Broadcast message on a network

Broadcast message on a network
Server
172.16.1.0/24
Host C
Host A Host B
Host X
Server
172.16.1.0/24
Host C
Host X Host A Host B
Multicast Overview
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A good example of a broadcast message is an Address Resolution Protocol (ARP) request.
When a host has a packet, it knows the logical address of the destination. To get the packet to
the destination, the host needs to forward the packet to a default gateway if the destination
resides on a different IP network. If the destination is on the local network, the source will forward
the packet directly to the destination. Because the source doesn’t have the MAC address
it needs to forward the frame to, it sends out a broadcast, something that every device in the
local broadcast domain will listen to. This broadcast says, in essence, “If you are the owner of
IP address 192.168.2.3, please forward your MAC address to the source address of this frame.”
Each device will answer a request for its own IP address, but a correctly configured router can
serve as a proxy as well, with the process of Proxy ARP.
This brings up another good point: Broadcasts can cause problems on networks. Because the
broadcast frame is addressed to include every host, every host must process the frame. CPU
interruption occurs so that the frame can be processed. This interruption affects other applications
that are running on the host. When unicast frames are seen by a router, a quick check is
made to identify whether the frame is intended for the host. If it isn’t, the frame is discarded.