Can You Find a MAC Address by Using an IP Address?

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TCP/IP computer networks use both the IP addresses and MAC addresses of connected client devices. A computer's assigned IP addresses change over time, but the MAC addresses of its network adapters stay the same.

Reasons Why It's Useful to Know a MAC Address

People may wish to track down the MAC address of a network device for a few reasons:

  • to determine the device's manufacturer (first half of the address) and serial number (second half of the address), such as for warranty service
  • to masquerade (spoof) the identity of a different device. MAC addressing spoofing can legitimately be used to register a home network gateway device with an Internet provider. Spoofing can also have illegitimate purposes such as defeating the MAC address filtering feature of a home network to break into it.
  • to help find the physical location of a device

Note that 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.

Limitations of MAC Address Lookup

Unfortunately, it isn't generally possible to look up MAC addresses for devices outside a person's physical reach.

 It often isn't possible to determine the MAC address of a computer from its IP address alone because these two addresses originate from different sources: A computer's own hardware configuration determines its MAC address while the configuration of the network it is connected to determines its IP address.

Computers connected to the same TCP/IP local network can determine each other's MAC addresses. The technology called ARP (Address Resolution Protocol) included with TCP/IP makes it possible. Using ARP, each local network interface tracks of both IP and MAC addresses for each device it has recently communicated with. Most computers allow you to see the list of IP and MAC addresses that ARP has collected there.

How to Use ARP

In Windows, Linux and other operating systems, the command line utility "arp" shows local MAC address information stored in the ARP cache. Using the ARP utility you can in fact determine the MAC address of some computers from their IP address. This works only within the small group of computers on a local area network (LAN), though, not across the Internet. ARP is intended for use by system administrators and is not generally useful as a way to track down computers and people on the Internet.