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What is the best design?

What is the recommended and maximum amounts of IP phones in a single vlan.

Is it best to split the IP phones into multiple vlans or is it best to have only 1 voice vlan.

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Re: What is the best design?

The answer depends more on your network topology than on any absolute numbers. If you are talking about a small remote site with a single switch connected to an edge router, a single voice VLAN is fine. If you are talking about a larger site or campus, best practice dictates separate voice VLANs for every edge switch, with layer 3 switching enabled. That will allow you to load balance over multiple layer 3 uplinks to your core, and will also result in faster failover if one the links drops.

If you cannot run layer 3 links to the edge you will run into Spanning Tree constraints, though using Cisco features like Uplinkfast (or 802.1W) will speed up failover. You would then need ar least 2 VLANs on each edge switch, if you wanted to be able to load balance your traffic over multiple layer 2 links. Those same 2 VLANs could be used on multiple edge switches.

I have never seen a number on max phones per VLAN, but since they are not broadcast intensive, the practical limit is probably pretty large. My personal, conservative approach has been to use 24 bit mask subnets, limiting the max to 253. The big risk in a large flat network would be someone screwing up a switch config, creating a loop, resulting in a broadcast storm that would knock down an entire subnet. Limiting the size would reduce this risk somewhat.

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