Symptom
Sftunnel uses tls 1.3 for communication between FMC and FTD
Further Problem Description
Starting on 7.1 the firepower code supports tls 1.3 for communication channel/management channel as well as the event channel between FMC and Device(FTD). However both FTD and FMC must be on 7.1 or higher for this to apply and previous codes did not have support for tls 1.3
Do note that the initial registration TLS 1.2 will be offered as the FMC will not know the version of the FTD during registration and the FMC needs to be backwards compatible with code version not supporting tls 1.3. However if FTD supports tls 1.3 it will use the strongest available.
