ARP Command doesn't display all devices

I have a machine on my network that needs to create a list of all mac addresses connected to the network. This is running OSX when I run the arp command it doesn't always display everything connected sometimes only the broadcast (255.255.255.0). However if I run the command on the DHCP server everything gets displayed.

The DHCP server is running Zentyal Linux. Are there any option I need to enable to allow anyone to scan the network?

Many thanks

Solution 1:

mac adress is added to arp table only after you send something to that machine. That's why it is empty on common machine (no communication) and full on server (dhcp negotiation with clients).

Simple arp isn't suitable for what you trying to do