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Can 'port' sensor check both LISTEN and ESTABLISHED ?



Does port sensor check both TCP status, 'LISTEN' and 'ESTABLISHED'?

Is it correct to check OPEN status of the port using the telnet protocol?

I am using a port sensor, which checks port 34506.
In PRTG, it has error message; 'Connection refused (socket error # 10061)'.
There is no firewall. It is clearly an OPEN port.

The following is the result of checking the port status with 'netstat' command on the device.

[root@localhost ~]# netstat -ano|grep 34506
tcp        0      0     ESTABLISHED 

port ports tcp-port

Created on May 26, 2021 1:39:01 AM

Last change on May 26, 2021 5:51:07 AM by  Felix Wiesneth [Paessler Support]

1 Reply



Hi there,

the "Port Sensor" will only work with "Listen" ports on the target machine. The sensor will remotely connect to the target port and checks if it is able to establish a connection.

Also note, that the port 34506 is an outgoing port from the linux host, you issued the "netstat" command on. Such port can never be used for incomming connections.

If you want to monitor "Established" connections, you would have to use a "SSH Script Advanced Sensor", with your own script, that evaluates the resuls from the "netstat" command.

Kind Regards,
Matthias Kupfer - Team Tech Support

Created on May 27, 2021 7:46:01 AM by  Matthias Kupfer [Paessler Support]

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