Each entry is phrased as the falsehood. Some of these may sometimes be true and sometimes be false. If I don’t have a RFC 1918 address, I’m not behind a NAT. Okay, only IP, IPX/SPX, Phase IV, AppleTalk, VINES, NetBEUI, or SNA are running on my LAN. MAC addresses are globally unique. (They’re supposed to be, but they aren’t.) The first three bytes are vendor‐unique if it’s a MA-L block.