Collision and Broadcast Domains

Darian929

So here I am studying for my CCENT full time, to go onto CCNA later. Im watching the CBT Nuggets video which are great and I saw this video on how switching works and it talks about Collision and Broadcast DOmains and this is where I am sort of tipsy on. So I want to see if Im on the right track. A collision domain on a switch is seperated by each connection from one pc to a switch port... so in a switch there are different number of collision domains depending on how many PC's are connected to that switch? Am i correct or im understand it wrong? While on a hub there's only one, because since a hub doesn't work with MAC addresses, it will retransmit the packets to every port, forcing the PC's to listen and send one at a time.

Now for broadcast domains, this is depending on how many switches/hubs you have on your network correct? So if I have 2 switches connected to one router, and 10 pc's on each switch, I would have 2 broadcast domains...? Help me if I am complicating myself.

marioc

You are absolutely correct. Each port on a switch creates a collision domain. Each physical switch creates one broadcast domain. In a layer 3 switch multiple broadcast domains can be created by creating VLANs.

logicmyfoot

Think of a collision domain like. How many PC can transmit data together.
In a switch every PC connected can transmit simultaneously as switches work on FULL DUPLEX however a Hub operates in HALF DUPLEX hence only 1 PC can transmit or receive at any given time , so only 1 collision domain exists.

alan2308

marioc wrote: »

Each physical switch creates one broadcast domain.

Not necessarily. The simplest example of this is take two switches and connect them together, leave all ports on both switches in vlan 1. In this example, both switches are in the same broadcast domain.

Then take one switch, and add multiple vlans to it. Now you have multiple broadcast domains on one switch.

Monkerz

Darian929 wrote: »

Now for broadcast domains, this is depending on how many switches/hubs you have on your network correct? So if I have 2 switches connected to one router, and 10 pc's on each switch, I would have 2 broadcast domains...? Help me if I am complicating myself.

Broadcast domains are not figured by switches or hubs on your network. Heck, you can have one 48 port switch, divided into 48 vlans, one per port, equaling 48 broadcast domans, but vlans are accessed by routers. Without a router, 2 vlans couldn't communicate.

You need to remember that a router will not forward broadcast packets, thus a router divides broadcast domains. Each physical port on a router is a separate broadcast domain, and each vlan setup on the router is a separate broadcast domain.

A router is pretty much the Grand Central Station of networking.

Darian929

Yea im getting the hang of it and understand the VLAN concept because each VLAN does seperate broadcast domains. now I know this is good fundamental knowledge but is this really needed for ICND 1?

alan2308

Darian929 wrote: »

Yea im getting the hang of it and understand the VLAN concept because each VLAN does seperate broadcast domains. now I know this is good fundamental knowledge but is this really needed for ICND 1?

Here is the ICND1 blueprint. Requires free registration to access.

• Explain the technology and media access control method for Ethernet technologies

• Explain network segmentation and basic traffic management concepts
• Explain the operation of Cisco switches and basic switching concepts