Running 4.1.185 in production with older Spectralink phones (NetLink i340/h340) - all is well. When I upgrade my backup controller to any 4.2 release (4.2.176 is the latest tried), SpectraLinks quit working - "No GW Response". This usually is a multicast issue, but cannot find the problem. Anyone run into this?
I found out that due to stricter handling of multicast in WLC/WiSM v4.2 and newer, it was necessary to enable PIM sparse-dense mode & ip multicast routing on the WiSM host switches for the SpectraLink VLAN *and* all the VLANs having APs... even though the phones and the NetLink gateways are in the same VLAN; strange to me, since SpectraLink SVP traffic is unroutable. Anyway, problem solved!
And for the benefit of others who may read this: There is also a new option for igmp snooping in the v4.2+ which must be turned on as part of the equation. (I'd already enabled it before my OP here.)