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A broadcast ( borrowed from English , for transmission , transmission , radio , broadcasting , here broadcast ) in a computer network is a message in which data packets are transmitted from one point to all participants in a communication network . In switching technology , a broadcast is a special form of multipoint connection .

A broadcast packet reaches all participants in a local network without explicitly specifying them as recipients. It follows that broadcasts should be limited to their own network segment and not be forwarded by routers . If information is to be sent to a group of selected participants, a multicast method is used instead .

Each recipient of a broadcast decides for himself whether, if he is responsible, he will either process the received message or otherwise silently discard it. There are broadcasts on different layers of the OSI reference model . What they all have in common is that broadcasts from a higher layer must be adapted accordingly to the lower layers. For example, an IPv4 broadcast is sent as an Ethernet broadcast to the MAC address FF:FF:FF:FF:FF:FF . If the underlying network is not broadcastable, for example because it - like the Internet, for example - consists of a number of point-to-point connections , the message can instead be sent using a flooding algorithm .


A broadcast is used in a computer network, among other things, when the IP address of the recipient of the message is still unknown. This technique is used in accordance with the OSI model in the network layer to the application. Examples are ARP , DHCP and Wake On LAN . Network-enabled computer games use broadcasts to find a list of all open games in the local network in which the user can participate. The SMB communication protocol searches for file and printer shares in the local network by broadcast .

IP broadcasts

Broadcasts in IPv4 are implemented via a group address. There are different types of IP broadcasts:

Limited broadcast
The IP address is as the destination . This goal is always in your own local network and is converted directly into an Ethernet broadcast. A router does not forward a limited broadcast .
Directed broadcast
The target are the participants of a particular network. The address is specified by the combination of the target network and the setting of all host bits to 1. The address for a directed broadcast into the network the network mask is thus: CIDR notation:) A directed broadcast is forwarded by a router if the source and destination network are different and is only converted into an Ethernet broadcast in the destination network. If the source and destination network are identical, this corresponds to a limited broadcast . This special case is often referred to as local broadcast . A directed broadcast can be viewed in a more differentiated manner. The broadcast can occur as subnet-directed broadcast , as all-subnets-directed broadcast or as net-directed broadcast . A subnet-directed broadcast has a specified subnet as its destination. An all-subnets-directed broadcast is a broadcast in all subnets of a network, and a net-directed broadcast is distributed in a classified network that is not divided into subnets (for example, broadcast to the address is in a class A distributed IP network).

Due to security problems with DoS attacks , the default behavior of routers in RFC 2644 for directed broadcasts has been changed. Routers should not forward directed broadcasts .

IPv6 no longer supports broadcasts; multicasts are used instead .

See also

Wiktionary: broadcast  - explanations of meanings, word origins, synonyms, translations

Web links

  • RFC 826 - Ethernet Address Resolution Protocol (English)
  • RFC 1812 - Requirements for IP Version 4 Routers (English)
  • RFC 2644 - Changing the Default for Directed Broadcasts in Routers

supporting documents

  1. broadcast - in the dictionary mentioned in ; there u. a. also with "Rundruf"