A broadcast (English for broadcasting) in a computer network is a message that is transmitted from one point in the data packets to all nodes of a network. In the switching technology, a broadcast is a special form of the multipoint connection.
A broadcast is mainly used in a computer network, if the address of the receiver of the message is still unknown. This technique is used (according to the OSI model) at the network layer to the application. An example of this are the protocols ARP and DHCP. Likewise, once an broadcast the simple transmission of information to all nodes of a network in order to, in contrast to unicast not transmitted the same information more than once must. If in this case, information is only sent to selected participants using multicast method.
Each recipient of a broadcast decides whether to process the message in the event of its jurisdiction or otherwise silently discards.
Network-capable computer games use broadcasts on the local network (not the Internet, here usually, a central server is used) to find a list of all open games in which the user can participate. When using the SMB protocol is also sought by broadcast to find printer and network shares on the local network.
Broadcasts, there are at various levels of the OSI reference model. What all have in common that broadcasts a higher level must be adjusted to the level of the physical network used. So, for example, has an IP broadcast on an Ethernet network as an Ethernet broadcast to the MAC address FF: FF: FF: FF: FF: FF be sent.
Is the underlying network does not broadcast capability, because it consists of a set of point-to -point connections, for example ( e.g., the Internet ), the network nodes need to be supplied by means of a flooding algorithm with the information.
Broadcasts in IPv4 are implemented via a group address. We distinguish between different forms of IP broadcasts:
Because of security issues with DoS attacks, the default behavior of routers in RFC 2644 has been modified for directed broadcasts. Routers should not forward directed broadcasts.
IPv6 does not support broadcasts more, it will be used instead multicasts.