Knowledge Base

What to look for if an IPCheck sensor reports a "down" state

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You take great pride in running a flawlessly performing network, but then IPCheck Server Monitor reports that a sensor is down. It happens to the best of us. There are several reasons why a sensor might fail.

A common problem is related to faulty hardware -- a malfunctioning connection -- but if this possibility has been eliminated, a reason associated with the software can be tricky to track. Here is a quick checklist to keep on hand of what to go through if IPCheck Server Monitor reports a sensor failure somewhere on your network:

PING Sensor
The most common reason for a PING sensor to fail is that the sent packet did not reach the server, or the returning packet was not delivered back to the machine running IPCheck Server Monitor. Check the firewall between the server and the monitoring machine -- the firewall program may be rejecting packets because PINGs are not allowed under its rules. (When monitoring a remote server, a small amount of lost PINGs (1-2%) is usually considered not harmful.)

PORT Sensor
A down port sensor indicates a hardware or a server process issue. Check the connection and the service.

HTTP Sensor
Look for internal server errors ("error code 50x") and carefully check for incorrect URL addresses.

HTTP Advanced Sensor
Unfortunately, there are numerous possibilities. To locate the specific problem, it is best to examine the result string generated by IPCheck Server Monitor.

HTTP Transaction Sensor
Look for failed single requests, or timeouts for a single request or the complete sequence.

DNS Sensor
Four possibilities: 1) The DNS server cannot be reached because it is down. 2) The DNS server did not respond according to the protocol. 3) The domain name is invalid and could not be resolved. 4) The optional IP address is different from the IP resolved by the server.

SMTP Sensor
Check to see if the sensor's settings comply to the SMTP protocol, if it has been set to refuse email from a given domain/address, or if it simply has been set to refuse email. See the result string generated by IPCheck Server Monitor for more details.

POP3 Sensor
Check to see if the sensor has been set to comply to the POP3 protocol, if it has been set to not accept the login of a specific user, or if a user is not permitted to request a number of available mails. See the result string generated by IPCheck Server Monitor for more details.

FTP Sensor
The sensor does not comply with the FTP protocol or does not accept the login of the given user. See the result string generated by IPCheck Server Monitor for more details.

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