This message primarily means that a TCP connection was initiated on a port that MassTransit was listening on (typically port 50000). After MassTransit has opened the socket, it begins to “probe” the remote destination for authentication. Here, it is determined whether the remote side is a legitimate MassTransit contact, and further, which contact is calling. If no information is passed during this “probing period,” the connection will eventually time out and produce this error message.

If you see this error message on a server or client that is not placing any calls, this is likely due to an activity monitor or port scanner that is opening a TCP connection on the MassTransit port. When your MassTransit listen does not receive any further expected data, it times out the connection with this error message.

If you see this error message while trying to place a call to a remote destination, this likely indicates some sort of transient network failure between the two endpoints. This can be due to extreme latency, or any other number of network factors that may account for a slow response from the remote server. In these cases, the problems generally correct themselves when the underlying problem is corrected.

In some cases, this may be due to a firewall or NAT problem. Your MassTransit server may establish a connection with a remote firewall or NAT, but the MassTransit packets are not properly forwarded on to a MassTransit endpoint. In that case, MassTransit also believes that the connection had been established, but is unable to receive any authentication data