This is when it becomes useful to configure VLANs. Also, it may be preferable to separate certain clients into different broadcast domains for security and policy reasons. Large layer 2 broadcast domains can be susceptible to certain unintended problems, such as broadcast storms, which have the ability to cause network outages. Broadcasts are contained in the same layer 2 segment, as they do not traverse past a layer 3 boundary. Any broadcast traffic on a switch will be forwarded out all ports with the exception of the port the broadcast packet arrived on. Within a layer 2 switch environment exists a broadcast domain. It then sends the packet to the appropriate destination MAC address which the switch will then forward out the correct port based on its MAC-Address-Table. It does not know the unique MAC address however, until it discovers it through an ARP, which is broadcasted throughout the layer 2 segment: Here, PC A wants to send traffic to PC B at IP address 192.168.1.6. What is needed however is the destination MAC address which can be resolved through the Address Resolution Protocol (ARP) as illustrated below: Devices in the same layer 2 segment do not need routing to reach local peers. Routing operates at layer 3, where packets are sent to a specific next-hop IP address, based on destination IP address. Traditional switching operates at layer 2 of the OSI model, where packets are sent to a specific switch port based on destination MAC addresses.
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