- Data exposure if the service is unauthenticated
- Outdated versions with vulnerabilities
- Incorrect service configuration
Frequently Asked Questions
What service runs on port 123/UDP?
Port 123/UDP is associated with the ntp service. Network Time Protocol
Is it safe to expose port 123 to the Internet?
It depends on the service and configuration. Port 123 (ntp) is a Well-Known port. If you need to expose it, keep the service updated, use strong authentication, and configure a firewall. It's always recommended to restrict access by IP when possible.
How do I check if port 123 is open?
You can use nmap: `nmap -p 123 -sV example.com`, netcat: `nc -zv example.com 123`, or the bash command: `(echo > /dev/udp/example.com/123) 2>/dev/null && echo "Open" || echo "Closed"`.
How do I open or close port 123 on my firewall?
On Linux with UFW: `sudo ufw allow 123/udp` (open) or `sudo ufw deny 123/udp` (close). With iptables: `sudo iptables -A INPUT -p udp --dport 123 -j ACCEPT`. On Windows: `netsh advfirewall firewall add rule name="Open Port 123" dir=in action=allow protocol=UDP localport=123`.
What applications and services use port 123?
Port 123/UDP is used by the ntp service. Specific uses depend on the software and configuration. Check our related tools section for more information.