A-3. IP Port Numbers
Transport layer protocols identify higher-layer traffic with 16-bit fields called port numbers. A connection between two devices uses a source port and a destination port, both contained in the protocol data unit. Figure A-3 shows the User Data Protocol (UDP) header format, with the source and destination port fields shaded. Figure A-4 shows the Transmission Control Protocol (TCP) header format, with the source and destination port fields shaded.
Figure A-3. UDP Datagram Format Showing Port Fields
Figure A-4. TCP Segment Format Showing Port Fields
Both UDP and TCP use port numbers that are divided into the following ranges: ...
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