IPv6-Only (and IPv6-Mostly) Network Design

This chapter examines the design of IPv6-only and IPv6-mostly networks, focusing on strategies to transition from IPv4. As IPv4 addresses become increasingly scarce and Internet connectivity demands grow, adopting IPv6-only is essential. However, the coexistence of legacy IPv4 systems and varying network device capabilities require tailored solutions. This chapter details practical approaches for deploying IPv6-only infrastructures, covering scenarios such as IPv6-only servers, IPv6-only clients (DHCPv6, SLAAC), IPv6-mostly clients coexisting with IPv4 systems, home broadband networks, and IPv4 connectivity via IPv6 (IPv4aaS). For each scenario, the chapter provides comprehensive solutions that address topology design, address configuration, routing protocols, DNS and firewall configurations, and communication process workflows. By presenting a structured transition roadmap, the chapter guides network architects in implementing IPv6-centric solutions while ensuring interoperability with existing IPv4 services.