Can't see Airplay targets ICX 7150

[BlueSystems99]

Hi there

I am having trouble with Airplay on an ICX / Unleashed network.  I have seen this on a new site deployment and now on a sandbox environment in the office.

Topology is a 3rd party router (Draytek) set up as DHCP server for all VLANs.

ICX 7150-48P is only switch in sandbox, running Router mode on 09.0.10j_cd5.

I have a single Unleashed AP on management VLAN 1.  It is on a 'trunk' port of the ICX, with VLAN 1 untagged and VLAN 20, 30 tagged.

It is broadcasting 2 x SSIDs, one on WLAN 20 and one on WLAN 30.

ICX is set up for Multicast with IGMPv3 snooping & querying.  

I have Airplay targets on VLAN 20, but I cannot see them from my iPhone, which is also on Wifi WLAN 20 / VLAN 20.

Everything else on the network seems to be working fine.  I have had this working fine on a previous L2+ switch so I *think* it's an issue/setting on the ICX.

I have tried enabling Bonjour Gateway on the AP but that seems to be managing cross-VLANs, which I'm not trying to do.  All my Airplay traffic should stay on VLAN 20.

Any ideas?

[BlueSystems99]

addendum:

If I disable Multicast globally [(config)# no ip multicast active] then the airplay targets appear.

So does seem to be a Multicast configuration problem.

It happens whether I use IGMP version 2 or version 3.