By Dev Tools Weekly | randommac.com
Format types, vendor prefixes, and everything about MAC addresses.
MAC Address Format
48 bits = 6 octets
┌───────────────────────┬───────────────────────┐
│ OUI (24 bits) │ NIC-specific (24 bits)│
│ Vendor/manufacturer │ Device unique ID │
└───────────────────────┴───────────────────────┘
Display Formats
| Format | Example | Common Use |
|---|
| Colon-separated | 00:1A:2B:3C:4D:5E | Linux, macOS |
| Hyphen-separated | 00-1A-2B-3C-4D-5E | Windows |
| Dot-separated | 001A.2B3C.4D5E | Cisco IOS |
| No separator | 001A2B3C4D5E | Programming, databases |
| IEEE canonical | 00:1A:2B:3C:4D:5E | Standards docs |
Special Bits (First Octet)
Bit 0 (LSB): Unicast vs. Multicast
| Bit 0 | Type | Meaning |
|---|
0 | Unicast | Single destination device |
1 | Multicast | Multiple destinations |
Bit 1: Universally vs. Locally Administered
| Bit 1 | Type | Meaning |
|---|
0 | UAA | Globally unique (assigned by IEEE) |
1 | LAA | Locally administered (set by admin/software) |
Quick Check
First octet in binary: XXXXXXML
│└─ 0=Unicast, 1=Multicast
└── 0=Universal, 1=Local
Hex examples:
00 = 0000 0000 → Unicast, Universal ✅ (normal)
02 = 0000 0010 → Unicast, Local (randomized/VM)
01 = 0000 0001 → Multicast, Universal
03 = 0000 0011 → Multicast, Local
Common OUI Vendor Prefixes
Networking Equipment
| OUI | Vendor |
|---|
00:00:0C | Cisco |
00:1B:17 | Cisco (alt) |
00:26:CB | Cisco (alt) |
00:1E:BD | Cisco (alt) |
00:04:96 | Juniper Networks |
00:05:85 | Juniper (alt) |
B4:A9:FC | Arista |
00:1C:7F | Check Point |
00:1A:8C | Sophos |
Consumer Devices
| OUI | Vendor |
|---|
00:03:93 | Apple |
3C:22:FB | Apple |
A4:83:E7 | Apple |
F0:18:98 | Apple |
00:15:5D | Microsoft (Hyper-V) |
00:50:56 | VMware |
08:00:27 | Oracle VirtualBox |
52:54:00 | QEMU/KVM |
00:16:3E | Xen |
IoT / Smart Home
| OUI | Vendor |
|---|
B0:BE:76 | TP-Link |
DC:A6:32 | Raspberry Pi |
24:6F:28 | Espressif (ESP32/ESP8266) |
30:AE:A4 | Espressif (alt) |
50:02:91 | Amazon (Echo/Ring) |
FC:65:DE | Google (Nest) |
Mobile
| OUI | Vendor |
|---|
8C:79:F5 | Samsung |
00:21:19 | Samsung (alt) |
E8:6F:38 | Xiaomi |
34:80:B3 | Xiaomi (alt) |
6C:21:A2 | OnePlus |
40:4E:36 | Huawei |
Broadcast & Special Addresses
| Address | Purpose |
|---|
FF:FF:FF:FF:FF:FF | Broadcast (all devices on segment) |
01:00:5E:xx:xx:xx | IPv4 multicast |
33:33:xx:xx:xx:xx | IPv6 multicast |
01:80:C2:00:00:00 | STP (Spanning Tree Protocol) |
01:80:C2:00:00:0E | LLDP |
01:00:0C:CC:CC:CC | Cisco CDP |
00:00:00:00:00:00 | Unspecified / null |
MAC Randomization (Privacy)
Modern OSes randomize MAC addresses to prevent tracking:
| OS | Behavior |
|---|
| iOS 14+ | Random MAC per Wi-Fi network (default on) |
| Android 10+ | Random MAC per network (default on) |
| Windows 10/11 | Random MAC per network (opt-in) |
| macOS 15+ | Private Wi-Fi Address (default on) |
| Linux | NetworkManager supports randomization |
Identifying randomized MACs: Look for bit 1 of first octet = 1 (locally administered).
Common randomized first octets: x2, x6, xA, xE (where x is any hex digit).
EUI-64 (IPv6 Interface ID)
Convert a 48-bit MAC to a 64-bit EUI-64 for IPv6:
- Split MAC in half:
00:1A:2B | 3C:4D:5E - Insert
FF:FE in the middle: 00:1A:2B:FF:FE:3C:4D:5E - Flip bit 1 of first octet (U/L bit):
02:1A:2B:FF:FE:3C:4D:5E
Result: 021A:2BFF:FE3C:4D5E → used in link-local fe80::21a:2bff:fe3c:4d5e
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