GATE CS 2025 Set 2 | Question 18

MCQ · 1 mark · −0.33

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?

  1. Option A: Internet Control Message Protocol (ICMP)
  2. Option B: Internet Group Management Protocol (IGMP)
  3. Option C: Open Shortest Path First (OSPF)
  4. Option D: Routing Information Protocol (RIP) (correct)

Answer

(D)

Explanation

The protocol field names the protocol whose message sits directly in the payload of the IP datagram, so X must be a protocol that runs immediately on top of IP.

  • ICMP (protocol number 1) and IGMP (2) are carried directly in IP datagrams.
  • OSPF also runs directly over IP, with protocol number 89.
  • RIP does not. Its messages travel inside UDP datagrams on port 520, so a datagram carrying RIP has 17 (UDP) in its protocol field, and RIP is identified only by the UDP port.

So RIP cannot be X.

Answer: D