If you want to get the mac addresses configured as different networks or subnetworks, but on the same phyiscal network the best way would be to query the switches on the network.

A couple of common commands for managed Cisco-like switches is
show mac address-table 
or
show bridge address-table

but it depends on your switch, and I am sure other switches use other commands...

Best if you run on all switches, as if two devices talk a lot to each other but nothing else, then only the switches those packets go through will likely show the address being used.

Another option if you can't query all the switches, would be to run
tcpdump -en -i eth0 -- broadcast

and wait awhile and parse all the results...  should probably run for at least 30 minutes, but possibly longer if default arp expiration is larger or are automatically renewed on traffic...



----- Original Message -----
> From: "ToddAndMargo" <[log in to unmask]>
> To: "Scientific Linux Users" <[log in to unmask]>
> Sent: Sunday, July 27, 2014 2:36:26 AM
> Subject: How do I discover all the MAC address on my Ethernet?
> 
> Hi All,
> 
> I have been Duck Duck Go'ing looking for how to discover
> all the mac addresses on my Ethernet.
> 
> http://www.linuxinternetworks.com/how-to-find-out-all-mac-address-on-network/
> 
> Says to do:  nmap -sP 192.168.1.0-255
> 
> Done that before and it does give you all the mac addresses
> on 192.168.1.0/24, but it does not give you mac addresses
> for those devices with different network configuration
> on your Ethernet.  (Like a stray access point on
> 192.168.88.0/24 on your Ethernet.)
> 
> I have tried these guys' java script:
>      http://www.ubnt.com/downloads/discovery/ubnt-discovery-v2.3.zip
> It runs but doesn't find anything.   Ran it in an XP VM too
> and it struck out there either.
> 
> Does anyone know how to get all the mac addresses on your
> Ethernet, even the ones configured on another network?
> 
> Many thanks,
> -T
>