Media Access Control (MAC) addresses uniquely identify network interfaces, but they can be written in several different formats. This guide explains the various MAC address notation systems, their standards, and how to convert between them.
Common MAC Address Formats
A MAC address consists of 48 bits (6 bytes) represented as 12 hexadecimal digits. These digits can be grouped and separated in different ways depending on the context, device manufacturer, or software displaying them.
IEEE 802 Colon Format
The most common format uses colons to separate each byte (2 hex digits). This is the standard format used in most documentation and networking tools.
IEEE 802 Hyphen Format
Very similar to the colon format but uses hyphens as separators. Common in Microsoft Windows and some network documentation.
Cisco Format
Cisco networking equipment uses a format with three groups of four hexadecimal digits separated by dots.
Raw Hexadecimal
A continuous string of 12 hexadecimal digits without any separators. Often used in programming and database storage.
MAC Address Structure
Regardless of formatting, a MAC address always consists of 48 bits divided into two parts:
| Component | Size | Description |
|---|---|---|
| OUI (Organizationally Unique Identifier) | 24 bits (3 bytes) | The first half identifies the manufacturer of the network interface. Assigned by the IEEE Registration Authority. |
| Device Identifier | 24 bits (3 bytes) | The second half is a unique identifier assigned by the manufacturer. |
For example, in the MAC address 00:1A:2B:3C:4D:5E:
- 00:1A:2B is the OUI (manufacturer identifier)
- 3C:4D:5E is the device identifier (unique to the specific device)
Special Bits in MAC Addresses
The first byte of a MAC address contains two special bits with specific meanings:
-
Universal/Local (U/L) Bit - The second-least significant bit of the
first byte:
- 0 = Universally administered address (UAA) - Assigned by the manufacturer
- 1 = Locally administered address (LAA) - Assigned by a network administrator
-
Individual/Group (I/G) Bit - The least significant bit of the first
byte:
- 0 = Individual address (unicast)
- 1 = Group address (multicast)
Special MAC Addresses
Some MAC addresses have special purposes and reserved meanings:
| MAC Address | Format | Purpose |
|---|---|---|
| FF:FF:FF:FF:FF:FF | Broadcast | Used to send packets to all devices on a network |
| 01:00:5E:xx:xx:xx | IPv4 Multicast | Reserved for IPv4 multicast groups |
| 33:33:xx:xx:xx:xx | IPv6 Multicast | Reserved for IPv6 multicast groups |
| 01:80:C2:00:00:00 | Spanning Tree | Used by Spanning Tree Protocol (STP) |
| 00:00:00:00:00:00 | Zero Address | Used in some contexts to indicate an unspecified or invalid address |
Brand-Specific MAC Address Formats
Different manufacturers and operating systems may display MAC addresses in specific formats:
| Brand/OS | Common Format | Example |
|---|---|---|
| Microsoft Windows | Hyphen-separated | 00-1A-2B-3C-4D-5E |
| macOS/Linux | Colon-separated | 00:1A:2B:3C:4D:5E |
| Cisco IOS | Dot-separated (4 digits per group) | 001A.2B3C.4D5E |
| Juniper | Colon-separated | 00:1A:2B:3C:4D:5E |
| IBM | Period-separated | 00.1A.2B.3C.4D.5E |
Case Sensitivity in MAC Addresses
MAC addresses can be written using either uppercase or lowercase hexadecimal digits:
- Uppercase: 00:1A:2B:3C:4D:5E
- Lowercase: 00:1a:2b:3c:4d:5e
Both formats are functionally identical. By convention, official documentation often uses uppercase, while many software tools display addresses in lowercase. For MAC address lookup and storage, the case is typically not significant.
MAC Address Format in IPv6
When used in IPv6 addressing, MAC addresses are expanded to 64 bits using the EUI-64 (Extended Unique Identifier-64) format:
- The original 48-bit MAC address is split in the middle
- The value FF:FE is inserted between the halves
- The seventh bit (Universal/Local bit) is flipped
Example conversion from MAC to EUI-64:
- Original MAC: 00:1A:2B:3C:4D:5E
- Split and insert: 00:1A:2B:FF:FE:3C:4D:5E
- Flip U/L bit: 02:1A:2B:FF:FE:3C:4D:5E
MAC Address Pitfalls
When working with MAC addresses, be aware of these common issues:
- Privacy Concerns: MAC addresses can be used to track devices across networks, which is why modern operating systems often implement MAC randomization for network scanning.
- MAC Spoofing: MAC addresses can be changed via software, which means they shouldn't be relied upon as the sole means of authentication.
- Virtual Interfaces: Virtual machines and containers often use software-generated MAC addresses that may not follow standard vendor allocation patterns.
How to Format MAC Addresses Correctly
When writing or displaying MAC addresses, follow these best practices:
- Use the appropriate format for your audience (colon format is most universal)
- Be consistent in your chosen separator and case style
- Always use all 12 hexadecimal digits (zero-pad if necessary)
- For maximum compatibility, use lowercase letters in programming contexts
- When sorting or indexing MAC addresses, consider using the raw format (no separators)
Converting Between MAC Address Formats
Converting between different MAC address formats is straightforward:
- Remove all existing separators (colons, hyphens, dots)
- If needed, convert to all uppercase or all lowercase
- Group the digits according to the desired format
- Add the appropriate separators
Our MAC address lookup tool automatically handles different input formats, allowing you to enter MAC addresses with or without separators, and in any common notation style.