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Please can any one tel me that how many colision domain and broadcast domain will be there in router, switch , hub and bridge.

Please can any one tell me that how many collision domain and broadcast domain will be there in router, switch , hub and bridge.

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Cisco Employee

 Hello, To further your

 

Hello,

 

To further your understanding of broadcast domains on switches you should understand the concepts of Vlans. Vlans can be used to create additional broadcast domains on a switch. By default a switch will have 1 broadcast domain called Vlan01. Any additional Vlans that get created will increase the number of broadcast domains. For example adding Vlan10, and Vlan30 would create a total of 3 broadcast domains. Hope that clarifies how to determine how many broadcast domains are on a switch. 

 

-Justin  

 

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Silver

Hi Nitin,This can be

Hi Nitin,

This can be explained as below:

Collision domain:
It can be defined as a set of LAN devices whose frames could collide with one another.  

Broadcast Domain:
Broadcast domain can also be seen as a collision domain. It can be defined as a set of devices such that when one device sends a broadcast frame all other devices will receive that frame in the same broadcast domain.

1.) HUB: 

  • HUB works on L1 of OSI.
  • Only one data packet can pass through the hub at a time.
  • A lot of collisions are present, because of only 1 collision domain.


2.) Switch

  • It supports simultaneous connections
  • It sends traffic to the destination port. This is done because of a feature known as ARP (Address resolution protocol). The main job carried by this protocol is that it converts IP to MAC address.
  • Due to this a table is mentained in which every device is mapped using IP and Mac address.
  • Multiple Collison Domain, i,e A single collison domain is attached with every single port. For eg If you have a switch of 24 ports then you have 24 Collison domains.


3.) Routers:

  • Works on L3 of OSI
  • Routers doesnt propagate broadcast traffic, two different subnets/LAN/Networks communicates through router via routing protocols
  • Routers can take and forward "unicast" traffic
  • Each interface present on router gives rise to broadcast domain

 

Regards,

Anim Saxena

Community Manager : Security

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Cisco Employee

It's easy. Think about it as

It's easy. Think about it as follows.

Hub and bridge operate at L1 of the OSI (physical layer) hence they don;t have info about the destination or source (MAC or IP) and so any packet sent through this media will always get broadcast to all port to hit the right destination and so all other ports shall not send at the same time or a collision will occur..

So Bridges and Hubs = 1 broadcast domain and 1 collision domain.


Access switches or L2 switches operate at L2 (data link layer), source MAC and destination MAC. It also has a table that maps port to MAC address and vlan info. to know what devices are connected to which ports. and which Vlans. so the Switch is more intelligent that it has this info. so it can actually switch the packet to the required destination. so this means that every port has it's own collision domain.

The switch forms this table by listening to ARP messages. If the switch receives a packet for a destination MAC that it didn't learn about, it broadcasts to all ports within the same VLAN, hence it can be considered 1 broadcast domain per Vlan.

So switch = 1 BC domain per each VLAN and 1 collision domain / port.

 

Routers operate at L3 (network layer) so they have info. about IP and MAC addresses. It has an ARP table that contains info. about the IPs, MACs and ports. Hence it can route towards the right direction through the IP info and towards the right port through the MAC. It's like the switch except it has more info. (src and dest IP addresses) So it knows the bigger picture of how to reach the destination.

So routers = 1 BC domain and 1 collision domain / port.

Cisco Employee

 Hello, To further your

 

Hello,

 

To further your understanding of broadcast domains on switches you should understand the concepts of Vlans. Vlans can be used to create additional broadcast domains on a switch. By default a switch will have 1 broadcast domain called Vlan01. Any additional Vlans that get created will increase the number of broadcast domains. For example adding Vlan10, and Vlan30 would create a total of 3 broadcast domains. Hope that clarifies how to determine how many broadcast domains are on a switch. 

 

-Justin  

 

Community Member

Thanks for just a wonderfull

Thanks for just a wonderfull clarificaiton justin..

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