Beijing IpPlusPlus Network Technology Co., Ltd. This memo proposes an extension scheme for IPv4. It can resolve the exhaustion of IPv4 addresses at an extremely low cost and enable external access to internal networks as convenient as internal access to external networks. IPv4 adopts 32-bit fixed-length addresses, the problem of insufficient address space has long been prominent. As a temporary solution, Network Address Translation (NAT) alleviates address scarcity to a certain extent, yet it breaks the end-to-end communication principle of the Internet. It only allows intranet devices to actively access the extranet and fails to support direct access from the extranet to the intranet. Although various solutions have been proposed in the industry, they all have inherent limitations. This paper presents an innovative scheme named IP++ based on multi-level variable-length addresses, which fundamentally solves the above problems and restores the IP protocol to the basic end-to-end principle. The multi-level variable-length address structure of IP++ is highly compatible with the natural hierarchical topology of the Internet, featuring strong backward compatibility, convenient deployment and excellent usability.