Hi Mark,

first of all, sorry for my English, I'm from France.

Collision Domains

- layer 1 of the OSI model

- a hub is an entire collision domain since it forwards every bit it receives from one interface on every other interfaces

- a bridge is a two interfaces device that creates 2 collision domains, since it forwards the traffic it receives from one interface only to the interface where the destination layer 2 device (based on his mac address) is connected to. A bridge is considered as an "intelligent hub" since it reads the destination mac address in order to forward the traffic only to the interface where it is connected

- a switch is a multi-interface hub, every interface on a switch is a collision domain. A 24 interfaces switch creates 24 collision domains (assuming every interface is connected to something, VLAN don't have any importance here since VLANs are a layer 2 concept, not layer 1 like collision domains)

Broadcast Domains

- layer 2 of the OSI model

- a switch creates an entire broadcast domain (provided that there's only one VLAN) since broadcasts are a layer 2 concept (mac address related)

- routers don't forward layer 2 broadcasts, hence they separate broadcast domains

With all this information, you can say that on your diagram, there are 2 broadcast domains (1 router that separates 2 LAN segments composed by one or many switches, with only 1 VLAN per segment).

There are 8 collision domains, one per pair of devices connected to each other (switch to router, switch to swich, switch to computer etc...) since we are talking about layer 1 concept (physical connection).

Hope that helps

Matthieu (from France)

Yep and a switch creates only one broadcast domain , unless there is more than one VLAN configured

Thanks Brother from frans side,

Praise the Lord.But dear my one Q is still not answered is

what is it mean exactly the word " colison domain" & "brodcast domain" ?? what happen exatcly with data or frame or packet?

COLLISION DOMAIN

A collision domain is a physical network segment where data packets can "collide" with one another for being sent on a shared medium, in particular in the Ethernet networking protocol. This is an Ethernetterm used to describe a network scenario wherein one particular device

sends a packet on a network segment, forcing every other device on that

same segment to pay attention to it.

A group of Ethernet or Fast Ethernet devices in a CSMA/CD LAN that are connected by repeaters and compete for access on the network. This situation is typically found in a hub environment where each host segment connects to a hub that represents only one collision domain and only one broadcast domain.

Only one device in the collision domain may transmit at any one time,

and the other devices in the domain listen to the network in order to

avoid data collisions. Collisions decrease network efficiency; if two

devices transmit simultaneously, a collision occurs, and both devices

must retransmit at a later time.

The basic strategy goes like this:

• A computer listens on the cable to see if another computer is
  transmitting, which is indicated by a voltage change on the cable. If
  busy, the computer waits and listens.

• When the cable is not busy, a computer attempts to transmit.

• Another computer may attempt to transmit at the same time, which causes a collision.

• Both computers that attempted to transmit must back off, wait a random period of time, and then attempt to transmit again.

Computers on the network detect collisions by looking for abnormally

changing voltages. Signals from multiple systems overlap and distort

one another. Overlapping signals will push the voltage above the

allowable limit. This is detected by attached computers, which reject

the corrupted frames (called runts).

BROADCAST DOMAIN

A broadcast domain is a logical division of a computer network, in which all nodes can reach each other by broadcast at the data link layer.

In terms of current popular technologies: Any computer connected to the same Ethernet repeater or switchis a member of the same broadcast domain. Further, any computer

connected to the same set of inter-connected switches/repeaters is a

member of the same broadcast domain. Routers and other higher-layer devices form boundaries between broadcast domains.

I hope above information helps..

There's a collision domain between each host and the respective switches, as well as between the switches themselves. So each individual link is a collision domain.

The broadcast domain would be defined by your vlan scope.

HTH,

Scott

In this diagram, there would be 9 collisions right?