1.3. Addressing and Delivery: Finding and Reaching Destinations

💡 First Principle: Networks use two address types because they solve different problems. Physical addresses (MAC) identify hardware—they're burned in and never change. Logical addresses (IP) identify network location—they're assigned and change when devices move. Switches use MACs for local delivery; routers use IPs for remote delivery.

Think of it like identifying a person versus finding their location. A person's face (MAC) never changes, but their mailing address (IP) changes when they move. You need both to deliver a package—the face to verify identity, the address to find them.

What breaks without this understanding: You confuse switching with routing. You misconfigure subnet masks. You don't understand why ARP exists (it bridges the two address types). Most importantly, you can't troubleshoot "device can reach local hosts but not remote ones" because you don't understand where MAC-based delivery ends and IP-based routing begins.