When it comes to networking and communication, there are many different ways network devices can talk to each other. Different processes utilize different communication types depending on the context. The most common message types are unicast, broadcast, multicast, and anycast. IPv4 utilizes unicast, broadcast, and multicast. IPv6 supports unicast, multicast, and anycast. IPv6 does not support broadcasting of any kind, as it uses multicast groups for functions that require broadcast in IPv4.
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Unicast- <\/strong>Unicast messages are a simple one to one communication. Unicast messages are mostly sent when the destination address is known, whether it’s an IP or MAC address. This message originates from one host and is only sent to one host. Think of the structure of an ethernet frame, or an IP packet even though they can be manipulated (via broadcast addresses) most of the time, it’s directed to only one host.\u00a0<\/p>\n\n\n\n Broadcast-<\/strong> Broadcast is a one-to-many type of communication. A broadcast message is confined within a LAN or broadcast domain, where if one host sends a message on the segment,\u00a0 every other connected host on that segment will receive that message whether they are interested in receiving it or not. Broadcast messages are a popular method for protocols such as ARP and DHCP (Discover and Request messages).\u00a0<\/p>\n\n\n\n Multicast- <\/strong>Multicast is a message sent to a specific group of interested receivers. Unlike broadcast where every device receives the message no matter what, multicast sends a message to multiple users at the same time but<\/em><\/strong> the receivers must be interested first. A device will show interest in receiving certain multicast messages by joining a multicast group. In multicast the sender transmits a single stream of data, meaning the data is transmitted once and is replicated at the routers to multiple receivers. Common forms of multicast today are IPTV, video conferencing for corporate meetings, routing updates, and financial market data. Dynamic protocols love multicast as a lot of them run on multicast such as OSPF, EIGRP, and RIPv2.\u00a0<\/p>\n\n\n\n Anycast- <\/strong>The final message type I will talk about is anycast which is mostly commonly configured on IPv6 enabled devices. This is a one-to-nearest kind of communication. In anycast multiple devices that are providing a service (Content Delivery Network, DNS Root Server) will be configured with the same IP addresses with the same prefix as well. Dynamic routing protocols are then responsible for providing these addresses to multiple locations with the same address and prefix. When devices (which are often clients) send traffic to these addresses the router will forward it to the server that is nearest according to the protocols metric. The hosts (typically PCs, phones, laptops) have no idea that they are being redirected to the closest server nor is it aware that multiple servers have the same IP address.<\/p>\n\n\n\n Further Reading Resources: <\/strong><\/p>\n\n\n\n