How to Use ARP to Find a MAC Address
In Windows, Linux, and other operating systems, the command line utility ARP (Address Resolution Protocol) shows local MAC address information stored in the ARP cache. However, it only works within the small group of computers on a local area network (LAN), not across the internet. ARP is intended to be used by system administrators, and it is not typically a useful way to track down computers and people on the internet. TCP/IP computer networks use both the IP addresses and MAC addresses of connected client devices. While the IP address changes over time, the MAC address of a network adapter always stays the same. Using ARP, each local network interface tracks both the IP address and MAC address for each device it has recently communicated with. Most computers let you see this list of addresses that ARP has collected. Here is one example of how to find a MAC address using an IP address.
Check Your Router’s Connection Data
To find the MAC address of the device connected to your router—assuming you can access the router’s administrative control panel—log in and check for connected devices. Each active device, as well as recently connected devices, should list the local IP address as well as the MAC address.
Why Figure Out a MAC Address?
A single device can possess multiple network interfaces and MAC addresses. A laptop computer with Ethernet, Wi-Fi, and Bluetooth connections, for example, has two or sometimes three MAC addresses associated with it, one for each physical network device. Reasons to track down the MAC address of a network device include:
To set up MAC address filtering on a router to restrict local network access to only those devices whose addresses match a list of presets. To determine the device’s manufacturer (first half of the address) and serial number (second half of the address) for service. It’s important to note that the second half of the address is not always the serial number, so it might not work for warranty requests. To masquerade (spoof) the identity of a different device. MAC addressing spoofing can be used legitimately to register a home network gateway device with an internet provider. It can also have malicious intent, such as defeating the MAC address filtering feature to break into the network.
Limitations of MAC Address Lookups
It isn’t usually possible to look up MAC addresses for devices outside a person’s physical reach. It is often impossible to determine a computer’s MAC address from its IP address alone because these two addresses originate from different sources. A computer’s hardware configuration determines its MAC address, while the network configuration it is connected to determines its IP address.
