Collision Domain vs Broadcast Domain

I am going to write on the difference between the Collision and Broadcast domain. Most of you already knew about it but it will be very helpful for the starters of the networkers.

It is one of the basic article to start with in the networking field. One should always remember the difference between Collision and Broadcast domain. 

Broadcast Domain

Broadcast domain is a layer 2 domain where one broadcast and the message will be sent to everybody in a domain. So if we talk about broadcast domain. every LAN network has 1 broadcast domain which is connected to the router. So if you connect 5 different LAN networks with 5 ports on the router it means that there are 5 broadcast domains. 

So for every broadcast domain you can have multiple switches but have single router with a port. Let me explain you with the example. Can you let me know how many broadcast domains are there ?

Let me tell you that there is two Hubs connected to the users and one router in between. There is no Switch at all.

Fig 1.1- Sample Network

well as i already discussed every port of the router defines 1 broadcast domain so in the above example there are two different LAN networks connected to 2 different port of the router. so you can say that there are 2 Broadcast domain in the above shown diagram.

Collision Domain

Let's talk about Collision domain now, when two different devices send a packet at the same time on the shared network like Ethernet there might be collision and the domain is called as Collision domain. So every port of the switch have 1 collision domain. Let me take the same example. Tell me how many collision domain are there in the above shown Fig 1.1.

Well you are right there are 2 collision domain as well, So here in this case router will break the collision domain as well.

Note : Router breaks Collision as well as Broadcast domain while switch breaks the Collision domain.

Hope it will clear your concept on Broadcast and Collision domain. Now take an another example and let me know how you think about the below shown example with how many collision and Broadcast domains are there ?

Fig 1.2- Sample Topology 

So i guess you guys understand, the answer is 1 broadcast domain and 6 collision domain. Hope you understand now with this Fig 1.2 as there is no router and 2 switches which is connected to 3 -3 different hubs. As i mentioned Switch breaks the Collision domain, so it breaks 6 collision domain in the above shown Fig 1.2 example and this network will have 1 broadcast domain, it will break only when we are going to connect the router in the network else connecting more switches or hubs will have same 1 broadcast domain.