Broadcast on a network means one node transmits packets to all other nodes in the same domain simultaneously. Multicast is a special form of broadcast, in which a selected group of users who requested to listen to the broadcast will receive the broadcasts. Broadcast transmission is supported on most LANs (e.g. Ethernet). Broadcast can also happen in a virtual LAN (VLAN). IPv6 has unicast, multicast, and anycast. Broadcast has disappeared as a term, but is considered one form of multicast.
There are a few key concepts in the broadcast over network:
Broadcast domain: it is a restricted area in which information is shared by all devices. In other words, all the devices attached to the network that receive the broadcast are part of the same broadcast domain. In a shared Ethernet, stations broadcast frames to all other nodes through a shared medium. Other nodes listen to the broadcasts but only receive the frames addressed to them. Therefore, all nodes in a shared Ethernet belong to the same broadcast domain. Virtual LAN technology can create a virtual broadcast domain.
Broadcast address: This is a special address for all devices to open and process the message if a packet is addressed to this address. For example, the MAC address with all 1s (1xFFFFFFFF) is a broadcast address and the IP address 255.255.255.255 is the general broadcast address. Any device sees a message addressed to the broadcast address shall open it and then pass the message to the next station.
Broadcast storm: If a broadcast packet circulating on the network continuously and many systems reply to it, or a system keeps its effort to another system that never replies, a broadcast storm will happen. A broadcast storm may cause congestion of the network as the number of packets on the network increases. Broadcast storms can usually be prevented by carefully configuring a network to block illegal broadcast messages.
Applications that produce broadcast messages include Address Resolution Protocol (ARP). It is used by hosts to locate IP addresses on a network by sending an address resolution query to all computers on a LAN. Some routing protocols such as RIP is for network device to "advertise" their services on the network. There are also many technologies related to multicasting, a special form of broadcasting and the details of multicasting can be found in the multicasting section. Technologies related to virtual LAN can be found in the VLAN section.
Related Terms: Multicast, VLAN, ARP, RIP, Broadcast domain, Broadcast address, Broadcast storm