The Tunnel/Mirror feature supports both TCP and UDP protocols for sending and receiving data. In normal network configurations, TCP is strongly recommended, even in data diode mode. TCP provides reliable ordered delivery of messages, error checking, connection state tracking, and congestion control.

To enable these features, TCP requires a bi-directional network flow (ACKs and window updates must flow back from the receiver to the sender). Some data diode hardware systems support TCP emulation. They can synthesize the protocol packets required for the sender to believe that its messages are arriving at the destination.

If your data diode hardware does not provide this kind of TCP support, then UDP must be used. However, UDP has no native reliability layer. Packets can be lost in transmission, leading to gaps in the data stream.

To make the UDP option as robust and resilient as possible, DataHub software implements a forward-only reliability layer consisting of pacing, interleaving redundant packet copies, and receiver-side reordering with bounded hold locks. Any packet loss will trigger a warning message in the DataHub Event Log.