There is also a reverse ARP request, where a device provides a MAC address and asks “What IP address have you got?”.ĭevices can build up a cache of ARP responses so that they do not repeatedly ask for the same information. The device with the IP address responds with it’s MAC address and a message saying “I have that IP address”. On a local network, a device sends out a Address Resolution Protocol (ARP) request asking other devices on the network who has a certain IP address. NIC have MAC addresses, but most network addressing is done at Layer 3 (Network Layer) using IP addressing (IPv4 or IPv6). Ubuntu, Raspberry Pi OS)Īny virtualised network interfaces will also have a MAC address. Viewing MAC addresses (Debian Flavour Linux – e.g. Open a Terminal and type: ipconfig, the results should show each interface and an MAC address for each of them. Viewing MAC addresses (Microsoft Windows) Open a Terminal and type: ifconfig, the results should show each interface and an MAC address for each of them. The OUI can be used to identify the organisation that created the network interface, with tools such as the Wireshark OUI Lookup. The 48 bits are represented in hexadecimal. 3 octets (24 bits) are used to store the Organisationally Unique Identifier (OUI) and 3 octets (24 bits) are unique to the interface (i.e., in theory no two interfaces should have the same MAC address – more on this below).

MAC addresses work at Layer 2 (Data Link Layer) of the OSI (Open Systems Interconnection) model and are part of the IEEE (Institute of Electrical and Electronics Engineers) 802 standards.Ī MAC address is 48 bits split into 6 octets, with 8 bits per octet. A device may have multiple network interfaces (e.g., a ethernet network interface and a wireless network interface) and will a MAC address for each interface (e.g., a Rasperry Pi 4 has one MAC address for the ethernet and one MAC address for the wi-fi). Every network interface controller (NIC) has a Media Access Control (MAC) address which is unique to the interface.

Wireshark oui tool lookup