Nowadays more and more IoT devices, including a large number of IoT servers, have been deployed on the Internet. The security of IoT servers has always been a challenge. In this paper, a new model named addressless IoT server is proposed, which allows people to use the large IPv6 address space to protect IoT server security. The server is allocated an IPv6 prefix instead of an address. When the authenticated client initiates communication, it uses an encryption mechanism to generate a specific destination address under the prefix. The server verifies the destination address when receiving the packet, and discards the packet if the verification fails. In this way, the model can prevent attackers from perceiving the server and launching scans or attacks, while remains compatible with the current Internet. The prototype is implemented and an extensive set of experiments are conducted in this paper. The results demonstrate that the model can better protect server security. INDEX TERMS IPv6, IPv6 address space, Internet of Things, network security, prefix delegation.