Here's the question bank on all the computer networks topics.
Consider two hosts P and Q 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 was transferred from P to Q through R, with IP identification value as 0 × 1234. Assume that the IP header size is 20 bytes. Further, the packet is allowed to be fragmented i. e, Don't Fragment (DF) flag in the IP header is not set by P.Which of the following statements is/are correct?
Answer: Option 2 and Option 3Explanation:TCP Segment Size = 1400Packet size = segment size + IP Header Size = 1400+ 20 = 1420 At R Packet will be Fragmented MTU = 800 + 20 (Header) Hence Packet's Data (1400) will be divided in two packets = (800 + 600)First Fragment = (800 + 20) //Data + HeaderSecond Fragment = ( 600 + 20 ) Option 1: The TCP destination port can be determined by analyzing only the second fragment.This Option is not correct as Destination Port Number can be identified by looking at any packet or Fragment. not just only from Second Fragment.Option 2:If the second fragment is lost, P is required to resend the whole TCP segment.This is correct. If any of the Fragments is lost then the entire packet/TCP segment has to be retransmitted this one of the drawbacks of fragmentation.Option 3:Two fragments are created at R and the IP datagram size carrying the second fragment is 620 bytes.This is correct.Option 4: If the second fragment is lost, R will resend the fragment with the IP identification value 0 × 1234.This Option is not correct As If any of the Fragments is lost then the entire packet/TCP segment has to be retransmitted.
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