GATE CSE 2025 Session 2 Q18: Protocol that cannot appear in the IPv4 protocol field

A machine receives an IPv4 datagram. The protocol field of the IPv4 header has the protocol number of a protocol X.

Which ONE of the following is NOT a possible candidate for X?

Try it: multiple choice: exactly one correct option

Wrong answer costs 1/3 mark in GATE.

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Answer: D (official GATE 2025 final answer key)

Concept used: The IPv4 protocol field names the protocol carried directly inside IP.

First step: ICMP, IGMP and OSPF ride directly on IP; check what RIP is carried in (UDP port 520).

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Source: official GATE 2025 Session 2 CS question paper and final answer key, organised by IIT Roorkee. Question paper · Answer key