Expected response on ssdp:discover

[simoncn]

The expected response to the M-SEARCH multicast message is a unicast UDP message sent to the source IP address and port that was used to send the M-SEARCH request to the multicast address.

If you haven't set up routing between your subnets for unicast UDP messages, the media server can't open a connection to this IP address and port. This means the response message can't be sent, so you won't see see this message in any log.