What is a port?¶

An IP address helps traffic reach a system. A port helps that system deliver the traffic to the right application or communication.

The short version¶

Think of an IP address as a building address and a port as a room or service entrance. One device can use the same IP while browsing, messaging and receiving updates because each communication has its own port information.

TCP and UDP ports range from 0 to 65535. A record may show:

source_ip: 192.0.2.44    source_port: 51514
destination_ip: 203.0.113.10  destination_port: 443
protocol: TCP

The destination port is where traffic is sent. The source port helps the sending system and return traffic keep the communication separate.

What a port can and cannot tell you¶

Port 443 is commonly used for HTTPS, 80 for HTTP and 53 for DNS. Those are conventions, not proof. Software can use another port, and a familiar port can carry an unexpected service.

A port does not identify a person or permanently identify a device. Source ports are often temporary and may be reused. Not all network protocols use TCP or UDP ports.