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New Member

how to count Collision doamins and broadcats domains in network

I understand the difference between Collision Domains & Broadcast Domains, my problem is that I can't figure out how to count them in a network. Would someone please post a diagram and illustrate in details the best way to count them!!!

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Accepted Solutions

Re: how to count Collision doamins and broadcats domains in netw

All ports of a hub are in the same collision domain and broadcast domain. Whether the domains expand beyond a connected device depends on the type of device, and in some cases, the configuration of the device.

Two hubs connected to separate interfaces of a router would result in two collision domains, and two broadcast domains.

Routers separate broadcast domains. In the context of this discussion, when you are talking broadcast domains, you are talking about Layer 2 communication (MAC).

The only devices that will receive and process the MAC broadcast are the hosts connected to that hub, and the network interface of the router connected to that hub.

6 REPLIES
Cisco Employee

Re: how to count Collision doamins and broadcats domains in netw

Hmm.. Every Vlan is a broadcast domain and each switch port is a collision domain on switch.

Count the number of vlans that you have in your network, that will be the number of broadcast domains. If you are using VTP in your network, it will be easier to count the number of vlans.

Each port is a collision domain so count the total ports that you have in your network.

-amit singh

New Member

Re: how to count Collision doamins and broadcats domains in netw

Hi thanks for reply

i have this diagram

hib is connected to 5 pcs and hub is connected to router.ther eis other switch which has 5 pcs connected nthis switch is also connected to router.

now how many CD and Bd will be there?

thanks

Re: how to count Collision doamins and broadcats domains in netw

Your typographical errors make it tough to determine whether there are one or two switches (ref.: other switch).

Assuming there is only one switch and one hub, and they are each connected to separate router interfaces, with no connections between the hub and switch:

All of the PCs connected to the hub are in the same collision domain, and same broadcast domain (incl. the hub to router connection).

The switch has one router connection and five host connections for a total of six connections. This represents six additional collision domains. All of these six connections are a common broadcast domain (assuming no VLANs).

You have 2 broadcast domains (one on each side of the router), and seven collision domains (one for the hub, and six on the switch).

New Member

Re: how to count Collision doamins and broadcats domains in netw

Hi michael ,

thanks for eply you are right u have correct

answer.

there is no connection between hub and other

switch.

So connection to HUB is always considered as

1 CD?

if we have 2 hubs connected to Router on 2 different interfaces then we would have 2

CD right and still 1 BD?????????

Re: how to count Collision doamins and broadcats domains in netw

All ports of a hub are in the same collision domain and broadcast domain. Whether the domains expand beyond a connected device depends on the type of device, and in some cases, the configuration of the device.

Two hubs connected to separate interfaces of a router would result in two collision domains, and two broadcast domains.

Routers separate broadcast domains. In the context of this discussion, when you are talking broadcast domains, you are talking about Layer 2 communication (MAC).

The only devices that will receive and process the MAC broadcast are the hosts connected to that hub, and the network interface of the router connected to that hub.

New Member

Re: how to count Collision doamins and broadcats domains in netw

Thanks for helping

Great reply

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