Gateways lose connection to server and Deduplication error

ChirpStack (v4)
1

Hi,
Our Chirpstack V4 environment always ran stable but since a week, for a few hours a day, mainly in the evening hours, some of the gateways lose connection to the server. Last seen status shows them as offline for some minutes, sometimes up to around 30 minutes. Most of them come back after the connection loss but individuals need a reset after this to come back online. Sometimes only individuals but at other times several gateways are effected and lose connection the same minute, but never all of them.
Using Semtech packet forwarder with gateway bridge on the server.
I cannot see any errors on the gateway bridge log and on the Chirpstack log the only error that appears is the following:

ERROR chirpstack::uplink: Deduplication error error=Unexpected m_type: UnconfirmedDataDown

I would appreciate any hint in regard of the gateway connection loss but also on how to find out what causes the Deduplication error. Thanks

2

You need to check the network connection between your gateway, gateway bridge and server.

This is not an issue.
The server rejects duplicated packets receiving from multiple gateways.
Likely you have multiple gateways hearing the same packets from the devices.

3

Hi datnus,
Thanks for your reply. Great to know that the deduplication error is not an issue!

Regarding the connection losses I cannot see any high network traffic on the server while this happens. One general question, do you know how many gateways and frequently transmitting sensors can be handled by one ChirpStack gateway bridge without getting problems?

4

1 server with 2 CPUs and 2 GB RAM can handle more than 100 gateways.
Of course, still need to know how many nodes and how frequent the uplinks?

Where do you install your Chirpstack server?

Is your network using unstable connection like 4G?

5

What type of gateway are you using? And what uphaul method (UDP to GW Bridge on server?)

Check the stats interval on your gateways, this is what determines the “offline” status on the server, whether the gateway sends stat messages in the timeframe Chirpstack expects. The default stats interval is 30 seconds so if your gateway is sending them every 30 minutes it would explain this.

While this isn’t a showstopper, It isn’t just a normal deduplication alert as @datnus suggests. It is an unexpected message type, and a confusing one at that, as it seems to suggest that Chirpstack received a downlink from a device. I don’t know what would cause that but as long as you don’t have too many devices I would try to isolate the device causing it. And if its not caused by a specific device it may be an error it Chirpstack itself.

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6

Hi datnus and Liam_Philipp,
Our server is better equipped than above and resources underutilized. Network traffic on the server is low according to Telegraf and there are no peaks to see during the problem phase. We use 4G connections and in the past did not have many issues with 4G.
Stats interval is standard 30 seconds. UDP connections to server gateway bridge.
The error message is from the ChirpStack log file. Difficult to isolate a device that could cause the message since there is nothing to see in the device event list of the console and the message comes very frequently. Perhaps @brocaar can step in here to bring some clarification?

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