Before the first hop, yes. However, when your packet crosses a routing device (firewall/router..) the mac is rewritten every hop with the mac of the routing device. So, if you were to sniff a packet on the "inside" of a router, you mac will read "3COM" or "INTEL" or whatever the make of your nic card is... however, if you sniff a packet on the "outside" of a router, and your router is a Cisco device, the mac will read "CISCO".