TCP Source Port Number Size in Bits
How many bits is Source Port Number in TCP Header packet?
Community Votes
100% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
This question tests knowledge of TCP header structure fields and their bit lengths, specifically identifying the fixed 16-bit size of the source port identifier.
The TCP header's source port number field is exactly 16 bits long, a fundamental constant of the TCP/IP protocol suite defined in RFC 793. This page confirms that option A is the correct answer based on standard network architecture.
Learners sometimes confuse the 16-bit port number with the 32-bit sequence numbers or IP addresses, but the port field is strictly limited to 16 bits to support 65,536 ports per endpoint.
Community Discussion (3 comments)
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Expert Analysis
Why the Answer Is Correct
The Transmission Control Protocol (TCP) header contains a 16-bit source port field. This field is used by the source host to identify the specific application or process initiating the connection. Because it is 16 bits wide, it allows for values ranging from 0 to 65,535, which defines the range of available ports.Why the Other Options Are Wrong
Option B (32) refers to fields like the Sequence Number or Acknowledgment Number, not the port. Option C (48) typically corresponds to MAC addresses (Layer 2), while Option D (64) does not correspond to any standard single-field size in the basic TCP header.Community Comment Notes
The community consensus strongly supports option A, citing RFC 793 as the authoritative source. Comments clarify that the 16-bit size is a fixed part of the protocol specification, distinguishing it from other header fields that may be 32 bits.Official Reference
Exam Strategy
Memorize the key bit-lengths of the TCP header: Source/Dest Ports are 16 bits each, Sequence/Ack Numbers are 32 bits each. Understanding these fixed sizes helps you quickly eliminate distractors in network forensics questions.
Frequently Asked Questions
Why is the source port 16 bits instead of 32?
16 bits allow for 65,536 unique ports, which is sufficient for most applications without wasting header space.
Does the destination port also use 16 bits?
Yes, both the source and destination port fields in the TCP header are 16 bits each.