Broadcast Domains

In this article we will discuss Broadcast Domains, will make brief discussion on Broadcast Domains, In last article we discuss about Reasons for Subnetting.

In an Ethernet LAN, devices use broadcasts to locate:

  • Other devices – A device uses Address Resolution Protocol (ARP) which sends Layer 2 broadcasts to a known IPv4 address on the local network to discover the associated MAC address.
  • Services – A host typically acquires its IPv4 address configuration using the Dynamic Host Configuration Protocol (DHCP) which sends broadcasts on the local network to locate a DHCP server.

Switches propagate broadcasts out all interfaces except the interface on which it was received. For example, if a switch in the figure were to receive a broadcast, it would forward it to the other switches and other users connected in the network.

Routers do not propagate broadcasts. When a router receives a broadcast, it does not forward it out other interfaces. For instance, when R1 receives a broadcast on its Gigabit Ethernet 0/0 interface, it does not forward out another interface.

Therefore, each router interface connects a broadcast domain and broadcasts are only propagated within its specific broadcast domain.

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