Voice VLAN Recommendations

jusan101781 · ‎03-03-2016

We have a dedicated VLAN for voice and currently have a /24 subnet mask DHCP pool tied to it which allows for 253 addresses in our current setup. However, we are expecting 1500 clients on this voice vlan so we want to expand the pool to a /21 to allocate for all these devices. What is the recommended max for voice vlan /24, /23, /22? Would this cause any type of issues (broadcast, arp, etc.)? What is the recommended setup? Tie multiple pools, networks to the VLAN instead of expanding it?

I looked around on Cisco documentation and could not locate any best practices or recommendations regarding this. Any recommendations? Below is our current setup:
----------

Headquarters:
Anticipate 1500 phones at our headquarters.
We have three buildings with multiple floors at HQ. Currently, each floor shares the same voice vlan (VLAN 500), SVI is at the core.

Remote Offices:
Connected through MPLS. Each have their own dedicated voice vlan /24 (VLAN 500 at each site), more than sufficient for their respective office.

*****
Core:
sh run int vlan500
Building configuration...

!
interface Vlan500
description VOIP
ip address 10.199.180.1 255.255.255.0
no ip redirects
no ip unreachables
no ip proxy-arp
end

sh run | s VOIP
ip dhcp pool VOIP
network 10.199.180.0 255.255.255.0
default-router 10.199.180.1
option 150 ip 1.1.1.1 2.2.2.2
dns-server 8.8.8.8 8.8.4.4
lease 0 8
*****
Sample port config from floor switch:
interface GigabitEthernet5/27
switchport access vlan 100
switchport mode access
switchport voice vlan 500
auto qos voip cisco-phone
qos trust device cisco-phone
spanning-tree portfast
service-policy input AutoQos-4.0-Cisco-Phone-Input-Policy
service-policy output AutoQos-4.0-Output-Policy
end

Reza Sharifi · ‎03-03-2016

There is no official documentation but usually I use a /24 for voice and a /24 for data per floor.

If you have 3 building with multiple floors and 1500 phones and 1500 users. lets say each building has 3 floors. So you can do

bulding-1 floor-1

192.168.10.0/24 vlan 100 for data and 192.168.11.0/24 vlan 110 for voice

bulding-1 floor-2

192.168.20.0/24 vlan 200 for data and 192.168.21.0/24 vlan 210 for voice

bulding-1 floor-3

192.168.30.0/24 vlan 300 for data and 192.168.31.0/24 vlan 310 for voice

and so on...

HTH

Joseph W. Doherty · ‎03-03-2016

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

I recall coming across another (major) VoIP phone vendor that recommended up to /24 for data and voice, when both share the same port, or a /23 for just voice, when ports not shared.