IPv6 deployment crept past 50% on major carriers in 2024-2025. The 'IPv4 will run out' panic is decades old; the practical question now is whether your service needs to support IPv6 natively. The answer is usually yes.
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Where IPv6 is dominant
Mobile (T-Mobile, Verizon ~80%+ IPv6 native), German residential, Indian mobile. Cloud-to-cloud east-west often IPv6-only. Corporate networks lag heavily.
Dual-stack vs IPv6-only
Most public-facing services: dual stack. Backend services in IPv6-rich environments: increasingly IPv6-only. Don't ship IPv4-only in 2026 — you'll be CG-NAT-translated and broken on some carriers.
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Common gotchas
Logging with IP truncation breaks on IPv6 (16 bytes ≠ 4). Block lists keyed on /32 don't work for IPv6 (use /64). DNS rebinding protection often misses IPv6 records.
Dual-stack everywhere public-facing. IPv6-only for new backend networks. Audit IP-handling code for IPv6 width.