-first you need to make a mDNS-profile; Cisco Provides a default with the most common services but that default might not include all the service-strings your mDNS-devices broadcasts. Either read the documentation on the mDNS-device and add any mentioned service-strings, or sniff the chromecast-VLAN for all mDNS-broadcasts and make a list of offered service-strings. The Standard Chromecast servicestring is "_googlecast._tcp.local." or "_chromecast._tcp.local." but it depending on vendor (my experience it's usually the "Smartboard"-vendors that does this) it might be "VendorArbitrarilyChosenUniqueIDForThisSpecificDevice._tcp.local" (this basically means you need to add exactly every devices specific string intead of just "_googlecast._tcp.local").