Broadcast Domain\Collision Domain

ztahie

hello !
I'm still confused between those 2.
1.can some1 please explain it to me ?
2.please give example with other devices (hub/switch/router) and how they can reduce\increase them in the network.

bmauro

Wooo Hooo. I know the answer to this one

A Broadcast domain is any segment that can recieve a broadcast (no duh). A good example would be if PC1 is trying to find the MAC address of another computer on it's LAN it will send a Broadcast frame to all devices on its segment asking for this information. The only way to stop broadcasts from propegating is to segment your network with Routers or by using VLANs.

A collision domain is any segment where two frames can have a collision. On an Ethernet segment, if two devices transmit a frame at the same time, the frames will collide and each device will have to re-transmit the frame following CSMA/CD algorithm. If you have more than one device on a segment, collisions can occur. Hooking PCs up to a Hub for instance is one collision domain since each PC is on the same ethernet (remember its like a bus). Bridges and Switches can be used to seperate collision domains. Bridges segment the network into two collision domains, while each port on a switch is its own collision domain. If you have a 12-port switch, each device in each port is in it's own collision domain and won't have any collisions with frames sent from the devices in the other ports. While bridges and switches increase the number of collision domains (which is good) they DO NOT stop or reduce Broadcasts, only Routers and VLANs do this.

That's my long winded answer, and please feel free to let me know if anything is incorrect.

ciscos

firtly about collision domain.They have to do with MAC (layer 2) filtering.

1 hub with 5 pc's attatched is one big CD and that is why one packet form one pc is not going to filtered and it will travel even to unwanted paths.
If you connect one hub to the above hub with 5 other pc's on it again you will have one VERY BIG CD for the same reason.NO mac filtering.

However...one switch with 5 pc's attathed is 5 CD.Because the lovely catalyst is going to build a table and it knows where to send one packet you have 5 CDs.
We can say now that is the first example after the connection of the second hub with the first one the CD has expanded and with the switch has been reduced.

Be careful that even if the number of CD is bigger (5 to 1)with the switch and that is because:
expanding a CD=less collision domains
reducing a CD=more collsions domains

if ok press any key to continue for the BD:)))))

Humper

bmauro wrote:

Wooo Hooo. I know the answer to this one

A Broadcast domain is any segment that can recieve a broadcast (no duh). A good example would be if PC1 is trying to find the MAC address of another computer on it's LAN it will send a Broadcast frame to all devices on its segment asking for this information. The only way to stop broadcasts from propegating is to segment your network with Routers or by using VLANs.

A collision domain is any segment where two frames can have a collision. On an Ethernet segment, if two devices transmit a frame at the same time, the frames will collide and each device will have to re-transmit the frame following CSMA/CD algorithm. If you have more than one device on a segment, collisions can occur. Hooking PCs up to a Hub for instance is one collision domain since each PC is on the same ethernet (remember its like a bus). Bridges and Switches can be used to seperate collision domains. Bridges segment the network into two collision domains, while each port on a switch is its own collision domain. If you have a 12-port switch, each device in each port is in it's own collision domain and won't have any collisions with frames sent from the devices in the other ports. While bridges and switches increase the number of collision domains (which is good) they DO NOT stop or reduce Broadcasts, only Routers and VLANs do this.

That's my long winded answer, and please feel free to let me know if anything is incorrect.

Thats a good explanation

Webmaster

Here's an overview with pics:
www.techexams.net/technotes/networkplus/networkcomponents.shtml

theseman

Collision Domain : Any easy way to remember this is: Hubs extend collision domains (If you have 10 workstations connected to a hub you have 1 big collision domain). Switches make multiple smaller collision domains. (In theory if you have 10 workstations connected to a switch you have 10 collision domains). Bridges also will create multiple (one for each port) collision domains.

In both of the above scenarios, you only have ONE Broadcast Domain. Broadcast operate at Layer 3 of the OSI model, and a Router is used to separate broadcast domains. This is called Segmentation. (Generally Routers do not forward broadcasts).

ztahie

o.k
u help me a lot
thanks

dublin_101

- each port of a switch is its own collision domain!

- a hub is one big collision domain (no matter how many pcs attached)

- each router port is its own broadcast domain!

- a serial wan connection from router to router is 1 broadcast domain, and 2. it is technically a collision domain also....

the explanation above was perfect!!!........

so you have one router connected to a 12 port switch with 12 pcs.........you'd have:

- 12 collision domains to the pcs
- 1 collision domain from the router to switch
- 1 broadcast domain from the router interface port to switch!

therefore, there'd be 13 collision domains and 1 broadcast domains!

dmaftei

dublin_101 wrote:

- each port of a switch is its own broadcast domain!

You mean collision domain; all ports are in one broadcast domain, unless you configure VLANs on the switch.

- a serial wan connection from router to router is 1 broadcast domain, and 2. it is technically a collision domain also....

There are no collisions on serial links, so technically you cannot talk about a collision domain in this case.

dublin_101

dmaftei wrote:

dublin_101 wrote:

- each port of a switch is its own broadcast domain!

You mean collision domain; all ports are in one broadcast domain, unless you configure VLANs on the switch.

- a serial wan connection from router to router is 1 broadcast domain, and 2. it is technically a collision domain also....

There are no collisions on serial links, so technically you cannot talk about a collision domain in this case.

sorry, i corrected it.........

yes i know that serial wan connections are broadcast domains, but recently when doing a quiz, my instructor said always keep in mind that technically it is a collision domain also...hence me using the word "technically"...

EdTheLad

dublin_101 wrote:

yes i know that serial wan connections are broadcast domains, but recently when doing a quiz, my instructor said always keep in mind that technically it is a collision domain also...hence me using the word "technically"...

A collision domain is a single CSMA/CD network which may consist of two or more Medium-Access Control (MAC) sublayers.

A collision domain is a logical area in a computer network where data packets can "collide" with one another.

These are just a couple of technical descriptions of a collision domain.So technically your instructor is incorrect.Ask him how its possible to have a collision on a ptp link?where the end systems dont even have addresses.

dmaftei

dublin_101 wrote:

yes i know that serial wan connections are broadcast domains, but recently when doing a quiz, my instructor said always keep in mind that technically it is a collision domain also...

Well then maybe you should tell your instructor that it's a nonsense to call a "collision domain" a medium in which it's impossible to have collisions...

darkuser

I experienced a collision once ..... and on a half-duplex connection !!!!