New answers tagged arp
The first icmp packet is fail because host sends ARP request. If the destination host MAC is already in ARP cahce the device is not send this request.
Connect to the device via a crossover cable or on the same network segment (preferred) via a switch/hub and run a network sniffer (netmon/wireshark/tcpdump) in promiscuous mode to identify the MAC address of the black box.
If you can connect physically to the device, or at least to the same network segment, you might be able to use arp -a to show you the mac address table on your server.
Can you download Linux live CD, plug it into your Macintosh, and use dhcpd in Linux to get the MAC address? (sorry, would have put this in a comment after the previous comment, but I don't have enough reputation on this site yet... :)
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