Control point can't see library

[simoncn]

The network discovery protocol for UPnP devices requires multicast messaging across the network and it is the responsibility of the router (modem) to implement this. Unfortunately, some routers (modems) don't support multicast messaging or have a broken implementation. Other routers require certain configuration settings in order for multicast to work. In these cases, normal wireless traffic works OK but multicast messaging does not.

It is possible for some network switches to block multicast messaging by means of a feature called IGMP snooping. In your case, it seems that this doesn't apply as your PC is connected directly to the E2500.

Your router setting for Filter Multicast is correct. Pleae also check your UPnP settings. They should be as described in this post.

If this doesn't work, you could try configuring different SSIDs for the 2.4 GHz and 5 GHz wireless bands and connecting the iPad to each of these SSIDs to see if either of them works with multicast. Some routers support multicast on one of these frequencies but not the other.

If none of these ideas work, it is hard to know what else to suggest other than trying a different router.