IPv4-mapped IPv6 address for 100.64.0.1

100.64.0.1 is a CGNAT shared address

100.64.0.1 belongs to 100.64.0.0/10, the shared address space commonly used for carrier-grade NAT (CGNAT). Internet service providers can use this range between customer networks and their own NAT infrastructure.

This range is not public internet address space and it is not one of the RFC 1918 private ranges. A CGNAT address can be shared by many subscribers behind provider-managed address translation, which can affect inbound connections and logging.

If this appears as a WAN address on a consumer router, port forwarding may not provide an inbound public service because the provider controls another NAT layer. The mapped IPv6 value does not bypass that layer.

Its IPv4-mapped IPv6 representation is ::ffff:6440:1. The mapping preserves the IPv4 bits for IPv6-aware software, but it does not turn a CGNAT address into a public IPv6 endpoint.

Shared address space is defined by RFC 6598 and listed in the IANA IPv4 special-purpose registry.