Mike Albano writes on his dumping ground :
Long story short: Bonjour service advertisements, including those sent from Apple TV’s, have a destination address of link-local multicast 18.104.22.168. What this means is that the advertisements,by spec, will not cross a subnet boundary.
Who cares if at home & kind of a nightmare in the Enterprise.
Read more at: Using mDNS Snooping for ‘Bonjour’ support