Hello!
By default, multicast and broadcast traffic is suppressed by WLC and there is no "broadcast domain" so you can use networks bigger then /24.
"The wireless VLAN should be no larger than a Class B network or /16 and no smaller than a Class C network or /24. Cisco's San Francisco office is estimated at 3,300 IPs, and requires at least a /20 subnet with 4094 IPs for it's wireless VLANs."
https://documentation.meraki.com/MR/Deployment_Guides/High_Density_Wi-Fi_Deployment_Guide_(CVD)
"The WLC CAPWAP split MAC method treats broadcast traffic differently, as shown in Figure 2-35. In this case, when a broadcast packet is sent by a client, the AP/WLC does not forward it back out the WLAN, and only a subset of all possible broadcast messages are forwarded out a given WLAN's wired interface at the WLC."
http://www.cisco.com/c/en/us/td/docs/wireless/controller/8-1/Enterprise-Mobility-8-1-Design-Guide/Enterprise_Mobility_8-1_Deployment_Guide.html
Alexey
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