In networking, "Casting" refers to how data is addressed to its destination. Depending on whether you're talking to one friend, a group, or everyone in the room, the protocol changes.
| Type | Scope | Main Use Case | Internet vs. Local |
|---|---|---|---|
| Unicast | 1-to-1 | General web browsing, HTTP, SSH. | Both |
| Broadcast | 1-to-All | ARP, DHCP, discovering local printers. | Local Only |
| Multicast | 1-to-Group | Live streaming, IPTV, video conferencing. | Both (but limited) |
| Anycast | 1-to-Closest | CDNs (Cloudflare), DNS (8.8.8.8), DDoS mitigation. | Internet Only |
Choosing the right method is about balancing Bandwidth and Reach. If you want to stream a 4K live event to 1 million people, Unicast would require 1 million individual streams (insane bandwidth). Multicast allows the network to handle the duplication, while Anycast ensures everyone connects to the server with the lowest ping.
Behind the Scenes: In IPv6, Broadcast has been removed entirely. It was considered too "noisy." Instead, IPv6 uses a specific Multicast group to achieve the same result more efficiently.