Type a port number or a service name to see what uses it, whether it should face the internet, and the commands to check or block it.
Examples:
Ports
41 of 41How to Use
A number such as 3389, or a name such as redis.
Each port says whether it belongs on the internet, behind an allow list, or never.
Each port has its own page with commands to check and block it.
IP & Network
A port number tells a server which program a connection is for: 443 for the web server, 22 for SSH, 3306 for MySQL. Ports 0 to 1023 are the well-known ports, assigned by IANA to standard services; 1024 to 49151 are registered ports; the rest are used for the client side of connections.
TCP and UDP have separate port numbers. DNS, for example, uses both TCP 53 and UDP 53.
Databases (3306, 5432, 27017, 6379), file sharing (445, 2049) and management protocols (161, 5900, 8006) should never face the internet. Exposed databases are found and attacked within hours.
Some UDP services are dangerous in a different way: open DNS resolvers, NTP, SSDP, CLDAP and memcached answer small spoofed requests with large replies, and attackers use them to flood third parties. Hosting providers get abuse reports for these even when the server owner did nothing wrong.
Ports
Free Tools
Frabs spots amplification, scans and floods leaving any VM and stops them, without touching your firewall.