In TCP or IP networking, what are the minimum and maximum header lengths (in bytes) for a TCP segment and an IPv4 datagram?

Introduction / Context:
Both TCP segments and IPv4 datagrams contain headers that carry control information such as addresses, sequence numbers, and flags. These headers consist of a fixed part plus optional fields. Knowing the minimum and maximum header lengths is important for understanding packet overhead, calculating maximum payload sizes, and analyzing protocol efficiency. This question asks for the correct minimum and maximum header lengths for both TCP and IPv4.

Given Data / Assumptions:

• The protocols in question are TCP at the transport layer and IPv4 at the network layer.
• Each header includes a field that indicates its length in units of 32 bit words.
• The minimum header length occurs when there are no options present.
• The maximum header length occurs when the options field is used to its full supported size.

Concept / Approach:
The TCP header has a minimum size of 20 bytes, which corresponds to five 32 bit words. This includes source and destination ports, sequence and acknowledgment numbers, flags, window size, checksum, and urgent pointer. The header length field allows for up to 15 32 bit words, which means a maximum header length of 60 bytes when options are used. The IPv4 header follows a similar pattern. Its minimum size is also 20 bytes when no options are present, and its header length field likewise allows for a maximum of 60 bytes with options. Therefore, both TCP and IPv4 share the same minimum and maximum header size range.

Step-by-Step Solution:
Step 1: Recall that the TCP header length is indicated in 32 bit words and that the minimum is five words.Step 2: Multiply five 32 bit words by 4 bytes per word to obtain a minimum size of 20 bytes for TCP.Step 3: Note that the TCP header length field can go up to 15 words, giving a maximum of 15 multiplied by 4 equal to 60 bytes when options are fully used.Step 4: Recall that the IPv4 header works similarly, with a header length field representing 32 bit words and a minimum of five words.Step 5: Conclude that the IPv4 header also has a minimum of 20 bytes and a maximum of 60 bytes when options are present, matching the correct option.

Verification / Alternative check:
Looking at protocol diagrams for TCP and IPv4, you can see the header length or Internet header length field. For TCP, reference documentation states that the minimum header is 20 bytes, and options up to 40 bytes may be added. For IPv4, the Internet header length field allows values from five to 15, corresponding to headers from 20 to 60 bytes. Packet analysis tools such as Wireshark also display header lengths that fall within this range, confirming these values in practical captures.

Why Other Options Are Wrong:
Option B is incorrect because 8 bytes is too small to hold even the fixed fields of either TCP or IPv4 headers. Option C is wrong because it gives inconsistent and incorrect ranges that do not match the specified word based header length fields. Option D is incorrect because 32 to 128 bytes is not supported by the standard header length encoding and would suggest much larger headers than actually defined by the protocols.

Common Pitfalls:
Students sometimes confuse the header size with the total maximum segment size or maximum transmission unit, which include payload data in addition to the header. Another pitfall is misreading the header length as bytes instead of 32 bit words in the protocol diagrams. Remembering that both TCP and IPv4 use 32 bit word units for header length and that the minimum is five words helps keep the 20 to 60 byte range clear in memory.

Final Answer:
The correct ranges are that the TCP header has a minimum length of 20 bytes and a maximum of 60 bytes, and the IPv4 header also has a minimum length of 20 bytes and a maximum of 60 bytes.