Broadcasting is a term used by radio and television media. The basic concept is the transmission of a signal that everyone can receive. The same concept exists in computer networks. In this case, a computer or network device sends a signal out that every other device on the network receives.
Here are two examples:
Example one – A new computer starts up. It is connected to the network but needs an IP address. It then sends a broadcast asking any DHCP server for an IP. It cannot send a direct request to the DHCP server, as it does not know if one exists. When a DHCP server gets the broadcast packet, it will reply with an IP address.
Example two – To provide access to a file share, or access other file shares, a computer needs a list of all other computers on the network. The only way it gets this list is by sending out a broadcast to locate other computers.
The broadcast on a computer network is different from other network traffic. The broadcast is sent to a specific MAC address – FF:FF:FF:FF:FF:FF:. Every device on a network understands that it is a broadcast and replies if relevant or drops it in other cases.
However, there is a downside. On a small network, the amount of broadcast traffic is negligible. On a larger network, like a campus with 20,000+ devices, the broadcast traffic can consume a large chunk of available network bandwidth. This is where VLANs and other network technologies come in.