Private IP addresses let millions of networks reuse the same addresses without conflict. Understanding the three RFC 1918 ranges—and when to use each—prevents VPN routing nightmares and scales your network design.
Every packet you send to 127.0.0.1 loops back before it reaches hardware—a forty-year-old design decision that powers local development, secures sensitive services, and proves your network stack works even when everything else is broken.
0.0.0.0 means 'listen everywhere' when binding servers, 'the default path' in routing tables, and 'I don't exist yet' during DHCP. Same digits, different meanings—context is everything.
The IPv4 address space carved out billions of addresses that will never route publicly. These reservations aren't administrative overhead—they're the architectural decisions that made private networks, NAT, and the modern Internet possible.
Link-local addresses reveal a philosophical divide: IPv4 uses them as emergency fallback when DHCP fails, while IPv6 made them mandatory—the foundation that router discovery, neighbor detection, and autoconfiguration all build upon.
Multicast breaks a fundamental assumption about networks: that serving more people costs more. With multicast, a Raspberry Pi can stream to a million viewers—because it only sends the stream once.
Anycast lets hundreds of servers share one IP address. The Internet's routing system delivers your request to whichever server is closest—not geographically, but in network terms. It's how DNS root servers, CDNs, and DDoS protection actually work.
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