GATE CS 2020 Set 1 — Question 25

MCQ+1 / -0.33MediumNetwork Layer: RoutingComputer NetworksIPv4 Packet & FragmentationNetwork Layer: Addressing

Computer Networks → Network Layer: Addressing → IPv4 Packet & Fragmentation

Last updated 5 September 2026

Question

Consider the following statements about the functionality of an IP based router. I. A router does not modify the IP packets during forwarding. II. It is not necessary for a router to implement any routing protocol. III. A router should reassemble IP fragments if the MTU of the outgoing link is larger than the size of the incoming IP packet. Which of the above statements is/are TRUE?

Correct answer (D) II only Solution Let's analyze the statements: I. False . A router modifies the IP header. Specifically, it decrements the TTL (Time To Live) field and recomputes the Header Checksum before forwarding the packet. II. True . While routing protocols (like OSPF, BGP) are commonly used to populate routing tables dynamically, they are not strictly necessary. A router can function using only static routing entries configured manually by an administrator. III. False . Routers generally do not reassemble IP fragments. Reassembly is typically performed only at the destination host. If an outgoing link has a smaller MTU, a router may fragment a packet further, but it does not reassemble fragments just because the outgoing MTU is larger. Thus, only statement II is true. Turn this into a strength. Explore AI-powered practice and doubt support with Success Tracker.

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Correct answer (D) II only Solution Let's analyze the statements: I. False . A router modifies the IP header. Specifically, it decrements the TTL (Time To Live) field and recomputes the Header Checksum before forwarding the packet. II. True . While routing protocols (like OSPF, BGP) are commonly used to populate routing tables dynamically, they are not strictly necessary. A router can function using only static routing entries configured manually by an administrator. III. False . Routers generally do not reassemble IP fragments. Reassembly is typically performed only at the destination host. If an outgoing link has a smaller MTU, a router may fragment a packet further, but it does not reassemble fragments just because the outgoing MTU is larger. Thus, only statement II is true.

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