MAC Address Lookup and Formatter — OUI Vendor Identification Tool

Our free MAC address lookup tool parses, formats and analyses any MAC address — converting between colon, dash and Cisco dot notation, identifying the OUI (Organisationally Unique Identifier) vendor prefix, and flagging special addresses like broadcast and multicast. Essential for network engineers troubleshooting ARP tables, DHCP leases, switch CAM tables and wireless client lists.

What is a MAC Address?

A MAC (Media Access Control) address is a unique 48-bit hardware identifier assigned to every network interface controller (NIC) by the manufacturer. It is used at the data link layer (Layer 2) of the OSI model to identify devices on a local network segment. Unlike IP addresses (which are logical and can be changed), MAC addresses are burned into hardware — though modern operating systems support MAC address randomisation for privacy protection on Wi-Fi networks.

MAC Address Structure

• First 3 bytes (OUI) — Organisationally Unique Identifier, assigned by the IEEE to hardware manufacturers. Example: 00:1A:2B is assigned to Cisco.
• Last 3 bytes (NIC-specific) — Unique identifier assigned by the manufacturer to the specific device
• Broadcast address — FF:FF:FF:FF:FF:FF — sent to all devices on the network segment
• Multicast addresses — First byte has LSB set to 1 (odd first octet) — e.g. 01:00:5E:xx:xx:xx for IPv4 multicast
• Locally administered — Second LSB of first byte set to 1 indicates a locally assigned (not manufacturer) MAC

MAC Addresses in Network Troubleshooting

• ARP table (arp -a) — Maps IP addresses to MAC addresses on the local subnet
• Switch CAM table — Shows which MAC addresses are reachable on each switch port
• DHCP leases — DHCP servers assign IPs based on MAC addresses — use for static IP assignments
• Wi-Fi client lists — Identify connected devices on access points
• Port security — Cisco switches can restrict which MAC addresses are allowed on a port