The default port for SNMP is udp port 161
It requires the agent on the target device to be listening for a query.
What I would recommend is to check you PRTG is doing a query
You can test this on your machine by doing a trace
In a terminal
Do a query,
tcpdump -vvv -i any -s 1600 port 161
If you see output on the terminal that should indicate the packet going out.
You should see a response or responses coming back also
If you don't, either the query hit a machine which is not running an snmp agent , or the agent is not running, or their other machine is fire walled.
It could also be that your OID your using is not recognized, however, if the agent was running I would expect there to be some kind of response.
First things first though, run the trace and do the query
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