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Study Stuff for MCA Examinations - NIMCET
Study Stuff for MCA Examinations - NIMCET
Previous Year Question (PYQs)
Consider two hosts P and Q that are connected through a router R. The maximum transfer unit (MTU) value of the link between P and R is 1500 bytes and between R and Q is 820 bytes. A TCP segment of size 1400 bytes is transferred from P to Q through R with IP identification value of 0x1234. Assume that IP header size is 20 bytes. Further the packet is allowed to be fragmented, that is Don't fragment (DF) flag in the IP Header is not set by P. Which of the following statement/s is/are true?
A. Two fragments are created at R and IP datagram size carrying the second fragment is 620 bytes
B. If the second fragment is lost, then R resends the fragment with IP identification value of 0x1234
C. If the second fragment lost, then P requires to resend the entire TCP segment.
D. TCP destination port can be determined by analyzing the second fragment only.
Choose the correct answer from the options given below:
Solution
TCP segment size = 1400 bytes
IP header size = 20 bytes
MTU between R and Q = 820 bytes
Maximum data per fragment:
$820 - 20 = 800$ bytes
So fragments will be:
First fragment data = $800$ bytes
Second fragment data = $600$ bytes
Second IP datagram size:
$600 + 20 = 620$ bytes
So, A is true.
Router does not resend lost fragments, so B is false.
If a fragment is lost, source P retransmits the whole TCP segment, so C is true.
TCP header is present only in the first fragment, so destination port cannot be determined from the second fragment only. Hence D is false.
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