VLAN IP Addressing Question

When establishing VLANs using Cisco components (routers, switches, WAPs), is it best to assign each VLAN an entire network (i.e. VLAN1 = /24, VLAN2 = /24) or can a single network be subnetted to conserve addresses (example VLAN1 = /26, VLAN2 = /26, etc.) ?

I know the initial reaction to this might be "You have all kinds of private address space to work with so why is this an issue? Just assign a network to each VLAN." The issue is that my company uses a central address registrar for private addressing and is stingy on letting too many networks get assigned for fear someday everything will be used up (I seriously doubt that will ever happen.) I feel I need 15 VLAN's across three offices so I was hoping to ask for /20 which would yield 16 separate, continuous networks where I would then assign one network to each VLAN and still have a spare network. I do not have anywhere near 4096 hosts so yes, I am wasting addresses.

The question comes down to: Is a VLAN configuration even possible subnetting a single network, or should I push for separate networks for each VLAN for ease of configuration and keeping my sanity.

Thanks in advance for any ideas.

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YES geting seperate subnets for seprate vlans is best idea to work on.


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CK and are each "entire" networks.

Classful subnets are long gone.

My initial reaction was "why don't you give us enough information so that we can see what you're trying to accomplish, how you have considered going about doing that and what constraints you are operating under".

So one constraint you are operating under is that you can't use a whole /20 unless you can justify to your internal registrar that you need a whole /20.

And the subtext is that you can't justify it to your internal registrar because you do not, in fact, need a whole /20.

It is entirely possible to subnet a /22 allocation into sixteen separate /26 networks.

What is it that concerns you about such an arrangement?

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There's nothing special about VLANs that should impact how you assign addresses. As far as addressing is concerned, they're just like separate physical LANs.

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Barry Margolin

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