Glossary
Source Port
The source port is a 16-bit field in TCP and UDP headers that identifies the port number of the sender's application. It enables the receiver to know which application on the sender's host originated the packet, allowing for proper response routing.
Technical Details
Size
16 bits (2 bytes)
Range
0 – 65535
Well-known ports
0 – 1023 (requires privileged access)
Registered ports
1024 – 49151
Dynamic/Ephemeral ports
49152 – 65535
Protocols
TCP, UDP
Related Concepts
Port Binding
When a server application starts, it binds to a specific port number so incoming packets can be directed to the correct service.
NAT and Source Port Translation
Network Address Translators often modify the source port to allow multiple internal hosts to share a single public IP address.
Ephemeral Port Selection
Client applications typically use ephemeral ports (49152–65535) chosen by the operating system for outbound connections.
Used In Protocols
TCPUDP