📘 03-01: MAC Addresses¶
❓ What Is a MAC Address?¶
A MAC (Media Access Control) address is a 48-bit Layer 2 physical address burned into every NIC. It is written as six pairs of hex digits:
- Also called a physical or hardware address.
- Used to deliver frames within a local network (broadcast domain).
📌 Structure¶
| First 24 bits (OUI) | Last 24 bits |
|---|---|
| Manufacturer ID (Organizationally Unique Identifier) | Device-specific serial |
- The OUI identifies the NIC vendor (assigned by IEEE).
- The remaining half is unique per device from that vendor.
📌 MAC vs. IP¶
| MAC address | IP address | |
|---|---|---|
| Layer | 2 (Data Link) | 3 (Network) |
| Scope | Local segment | End to end / global |
| Assigned by | Manufacturer (burned-in) | Admin / DHCP |
| Size | 48 bits | 32 (IPv4) / 128 (IPv6) |
| Changes when moved? | No | Yes (new network = new IP) |
Think MAC = who you physically are; IP = where you are on the network.
📌 ARP: Bridging IP and MAC¶
ARP (Address Resolution Protocol) resolves a known IP to its MAC on the local segment so frames can be delivered. In IPv6, this is handled by NDP (Neighbor Discovery). View the cache with arp -a.
Tip
Key idea — A MAC address is a 48-bit, vendor-assigned Layer 2 identifier (OUI + device ID). It delivers frames locally; ARP maps IP → MAC.
See also: IPv4 Addressing, CLI Troubleshooting Tools
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