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Home > Archive > CCNA > January 2001 > broadcast and collision domains
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broadcast and collision domains
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| broadcast and collision domains are a bit confusing to me between switches, bridges, routers, and hubs. Can someone give a breif description so other things that I am trying to learn comes easier to me. Thanks | |
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| switch: one collision domain per port; one broadcast domain per VLAN.
bridge: one collision domain per port; one broadcast domain per bridge.
router: one collision domain per port; one broadcast domain per port.
hub: one collision domain per hub; one broadcast domain per hub.
Is this enough, or you need more details?
Cheers!
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| i'll try this... someone please correct me if i am wrong -- it's still a little new to me.
collision domain: all network traffic (normal traffic and broadcast/multicast traffic) competes for the same bandwidth. think of a hub. all the devices connected to a hub are in the same collision domain so they all compete for the bandwidth there. if 2 devices transmit at the same time, the packets collide and need to be resent. highly populated hubs make for a waste of your high-speed cabling. switches/bridges seperate your network into multiple collision domains. with a switch it's more like a 1:1 collision domain meaning that after the switch has built it's CAM table (database of MAC addresses), then the traffic destined for node A from node B only gets send to node A and not to the whole network.
broadcast domain: all devices on a hub are also in the same broadcast domain. all devices on a switch/bridge are in the same broadcast domain. keeping with the 2 nodes as listed above, if the switch doesn't know where node A is, then the switch wil broadcast the packet to all devices in this broadcast domain (all devices connected to the switch) to see where it's at. when it gets the response from node A, it adds the MAC to the CAM table so it knows next time and won't need to broadcast that packet any more.
routers seperate broadcast domains in effect by not forwarding broadcast messages.
i hope that helps. and if someone has something to add that can help the both of us, please do.
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chunder -- Network+, MCSE, CNE | |
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| quote:
Originally posted by chunder:
i'll try this... someone please correct me if i am wrong -- it's still a little new to me.
all devices on a switch/bridge are in the same broadcast domain. keeping with the 2 nodes as listed above, if the switch doesn't know where node A is, then the switch wil broadcast the packet to all devices in this broadcast domain (all devices connected to the switch) to see where it's at.
Sounds like you have the concept. The one thing I'd add: the above is true only when you only have one VLAN on your switch. If there is more than 1 VLAN, each VLAN is its own broadcast domain. (That's why VLAN's were invented.  )
HTH,
doctorcisco
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Silicon is made from sand; nothing made from sand is allowed to wreck my day! |
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