When trying to add the SMP server to a new CEM gateway it would fail with an error The underlying connection was closed: An unexpected error occurred on a send
The underlying connection was closed: An unexpected error occurred on a send
The had a firewall rule that was blocking the traffic
ITMS 8.5 RU3
The firewall rule was modified to allow the traffic to the SMP server.
In this case Wireshark showed three hops between the gateway and the SMP. The TLS handshake started and when the client hello was sent it was immediately followed by a RST. The time to live dropped by 1. This indicated that a device in the middle was sending the reset. After they reconfigured the firewall rule the problem was resolved. See the attached Wireshark screenshot.