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Private IP Subnetting, VLANs & Routing

With a VoIP rollout we would like to re-address our entire WAN network. I had some questions regarding how subnetting would work at the various WAN locations.

First off lets say every WAN site is given a /18 range, and various /23 ranges under that are reserved for specific network devices like VoIP Phones, Workstations, Servers, Perimeter Devices, etc.

I envision a network like this: (WAN Location 1) (Perimeter Devices) (Servers) (Workstations) (VoIP Phones) (WAN Location 2) (Perimeter Devices) (Servers) (Workstations) (VoIP Phones)

If we're using Layer 3 switches how do these subnetworks comunicate? Does each one have to have it's own VLAN?

I read an artical at:,289142,sid7_gci803121,00.html

Which states: "Avoid creating VLANs "for the sake of it." Be clear on the benefits that will accrue as a result of implementing VLANs when deciding how many VLANs to create. This decision cannot be made independently of the IP addressing plan, where the number of LAN subnets will usually correlate to the number of VLANs deployed."

Is mandating that specific ranges like this be used ok? If a WAN site has a router with a single Ethernet interface you can only really give it a single internal IP address and subnetmask. (Unless a bunch of "ip addresss n.n.n.n m.m.m.m secondary" commands would work)

So I'm guessing that's where the Layer 3 switch would come in?? We need seperate VLANS for the phones and Workstations regardless.

I want our IP addressing plan to work out, but I don't quite know enough about networking to be confident in the direction I'm going.


New Member

Re: Private IP Subnetting, VLANs & Routing

If anyone read throught this message, you comments would be appreciated! I'm trying to figure out the best way to match up a VLAN layout with an IP Address scheme...

Since interconnecting VLANS requires routing (or layer 4 switching?) this would raise equipment standards at various locations.

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