ITPEC FE Morning October 2023 Question 34

Topic: Networks

Which of the following is a multicast IPv4 address?

Explanation

224.0.0.5 — its first octet, 224, lies in the class D range reserved for multicast.

IPv4 multicast addresses are 224.0.0.0 to 239.255.255.255 (224.0.0.0/4), that is, a first octet from 224 to 239. A packet sent to such an address goes to every host that has joined the group. 224.0.0.5 in particular is used by OSPF to reach all OSPF routers on a link.

Answer (d)

Why not others:

  • •(a) 10.1.1.1 — a private unicast address in 10.0.0.0/8
  • •(b) 192.0.2.0 — in 192.0.2.0/24, a unicast block reserved for documentation examples
  • •(c) 203.0.113.4 — in 203.0.113.0/24, another unicast block reserved for documentation

Key rule: Read the first octet: 1–126 class A, 128–191 class B, 192–223 class C, 224–239 class D multicast.

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