One of the requirements of Apple's Bonjour service is that devices are in the same broadcast domain so that they can be discovered. They can be on different APs (and even different SSIDs) as long as the network behind them is the same.
Are you sure you want to do this? To pull it off you have to enable Bonjour multicast. You have to enable multicast and then define the Bonjour protocol as one that you allow. You should think about this carefully and lock this down to only the devices that you want to be able to do this. Hopefully they are devices that you own and so you can map them to a topology and only turn on this protocol for a select few. I think there are gateway solutions that help devices to find each other even when on separate VLANS. At my last institution we decided not to support Bonjour. I think it was an excellent choice. I think it could bring your network to its knees.
it is like Drew said: As long as the devices are on the same network they are able to discover - "see" - each other. The transport behind is regular multicast.
However, owning an Apple TV myself, I know this issue. My advice would be to disable the automatic shutdown of the Apple TVs and enable Bluetooth on the devices that shall use the Apple TVs. Doing both will at least give you reliable discovery and connections for the Apple TV in the same (maybe even neighbouring) room.
@John: As long as you have at least one device, e.g. a switch, that manages all the multicast traffic, Bonjour should not be that problematic. As far as I understand it, the discovery uses multicast - then called Bonjour -, while streaming uses unicast. This way, the bulk of the traffic is directed to a single host instead of being flooded all over the network.
(I have never verified this though.)
For my deployment with a bridge@EWC topology I've enabled
-Multicast bridging enabled
-Wireless replication enabled
You'd find it in > VNS > Topology > "your_topology" > Multicast Filters
Here a diagram from my test which isn't a real life scenario as you don't want to stream the traffic via the VPN link but I like complicated test setups :-)
dns-sd -B _airplayin Terminal which will show the underlying Bonjour services. If they disappear and reappear often then there definitely is a problem.
John, Bonjour can be managed successfully, but there are things you can do to make it better. We have lots of Apple TVs, wired to a VLAN that is also bridged@AP to our Staff topology. I have IPv6 blocked (which halves the multicast traffic) and the Apple TVs have static IPs assigned through DHCP (which avoids problems with Bonjour Sleep Proxy), and are set to never sleep. I also drop port 5353 from Apple TV MAC addresses with a policy on our core S4 so devices in each building on see nearby Apple TVs.
The issue with Apple TV's sometimes dropping out still happens but I feel it is not a network or setup issue. We can easily solve the random issue by just rebooting the APPLE TV. I believe that the Apple TV was never designed as an enterprise device to be placed on large networks SO that is why we have the few quirks that Apple TV's have. Mostly we find them ok.