Abstract: A network interface for a connection-based communication network has support for message processing, including an interface for communication with an optional message coprocessor that performs a variety of message processing operations. Message processing is low level processing of messages between the host computer and the network. Such processing is performed on transmission in response to control information provided by the host and is performed on reception in response to control information included in incoming messages. Message processing includes low latency remote read and remote write operations, message filtering, and message demultiplexing. Such a network interface provides support for a variety of message processing operations using the coprocessor, while the complexity and cost of the network interface due to this support is minimal. The network interface provides control information for a message to the message coprocessor.