Offloading application level communication functions from a host processor. The offloading apparatus can be configured as either a pre-processor or as a co-processor. An interface is provided for receiving a network message sent to the host. An engine performs processing of the network message above OSI level 4. In one embodiment, in a fast-path, a response to the message is sent back to the network without any involvement by the host, providing a complete offload. For other messages, certain pre-processing can be performed, such as parsing of a header, message authentication, and look-up of meta-data. The results of the look-up are then passed to the host with the processed header, simplifying the tasks the host needs to perform. The messages and data are transferred to the host using control and data buffers.