Collision Domain and Broadcast Domain + Examples

In Ethernet LAN's computer must first listen to the media and make sure the media is idle, then they can transmit their data. After a transmission has been sent, the computers on the network compete for the next available idle time to send another frame.

When two stations listen for network traffic to ensure media is idle and they hear nothing, they transmit simultaneously. So, collision is happened, that is why CSMA/CD is used in Ethernet LAN's. This happens in devices use half-duplex like hubs. Because all the devices on a Layer 1 Ethernet segment share the bandwidth, only one device can transmit at a time. But switches eliminate this problem by separating collision domains.

Collision Domain:

  • A collision domain is, as the name implies a part of a network where packet collision can occur.
  • A collision occur when two devices send a packet at same time on the shared network segment.
  • The packets collide and both devices must send the packets again which reduces network efficiency.
  • Collision are often in a hub environment, because each port on a hub is in the same collision domain.
  • By contrast, each port on a bridge, a switch or a router is in a separate collision domain.
what is Collision Domains example
Collision Domain Example
As you can see we have 6 collision domains occurs.

Tip: remember each port on a hub is in the same collision domain. Each port on a bridge, a switch or router is in a separate collision domain.

Broadcast Domain:

  • A broadcast domain is a domain in which a broadcast is forwarded..
  • A broadcast contains all the devices that can reach each other at data link layer of OSI model(layer2) by using broadcast.
  • All ports on a hub or a switch are by default in the same broadcast domain.
  • All ports on a router are in the different broadcast domains and routers don't forward broadcast from one broadcast domain to another.
what is broadcast domain example
Broadcast Domain Example
 In the above picture we have three broadcast domains, since all ports on a hub or a switch are in the same broadcast domains, and all ports on a router are in a different broadcast domain.

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