Report: RUT956 Serial over IP (SSL/Client) fails to reconnect silent sessions after server restart

[Johnbrowe]

Device: RUT956 Firmware Version: RUT9M_R_00.07.18.3 Module: RS485 / Serial over IP

Description: I am using the RUT956 to connect a Fire Alarm system to an Azure server via Serial over IP (TCP Client + SSL).

The connection works perfectly on start of service. However, if the remote server (Docker container) restarts, the connection drops and the router fails to auto-reconnect, even though “Keep Alive” and “Reconnect Interval” are configured. The router remains in a disconnected state indefinitely.

Traffic: The connected device (a firealarm) is completely silent (0 bytes TX/RX) for long periods. It only sends data during an alarm. Therefore, the connection relies entirely on TCP Keep-Alives to detect drops. The issue seems specific to how the router handles reconnection for idle/silent SSL sockets.

Symptoms:

1. Server side restarts (TCP connection broken).

2. Router eventually detects the drop via Keep Alive probes (WebUI shows Connected servers: 0/1).

3. The Failure: The router stays disconnected indefinitely. It does not trigger the Reconnect Interval logic.

4. The Workaround (Proof of Bug): If I simply toggle off click “Save & Apply” then toggle on and click “Save & Apply” in the Serial Configuration (without changing any settings), the router connects immediately. This should prove the network, IP, and Certificates are valid.

Configuration:

• Mode: Client

• Protocol: TCP

• TLS/SSL: Enabled (Certificate based)

• Reconnect Interval: 30

• Inactivity Timeout: 0 (Disabled)

• Keep Alive: ON

  • Time: 60

  • Interval: 10

  • Probes: 3

Steps to Reproduce:

1. Establish a Serial over IP (SSL) connection to a remote server.

2. Ensure no data is being transmitted (Silent/Idle state).

3. Restart the remote server application to force a socket break. (docker restart [container])

4. Wait for the Keep Alive settings to detect the drop (approx 90s).

5. Observe that the router marks the server as disconnected (0/1) but never attempts to reconnect automatically.

6. Click “Save & Apply” → Observe immediate successful reconnection.

[Vilius]

Greetings, @Johnbrowe ,

Welcome to Teltonika Community!

Thank you for your report, I will pass it on to our R&D team.

Therefore, for troubleshooting purposes, we will require more sensitive information from your end, such as the troubleshoot file, which may contain passwords, public IP addresses, serial numbers, and such. To avoid leaking this information, we have sent you a form to fill out, which you will receive in your e-mail inbox that you have registered your account with in the forums. In the Ticket ID field of the form, please enter the ID of this thread, which is 16499.

Thank you,
V.