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In a Layer 2 network, broadcasting refers to sending traffic to all nodes on a network.
Layer 2 broadcast traffic stays within a local area network(LAN) boundary; known as the broadcast domain. Layer 2 broadcast traffic is sent to the broadcast domain usinga MAC address of FF:FF:FF:FF:FF:FF. Every device in the broadcastdomain recognizes this MAC address and passes the broadcast trafficon to other devices in the broadcast domain, if applicable. Broadcastingcan be compared to unicasting (sending traffic to a single node) ormulticasting (delivering traffic to a group of nodes simultaneously).
Layer 3 broadcast traffic, however, is sent to all devices ina network using a broadcast network address. For example, if yournetwork address is 10.0.0.0, the broadcast network address is 10.255.255.255.In this case, only devices that belong to the 10.0.0.0 network receivethe Layer 3 broadcast traffic. Devices that do not belong to thisnetwork drop the traffic.
Broadcasting is used in the following situations:
Address Resolution Protocol (ARP) uses broadcasting tomap MAC addresses to IP addresses. ARP dynamically binds the IP address(the logical address) to the correct MAC address. Before IP unicastpackets can be sent, ARP discovers the MAC address used by the Ethernetinterface where the IP address is configured.
Dynamic Host Configuration Protocol (DHCP) uses broadcastingto dynamically assign IP addresses to hosts on a network segment orsubnet.
Routing protocols use broadcasting to advertise routes.
Excessive broadcast traffic can sometimes create a broadcaststorm. A broadcast storm occurs when messages are broadcast on a networkand each message prompts a receiving node to respond by broadcastingits own messages on the network. This, in turn, prompts further responsesthat create a snowball effect. The LAN is suddenly flooded with packets,creating unnecessary traffic that leads to poor network performanceor even a complete loss of network service.