I have a "Wireless Extended Network" using two of the latest 802.11ac Airport Extremes. This works very well with one bothersome and perplexing exception. Wireless clients can't seem to talk to other wireless clients unless they are on the same access point.
The practical problem with this is the wireless printer in the extended zone can't be seen (no ping, no web interface, and certainly no printing) from clients connected to the primary access point, even though clients in the extended zone have good internet connectivity, which obviously must go through the primary access point (which also acts as router and dhcp server).
The printer is a Xerox multi function with a rather odd little wireless bridge, pretty sure it's using some flavor of 2.4GHz to connect. The problem may lie with that somehow but given an IP connection works on one segment I'm not sure how I can blame it...especially given the oddness I see in AirPort Utility.
When connected to to the Extended access point The Airport Utility show the network properly and all with the little green "ok" symbol:
PrimaryAP ..... ExtendedAP ----- TimeCapsule
When connected to the PrimaryAP Airport Utility shows the ExtendedAP as "missing" but shows the TimeCapsule (which is connected to it by an ethernet cable) as OK
Solutions, leads, or even wild theories appreciated...