Mike's PBX Cookbook

Finding a MAC address

Sometimes, we need to determine the hardware MAC address of a network interface, for example for an Avaya MAS keycode.
We can use ARP (Address Resolution Protocol) to do this. The following describes how, either from Mac OS X or Windows.

Note: This procedure will only work for devices on the same subnet as the computer doing the discovery.

  1. Either:
    • Mac OS X: Open a Terminal window.
    • Windows: Click Start -> Run, type cmd, and click Ok
  2. Type ping xxx.xxx.xxx.xxx, with the IP address of the device who's MAC address you want to find.
  3. Type ctrl-c to stop the ping.
  4. Type arp -a (to display all of the current ARP entries)
  5. The resulting output displays the IP address and a corresponding MAC address

The ARP table is cached, which is why a ping is needed to refresh it for that IP address entry.
To update the ARP table with all active network devices, ping the broadcast address (eg, x.x.x.255).

Example TTY Output:

Below we find the MAC address of device 10.5.3.68 is 00:F4:B9:32:28:19
mbp:~ mike$ ping 10.5.3.68      - ping the device
PING 10.5.3.68 (10.5.3.68): 56 data bytes
64 bytes from 10.5.3.68: icmp_seq=0 ttl=64 time=129.831 ms
64 bytes from 10.5.3.68: icmp_seq=1 ttl=64 time=138.959 ms
^C
--- 10.5.3.68 ping statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 129.831/134.395/138.959/4.564 ms
mbp:~ mike$ arp -a              - print the arp entries
? (10.5.0.4) at 0:50:e8:0:90:51 on en1 ifscope [ethernet]
? (10.5.1.232) at 24:77:3:7c:af:98 on en1 ifscope [ethernet]
? (10.5.3.68) at 0:f4:b9:32:28:19 on en1 ifscope [ethernet]     <- here it is!
? (10.5.255.255) at ff:ff:ff:ff:ff:ff on en1 ifscope [ethernet]
mbp:~ mike$ 

MAC / OUI lookup:

The first 3 octets of a MAC address uniquely identifies the hardware vendor, or manufacturer (OUI).
Enter a MAC address (or just the first 3 octets), hit submit, and macvendors should be able to identify it!

MAC:  (eg: '00:f4:b9' - any leading zero's are required)

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