This Counter32 counts the number of times an openSession() request failed specifically because the device could not open the underlying transport connection or could not authenticate the SSH server it was connecting to. Admins use this to distinguish transport/server-authentication failures from the later, more specific failure categories (user auth, channel, subsystem) tracked by other counters in this table. For example, a rise in this counter alongside no change in snmpSshtmSessionUserAuthFailures would point an admin toward a network reachability issue or a changed/untrusted SSH host key on the target server.