Knowledge Base - WiFi Basics
      Back to home
      1. Help Center Home
      2. Knowledge Base - WiFi Basics

      Locally Administered MAC Address

      Locally administered addresses are distinguished from universally administered addresses by setting (assigning the value of 1 to) the second-least-significant bit of the first octet of the address.

      Locally Administered MAC Addresses (LAA) Explained

      A MAC address is a 48-bit identifier assigned to network interfaces. It consists of:

      • First 24 bits (OUI - Organizationally Unique Identifier): Assigned by the manufacturer (for Universally Administered Addresses, UAA)
      • Last 24 bits: Assigned by the manufacturer or dynamically modified in some cases

      How to Identify an LAA

      The U/L (Universal/Local) bit, located in the second-least-significant bit of the first octet, determines whether the address is locally or universally administered:

      • If U/L bit = 0, the MAC address is universally administered (UAA) (assigned by a manufacturer).
      • If U/L bit = 1, the MAC address is locally administered (LAA) (manually or dynamically assigned by software).

      For example:

      • Manufacturer-assigned MAC (UAA): 02:18:0A:12:34:56 → First octet 02 (binary: 00000010, U/L bit = 0)
      • Locally administered MAC (LAA): 06:18:0A:12:34:56 → First octet 06 (binary: 00000110, U/L bit = 1)

      How Cisco Meraki Uses LAA for BSSID MAC Addressing

      Cisco Meraki dynamically assigns BSSID MAC addresses using Locally Administered Addresses (LAA) to ensure unique SSIDs across an access point’s multiple virtual networks.

      Example: How Meraki Modifies MAC Addresses

      Meraki generates BSSID MAC addresses by modifying the AP’s base MAC address, incrementing specific octets:

      1. Base MAC Address (e.g., 00:18:0A:12:34:56)
      2. BSSID Calculation: The 4th octet increments for each SSID:
        • SSID 1: 00:18:0A:12:34:56
        • SSID 2: 00:18:0A:13:34:56
        • SSID 3: 00:18:0A:14:34:56
        • (continues for each SSID)

      Since these MAC addresses do not match a vendor-assigned OUI, they are classified as LAA.

      Why This Matters

      • Ensures unique BSSID MAC addresses for multiple SSIDs on the same AP.
      • Prevents conflicts with manufacturer-assigned MACs.
      • Supports cloud-managed Wi-Fi scalability.

      For more details, refer to Meraki’s BSSID MAC Calculation Guide.