All ports
Port391/TCP
synotics-relayPort
391
Protocol
TCP
Category
Well-Known
Service
synotics-relay
What is port 391?
Port 391/TCP is a Well-Known port, assigned by IANA for widely recognized services. It is associated with the synotics-relay service.
SynOptics SNMP Relay Port
Useful commands
nmapnmap -p 391 -sV example.comnetcatnc -zv example.com 391curlcurl -v http://example.com:391/telnettelnet example.com 391bash(echo > /dev/tcp/example.com/391) 2>/dev/nullFirewall commands
UFWAllow
sudo ufw allow 391/tcpDeny
sudo ufw deny 391/tcpiptablesAllow
sudo iptables -A INPUT -p tcp --dport 391 -j ACCEPTDeny
sudo iptables -D INPUT -p tcp --dport 391 -j ACCEPTfirewalldAllow
sudo firewall-cmd --permanent --add-port=391/tcpWindowsAllow
netsh advfirewall firewall add rule name="Open Port 391" dir=in action=allow protocol=TCP localport=391Security 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- Outdated versions with vulnerabilities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 391/TCP?
Port 391/TCP is associated with the synotics-relay service. SynOptics SNMP Relay Port
Is it safe to expose port 391 to the Internet?
It depends on the service and configuration. Port 391 (synotics-relay) 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 391 is open?
You can use nmap: `nmap -p 391 -sV example.com`, netcat: `nc -zv example.com 391`, or the bash command: `(echo > /dev/tcp/example.com/391) 2>/dev/null && echo "Open" || echo "Closed"`.
How do I open or close port 391 on my firewall?
On Linux with UFW: `sudo ufw allow 391/tcp` (open) or `sudo ufw deny 391/tcp` (close). With iptables: `sudo iptables -A INPUT -p tcp --dport 391 -j ACCEPT`. On Windows: `netsh advfirewall firewall add rule name="Open Port 391" dir=in action=allow protocol=TCP localport=391`.
What applications and services use port 391?
Port 391/TCP is used by the synotics-relay service. Specific uses depend on the software and configuration. Check our related tools section for more information.