VLAN Size and Network Design

[alex.f.]

Hi,

what is the benefit of building a Network just for IP Phones (voice/video) with on big /22 VLAN on one Core (Catalyst 68xx VSS) with 15-20 FEX?

(The Network serves only voice traffic)

[Reza Sharifi · Accepted solution]

Hi,

It is usually better to keep the broadcast domain smaller. So, instead of a /22, you can create 4 /24s. This way if something happened to one vlan, it doesn't effect the other ones. Or if you want to apply a policy to one vlan and not all the other 3. Overall, segmentation gives you more flexibility.  

HTH

[Joseph W. Doherty]

FEX or specific, I believe, to Nexus series. Did you mean IAs?

On L3 switches, routing isn't the bottleneck it once was. Something like a Catalyst 68xx generally has sufficient resources to handle lots of networks. So, big networks, like your /22 don't really offer much in the way of any benefit. They can, though, tie up a large address block, which might have a low host usage. Also, a larger network (again like a /22) exposes host to the broadcast scalability issue. Lastly, if your ports are data/voice, your VoIP devices are exposed to physical port traffic, such as broadcasts, from the data VLAN too (although the VoIP phone "logically" will ignore it).