Network interface systems are disclosed comprising a bus interface system, a media access control system, a memory system, a security system for selectively encrypting outgoing data and decrypting incoming data, a checksum system for generating and verifying checksum values, and a segmentation system for selectively segmenting outgoing data, where the network interface system may be fabricated as a single integrated circuit chip. Methods are also provided for interfacing a host system with a network, in which checksum information is obtained from the host system, which is used to generate checksum values for outgoing data while the data is being stored in a network interface memory system.