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TOPIC: Broadcast Domain - Partitioning

Broadcast Domain - Partitioning 15 years 5 months ago #2537

hey again :-)

I know that switches partition collision domains and routers partition both collision and broadcast domains, but when we subnet we are partitioning our address into smaller collision domains AND broadcast domains?

Also with switches and other intelligent hardware being so cheap these days, is subnetting going to die out? or what benefits do we have when we use routers on the network etc ?
Love your Optical Drive :-)

Re: Broadcast Domain - Partitioning 15 years 5 months ago #2539

  • tfs
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I assume the first paragraph was a question and the answer is yes. When you subnet, you subnet with a router, as you need a router to go from one subnet to another. Each subnet is it's own broadcast domain.

The fact that switches are getting cheaper, as are other components, does not negate the need for subnets. You use subnets to separate logical entities, such as accounting from marketing. As your number of hosts increase, there is going to be more and more traffic on your network and subnetting decreases the traffic. Now, with layer 3 switches, you have VLANS that can do the work of separating the broadcast and collision domains and they are doing a routing function. But you still need to route between subnets using either a router or special software components to a Layer 3 switch to allow it to route.


Re: Broadcast Domain - Partitioning 15 years 5 months ago #2548

The biggest reason for subnetting was to divide broadcast domains so you don't millions of machines broadcasting on one segment. Pure layer-2 switching still handles broadcasts by flooding to all ports, so the traffic does not get lessened. If you add VLANs into the mix then they do segment the broadcast domain, but as tfs said, you have to route between VLANs so you either shove in a router or get a layer-3 switch.

Remember that routing is in layer 3 (network layer) of the OSI model, whereas switching is done at layer 2 (data-link layer). Thus neither can replace the other.

Its like asking whether we can all stop using IP addresses and replace them with ethernet addresses.

Lol, I've started to confuse myself these days.
Sahir Hidayatullah. Staff - Associate Editor & Security Advisor

Re: Broadcast Domain - Partitioning 15 years 5 months ago #2552

Ok thanks both, that has answered my question nicely :-)

If you have the time could ya give my question on subnetting a bash, just wanna clear that up in my mind :)

Love your Optical Drive :-)

Re: Broadcast Domain - Partitioning 15 years 5 months ago #2553

evening all :]
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