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1,For the SCCM client to remain active, it has to meet one of below five evaluation criteria defined in the Monitor\Client Status\Client Status Settings Properties in 7 days (by default). A client will be marked as inactive when all of these has not occurred within the last 7 days.
Client policy request
2,Client activity is based on communication from fast channel (Notification agent) which sends a keep-alive every 5 or 15 minutes depending on how the client is connected via fast channel (HTTP or TCP).
The notification agent (Client) will attempt to connect the TCP to the current management point using 10123 Port. Once it’s successful, the client will send the keep-alive message every 5 minutes by default through ClientNotificationAgent.log & CCMMessaging.log to MP.
If the client fails to establish a TCP Connection(Port 10123), the notification agent will try the HTTP protocol.
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