Retrieve MAC addresses via SNMAP or ping sweep.

addresses.md

Using snmpwalk, this pulls the ARP table from the agent (e.g. router, switch):

snmpwalk -v 2c -c <community> <agent-ip> 1.3.6.1.2.1.4.22.1.2

OID: http://www.alvestrand.no/objectid/1.3.6.1.2.1.4.22.1.2.html

The ARP information might be stale though.

Using nmap ping-sweep:

sudo nmap -sP -n <ip>/24

Must be run as root, otherwise it won't return MAC addresses, just IPs.

See details: https://networkengineering.stackexchange.com/questions/6625/what-is-the-difference-between-ipnettomediaphysaddress-and-dot1qtpfdbport