Dev & Computing · IPv4 与 IPv6 地址（IPv4 & IPv6） · Updated 2026-10-25
What Is IPv4 & IPv6 Addresses?
Definition
IPv4 is 32-bit (192.168.1.1), totaling ~4.3 billion addresses — globally exhausted by 2019, kept alive by NAT (many devices sharing one public IP). IPv6 is 128-bit (2408:8207:…:1) with 3.4×10^38 addresses. Private ranges: 10.x, 172.16-31.x, 192.168.x are LAN-only; 127.0.0.1 is loopback. CIDR /24 means the first 24 bits are network — equivalent to netmask 255.255.255.0.
Formula
IPv4 space = 2^32 ≈ 4.29×10⁹; a /24 holds 254 usable hosts
Worked Example
Many "public" home IPs are carrier NAT (100.64.x.x); a 192.168.1.0/24 LAN fits 254 devices (.0 network and .255 broadcast excluded).
Common Misconception
"192.168.x.x is a public address" — the three private ranges never route on the internet. "IPv6 is always faster" — performance is comparable on-path; its win is end-to-end reachability (no NAT) and abundance. And enabling IPv6 does not break IPv4 sites — dual-stack picks per connection.
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