Transport layer protocols identify higher-layer traffic with 16-bit fields called port numbers. A connection between two devices uses a source and a destination port, both contained within the protocol data unit. Figure G-1 shows the User Datagram Protocol (UDP) header format, with the source and destination port fields shaded. Figure G-2 shows the Transmission Control Protocol (TCP) header format, with the source and destination port fields shaded.
Figure G-1. UDP Datagram Format Showing Port Fields
Figure G-2. TCP Segment Format Showing Port Fields
Both UDP and TCP port numbers are divided into the ...