Nmap not retrieving MAC address and Vendor

Question

I've found a strange behaviour in Nmap (I am using version 5.51 if that matters but I have the same issue with version 5.00), on some networks this plugin does not retrieve MAC address and, consequently, Vendor. The strange thing is that it retrieves almost everything like operating system and so on but it does not print the MAC address. How is that possible? This is the command I use usually:

nmap -A -O 192.168.1.0/24 -oX mynetwork.xml

Answer 1

The MAC address is only displayed when the scan is run with root privilege, so be sure to use sudo. As a diagnostic step, try doing a simple ping sweep (sudo nmap -sn 192.168.1.0/24), then immediately check your ARP cache (arp -an). If you don't see a lot of <incomplete>s, then Nmap isn't scanning your subnet properly. If you see 256 <incomplete>, and no MAC addresses, then something is wrong with your network setup, since you aren't seeing ARP responses to the requests Nmap is generating.