Cisco IOS IPv6: Addressing, Routing Protocols, and Tunneling
Working reference for IPv6 on Cisco IOS. The 128-bit address format and compression rules, the five address scopes (loopback ::1/128, link-local fe80::/10 - automatic on every interface, ULA fc00::/7, GUA 2000::/3, multicast ff00::/8), the ipv6 unicast-routing global enable, three ways to set an interface address (manual, EUI-64 derived from MAC, SLAAC), static routing with ipv6 route, the four IPv6 routing protocols (OSPFv3 with the IPv4-format router-id quirk, EIGRPv6 which stays shutdown by default, RIPng, MP-BGP with its activate-in-address-family pattern), tunneling options (manual, GRE, 6to4, ISATAP), and the differences from IPv4 (no NAT, no ARP - replaced by NDP - no broadcast, multiple addresses per interface). Pitfalls: forgetting ipv6 unicast-routing, EIGRPv6 shutdown by default, missing BGP activate, routing protocols using link-locals you don't expect.