Broadcast domain

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A network without VLANs or routers forms exactly one broadcast domain

A broadcast domain is a logical grouping of network devices in a local network , which is characterized by the fact that a broadcast reaches all domain participants.

A local network on the second layer of the OSI model ( data link layer ) consists of a broadcast domain through its hubs , switches and / or bridges . The broadcast domain is only divided up through the subdivision into VLANs or through the use of routers that work on layer 3.

A broadcast domain consists of one or more collision domains .


If a network subscriber wants to access his local router , he resolves its MAC address with ARP . The request is sent to the Ethernet broadcast address ff: ff: ff: ff: ff: ff. Switches forward all incoming Ethernet packets with the destination address ff: ff: ff: ff: ff: ff to all other ports. It must be ensured that there is no loop ( switching loop ) in the broadcast domain, otherwise a broadcast storm will occur .


The number of participants in a broadcast domain linearly loads the bandwidth of all connections in the broadcast domain. However, the bandwidth of the individual connections remains the same, regardless of the number of connections. From a certain number of participants, the broadcast traffic exceeds the useful traffic. To counteract this, the size of the broadcast domain must be reduced. Possible techniques:


  1. CCNA 3: Basics of Switching and Intermediate Routing 3.1.1 [1]
  2. BSI B 3.302 routers and switches [2]

See also