What is the difference between unicast, multicast, and broadcast?
Why Interviewers Ask This
Mid-level Networking roles require deep understanding of this topic. Interviewers ask this to separate candidates who truly understand the mechanics from those who only know surface-level concepts.
Answer
These are three methods of network communication based on the number of intended recipients. Unicast is one-to-one communication — a packet sent from a single source to a single specific destination. Most Internet traffic is unicast (HTTP, SSH, FTP). Broadcast is one-to-all — a packet sent to all devices in a network segment. ARP requests and DHCP Discovers use broadcast (IPv4 only — IPv6 eliminated broadcasts). Broadcasts are inefficient and can cause network performance issues if excessive. Multicast is one-to-many (or many-to-many) — a packet sent from one source to a group of interested receivers only. Uses multicast IP addresses (224.0.0.0–239.255.255.255 for IPv4). Efficient for streaming, video conferencing, and routing protocol updates (OSPF Hello packets use multicast 224.0.0.5). IGMP manages multicast group membership. Anycast (used in IPv6 and CDNs) sends to the nearest member of a group.
Common Mistake
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