One or more I/O channels are assigned masks of message types that may pass through the channels, and one or more fields of an outbound message are set to one or more message type. A channel mask of an I/O channel is applied to a type of the outbound message, and if the channel mask matches the type of the outbound message, the outbound message is allowed to pass through the I/O channel to a switch. The outbound message is switched to an output port, and if the channel mask does not match the type of the outbound message, the outbound message is rejected from passing through the I/O channel and the channel mask of a next I/O channel is applied to the type of the outbound message.