I Can't See Any Network Devices!
Ordinarily, you don't need to do anything to your routers to enable discovery of DLNA devices.
If 2player fails to discover devices on your network, and if you have already taken steps to ensured that those devices have been correctly configured, try rebooting your router. This often works, particularly with routers that are more than a couple of years old.
We have had reports that some older models of Netgear routers do require an additional configuration step. UPnP is used to communicate with, and remotely configure routers, as well as to stream media. On affected Netgear routers, disabling UPnP configuration of the router also disables UPnP and DLNA network traffic. If 2player fails to discover any devices on your network, you may be affected by this problem. Make sure your router's firmware is up to date. Enabling UPnP on your router may correct the issue.
DLNA uses IGMP multicasting when performing network discovery. Very old routers may not implement IGMP multicasting; but anything built in the last decade is almost certain to support IGMP.
If you are using an entry-level Wi-Fi router, and have a large number of active DLNA devices, the router may not have enough CPU power to keep up. The DLNA device discovery protocols are fairly chatty, the load that gets placed a router increases dramatically as the number of participating DLNA devices increases. The problem doesn't seem to be so much bandwidth, as it is memory amd CPU use when routing IGMP broadcast packets used by DLNA. As a point of reference, we discovered this while running 14 test devices on our lab network. There are three solutions to this. The easiest is to disable the 2player Media server on Android devices that you aren't using, and power down other DLNA devices that aren't being used. Advanced users may try assigning static IP addresses to devices on the network. This doesn't actually reduce load from DLNA discovery, but it does reduce load from Windows Rally Automatic IP assignment on Windows networks, which may free up enough horsepower to allow DLNA discovery to work. The third solution is to buy a more expensive router. High-end home routers have much better CPUs and can deal with much higher load when routing IGMP packets. We haven't had any problems since we upgraded our router to a dual-band Wireless N router with Gigabit LAN support, which is bit more expensive than garden variety routers, but not much more so.
DLNA is designed to run on home networks, not large corporate networks, or public internet. Advanced users with large home network may find the following information helpful. Ordinary home users should not encounter any of the following problems. In our experience, advanced home users may run home networks on extraordinary collections of hand-me-down and scavenged Enterprise-grade network hardware. You know who you are. Those who don't know who they are are advised to read no further.
By design, DLNA devices cannot communicate with other devices that are more than four router hops away. If you have a large home network, the 4-hop restriction may come into play. Some routers may consider a transition from Wi-Fi to LAN and vice-versa as a network hop, so it's posible to run out of network hops after routing through only two devices. At present, the only workaround for this is to re-partition your network so that media devices are on the same or adjacent subnets.
In addition, DLNA discovery works on local networks only, and discovery packets will not be transmitted from a local subnet to a public subnet. Routers are supposed to discard DLNA discovery packets that hop to any sub-net other than those in private network ranges (192.168.0.0/16, 10.0,0,0/24, and 172.16.0.0/20) . In that case, you may need to adjust the configuration of your network to allow DLNA devices to communicate. Ordinarily, there should be no problems routing DLNA discovery packets between local subnets in the private ranges, or routing discovery packets between devices on the same subnet. Enterprise-grade routers may allow you to selectively route IGMP local traffic over non-private address ranges; but this is pretty much unexplored (and more-or-less unsupported) territory. If you are trying to run DLNA over over subnets in non-private address ranges, be advised: here be wumpuses.