Appearance
MAC Addresses
A MAC address is a unique hardware identifier assigned to a Network Interface Card (NIC). It operates at Layer 2 (Data Link Layer) of the OSI model.
Format
- 48 bits long, written as 6 groups of 2 hex digits.
- Example:
AA:BB:CC:DD:EE:FF - First 3 bytes → OUI (Organizationally Unique Identifier) — identifies the manufacturer.
- Last 3 bytes → device-specific identifier.
Key Characteristics
- Burned-in at the factory (stored in NIC firmware) — also called BIA (Burned-In Address).
- Globally unique (in theory).
- Flat addressing — no hierarchy, unlike IP addresses.
- Can be spoofed in software despite being hardware-based.
How It's Used
- Used for communication within the same network (LAN).
- When a frame is sent, it contains source + destination MAC.
- Switches use MAC addresses to build their MAC address table and forward frames intelligently.
MAC vs IP
| Feature | MAC | IP |
|---|---|---|
| Layer | Layer 2 | Layer 3 |
| Scope | Local (LAN) | Global |
| Assigned by | Manufacturer | Network admin / DHCP |
| Changes? | No (usually) | Yes (dynamic) |
| Format | 48-bit hex | 32-bit (IPv4) / 128-bit (IPv6) |
Special MAC Addresses
FF:FF:FF:FF:FF:FF→ Broadcast (sent to all devices on LAN)01:xx:xx:xx:xx:xx→ Multicast