I was, finally, able to solve my problem. I didn't use your advice with alive but I guess it would have been a way to work around it.
My problem was that I was running mediatomb within http://linux-vserver.org/ as a guest; with the default settings mediatomb was able to send out multicast requests but wasn't able to properly receive them. E.g. when I turn on the TV, the TV sends out a multicast to find devices: because the guest system never forwarded that message, mediatomb never received it, thus didn't respond and thus didn't show up on my TV.
All I had to do was to add a separate multicast interface to my vserver.
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I was, finally, able to solve my problem. I didn't use your advice with alive but I guess it would have been a way to work around it.
My problem was that I was running mediatomb within http://linux-vserver.org/ as a guest; with the default settings mediatomb was able to send out multicast requests but wasn't able to properly receive them. E.g. when I turn on the TV, the TV sends out a multicast to find devices: because the guest system never forwarded that message, mediatomb never received it, thus didn't respond and thus didn't show up on my TV.
All I had to do was to add a separate multicast interface to my vserver.