MAC Address & Packets

MAC Address & Data Link Layer

MAC (Media Access Control) address is the addressing mechanism used when a message is traveling inside a LAN (Local Area Network).

• It is a hardware address burned into the network interface card (NIC).
• Written as 6 pairs of hex digits: 00:1A:2B:3C:4D:5E
• The first 3 pairs identify the manufacturer; the last 3 identify the device.

IP vs. MAC:

When data moves across a local network, the binary representation of the IP address is prefixed to the data as a header — this is how routers know where to send it next.

ARP (Address Resolution Protocol): When a device knows the IP address of a target but needs the MAC address to send a frame on the local network, it broadcasts an ARP request: “Who has IP 192.168.1.5?” The device with that IP replies with its MAC address.

Packets & How Data Travels

Packets are the collection of bits that travel across a network. Every packet contains:

• A header (IP address of source and destination, packet number, etc.)
• A payload (the actual data being sent)

Large messages are broken into multiple packets and reassembled at the destination.

        Original Message
   ┌──────────────────────────┐
   │         Data             │
   └──────────────────────────┘
              │
    Split into packets
              │
   ┌──────────┬──────────┬──────────┐
   │ Packet 1 │ Packet 2 │ Packet 3 │
   │IP add│Data│IP add│Data│IP add│Data│
   └──────────┴──────────┴──────────┘
              │
   Travel independently across the network
              │
   Reassembled at destination

Each packet may take a different route across the internet. This is by design — it makes the internet resilient. If one router fails, packets reroute automatically.