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Subnets and Broadcasts Storms

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12 replies

by rakesh.chawda

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Hi All

We are currently using 3com 3300/3900 switches, in a 5 floor building, all floors have a 3300 switch connected to the main 3900 switch on the first floor by fibre modules.
We want to subnet our network to reduce bradcast storms, and to know who is on what subnet.

I have been told to get a switch and set up Vlans or get a router in. I dont know which is best to speed up network access.

Also our current switch can create Vlans, but in each Vlan how does it know the IP address ofthe other Vlan (hope this makes sense.

But any info on Valns or reducing broadcasts will be helpful.

Cheers

rakesh

12 replies

by Former member

You will need a router or RSM in order to route between VLANs. So, create the VLANs on the switch, trunk the connection between the switch and router, and then you can route between VLANs, or at least to them. But the switch and router must be able to agree on the trunking protocol.

by Former member

A comment about the note below: Switches do not control broadcasts (nor should they), so the poster below is in error. Unless of course a L3 switch with routing enabled...Only subnetting and routing can control broadcasts..

by Former member

Also in regards to your question about books, the internet has a wealth of information concerning VLANs, trunking and routing, starting as Cisco.com.

If your interested in switching, purchase a study guide for the CCNP test ###-503 (or 504) I believe, it should be entitled "Switching".

by madcateast

A managed switch should let you disallow broadcasts from traveling to other networks/or ports. If the 3Coms do not allow this set each floor or dept to a different network ie: 192.168.1.0, 192.168.2.0, etc. and use a router in place of the 3900. Unless told to do so a router will not forward a broadcast. This may also mess up a Windows environment with name resolutions (DNS, WINS etc) so helper servers or hard coding the servers may need to be done.

by rakesh.chawda

Q

Thanks for the Tip, is there any books you and anyone else knows of that will illustrate in Subnetting a network using switches and routers

by yasirs

Hi,

Guessing from your question , you probably have hubs attached to the individual ports of the switch. But switches do control broadcasts , thats why frame tagging was invented the packet is tagged on entry to the switch and un tagged on the link port ( say to the lower network devices hubs, PCs etc) but not untagged to share VLAN info over the trunk to another switch. So if u implement VLANS u r controling the broadcasts in a hardware sort of way. But now for the different VLANS to intercommunicate u would require either a ISL (Inter switch link) supporting router or a RSM route switch module. Also as the servers and its requests and processes are usually most requested I would advise a ISL card for the server it greatly improves response time.
Now if u don't presently have a router and u need to get one then use it for subnets and U'D BETTER KNOW UR TCP/IP inside outside anyside , but this process will cause about a 10% extra delay to ur response time on the network. Oh yeah since ur using 3com then well be sure they are inter operable with cisco... I would advise cisco any day for network equipment , they have good equipment and even better tech support , and it doesn't matter how much the products price is they PHONEU THEMSELVES TO FIND HOW THE SITAUTION IS GOING!!!

Keep the above in consideration and do as you wish.

Configuring these shouldn't be too hard just look up the sybex CCNA 2.0 book 640-507 that should be good enough.

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