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Designing vlan

What might be suitable vlan size i mean broadcast domain size. Howmany end users in one vlan. What is the basic risk of creting too big broadcast domains.

Thanks

Juha

2 REPLIES
Hall of Fame Super Blue

Re: Designing vlan

Hi Juha

Different people use different guidelines but a commonly accepted size is a class C network ie /24. A lot does depend on the applications you are running on the vlans ie. if they use a lot of broadcasts to function then you may need a smaller size.

We use /25's per vlan where i work which gives 126 useable IP addresses.

The basic risk of too big a broadcast domain is that your clients spend too much time and resources processing broadcast traffic that may or may not be for them.

HTH

Jon

Re: Designing vlan

Just to add a little more t Jn's comment, keeping the subnet size small also helps should you have problems along the lines of code red or SQL slammer. Once a subet is identified as having an infected device, shutting down the VLAN as the first step before locating the infected device has a lower impact on other users - you are less likely to get grief for taking 70 users offline than if you took 400 users out for a single infected device.

Going for smaller subnets also makes the use of L3 links between switches potentially more practical.

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