ipv6 route ::/0
Establishes an IPv6 static default route (the next-generation Gateway of Last Resort). The syntax ::/0 uses the zero-compression double colon to stand for an entirely blank prefix address alongside a prefix-length matching variable of zero bits. This matches every single outbound packet in existence if no more specific route is found in the IPv6 routing table.
Syntax Breakdown
CLI Deployment Scenarios
Scenario 1: Pointing to a Next-Hop Global Address
Forwarding all unmapped internet transit packets directly to an external provider GUA gateway.
Scenario 2: The Link-Local Next-Hop Necessity
If you choose to use a link-local address (FE80::) as your next-hop gateway address, Cisco IOS forces you to specify the local exit-interface as well. Because link-local addresses exist on every physical interface, the router won't know where to send the packet without an explicit exit interface.