Enable DLNA service discovery for media servers running on KVM hosts with bridged networking:

If you’re running a DLNA - capable Media Server (Such as Plex or Mediatomb) in a guest domain on a KVM/QEMU/libvirt-based hypervisor platform, make sure that the bridge you use to provide network access to the guest domain (such as macvtap) is configured in the host OS such that the allmulti flag is enabled. Assuming your bridge is macvtap0, you would sign into the host and go about setting the appropriate flag as follows:

$ sudo ip link set dev macvtap0 allmulticast on

Without this configuration, not all multicast packets required for DLNA (particularly client discovery operations) will be sent over the bridge to the guest domain, resulting in the media server failing to operate as required (because SSDP is not very forgiving).