GATE CS 2021 Set 1 — Question 55
Go beyond PYQs with Success TrackerAI-powered personalised practice and doubt support. Unlimited practice on eligible plans; AI usage limits apply.MSQ+2 / -0HardIPv4 Packet & FragmentationNetwork Layer: AddressingComputer Networks
Computer Networks → Network Layer: Addressing → IPv4 Packet & Fragmentation
Last updated
Question
Consider two hosts and connected through a router . The maximum transfer unit (MTU) value of the link between and is 1500 bytes, and between and is 820 bytes. A TCP segment of size 1400 bytes was transferred from to through , with IP identification value as 0x1234. 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 . Which of the following statements is/are correct?
Correct answer
(A) Two fragments are created at R and the IP datagram size carrying the second fragment is 620 bytes.; (C) If the second fragment is lost, P is required to resend the whole TCP segment.
Solution
1.Datagram Analysis:
- TCP segment size = 1400 bytes.
- IP header = 20 bytes.
- Total IP datagram size from to = bytes.
- MTU of link = 820 bytes.
- Maximum payload per fragment = bytes (which is a multiple of 8).
- Fragment 1: Payload = 800 bytes, Total size = 820 bytes, Offset = 0, MF = 1.
- Fragment 2: Payload = bytes, Total size = bytes, Offset = 100, MF = 0.
- Thus, (A) is correct.
- IP is an unreliable protocol; routers do not retransmit lost fragments. Thus, (B) is incorrect.
- If any fragment is lost, the destination cannot reassemble the datagram. TCP at the source () will eventually timeout and retransmit the entire original segment. Thus, (C) is correct.
- The TCP header (containing port numbers) is only present in the first fragment (offset 0). Subsequent fragments do not contain the TCP header. Thus, (D) is incorrect.
Continue learning with Success Tracker
A step still unclear? Work through it with support
Use Success Tracker to ask about the reasoning, then try another GATE CS question to check your understanding.
AI-powered practice· Unlimited practice on eligible plans
- PYQs with solutions
- Attempt available previous-year questions, then compare your reasoning with the worked solution. Coverage varies by stream.
- Practice that adapts
- Choose a topic, work on weaker areas and bookmark questions to revisit. Your attempts feed your progress tracking.
- AI doubt support
- Ask follow-up questions about a step or concept while practising, instead of stopping at the final answer.
Unlimited practice is available on eligible plans. Free practice and AI usage have limits; check the current plan allowances before choosing.
This page stays readable without an account. AI responses can be wrong; check them against the solution and source material.
More questions on Network Layer: Addressing
2026 Set 1 Q18With respect to a TCP connection between a client and a server, which one of the following…2026 Set 1 Q19Which of the following statements is/are true with respect to the interaction of a web browser with…2026 Set 2 Q21Consider a file of size 4 million bytes being transferred between two hosts connected via a path…2026 Set 2 Q22Which one of the following protocols may need to broadcast some of its messages?2026 Set 2 Q33If an IP network uses a subnet mask of 255.255.240.0, the maximum number of IP addresses that can…