HTTP sensor base on device IP

Not sure if the Paessler support will transition this request to a proper Feature request - but in any case - I like the idea you have there and since I am not aware of a solution for it that might already exist, I did a quick research.

What would work is a PowerShell script - I see if I might have time to work on it.. or you can do it on your own..

What you need is this:

https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.utility/invoke-webrequest?view=powershell-6

You will fire this command against the IP address, now, since the URL is part of the header of the web-request - specifically the HOST value in the HEADER.

You might run in to some resistance there - but I think there seems to be an interesting approach to bypass this here:

https://stackoverflow.com/questions/19937379/set-the-host-header-when-using-invoke-restmethod

There rest is just developing it out..

I doubt a DNS request wold give you all possible IPs from this round-robin configuration, especially not external DNS servers. Therefor you would need to inject all the IPs and the single target URL to the script, but that can be done via parameters...

Let me know if you need help - I generally suggest to try it on your own to learn at the same time..

PS: the Paessler Support Team might have better ideas and know about existing solutions.

Regards

Florian Rossmark

www.it-admins.com

The following is not yet the perfect script - but it might just work for you.

param(
    [string] $DomainName = "",
    [string] $IP = "",
    [string] $KeyWord = " ",
    [int] $MinimumResponseSizeInByte = 1,
    [bool] $useHTTPS = $true
)
add-type @"
    using System.Net;
    using System.Security.Cryptography.X509Certificates;
    public class TrustAllCertsPolicy : ICertificatePolicy {
        public bool CheckValidationResult(
            ServicePoint srvPoint, X509Certificate certificate,
            WebRequest request, int certificateProblem) {
            return true;
        }
    }
"@
[System.Net.ServicePointManager]::CertificatePolicy = New-Object TrustAllCertsPolicy

If ($useHTTPS -eq $true) { 
    $Prefix = "https://" 
} Else { 
    $Prefix = "http://" 
}

$IWRResponse = "";
$IWRError = 0;
$IWRErrorMessage = "";

$IWRResponse = Try {
    Invoke-WebRequest -Uri "$Prefix$IP" -Headers @{Host="$DomainName"} -ErrorAction Stop
} Catch {
    $IWRError = $_.Exception.GetHashCode()        
    If ($IWRError -eq 0) {
        $IWRError = 1 
    }
    $IWRErrorMessage = $_.Exception.Message
}
Try {
    $IWRResponse = $IWRResponse.ToString()
} Catch {}

$KeyWordFound = 0
Try {
    If ($IWRResponse.Contains($KeyWord)) { 
        $KeyWordFound = 1 
    } 
} Catch {}

$ResponseSufficient = 0 
Try {
    If ($IWRResponse -gt $MinimumResponseSizeInByte) { 
        $ResponseSufficient = 1 
    }  
} Catch {}

$XML = "<prtg>
    <result>
        <channel>Check result</channel>
        <value>$IWRError</value>
        <LimitMode>1</LimitMode>
        <LimitMinError>0</LimitMinError>
        <LimitMaxError>0</LimitMaxError>
        <LimitErrorMsg>$IWRErrorMessage</LimitErrorMsg>
    </result>
    <result>
        <channel>Keyword found</channel>
        <value>$KeyWordFound</value>
        <LimitMode>1</LimitMode>
        <LimitMinError>1</LimitMinError>
        <LimitErrorMsg>Keyword was not found in response</LimitErrorMsg>
    </result>
    <result>
        <channel>Response Length</channel>
        <value>" + $IWRResponse.Length + "</value>
        <VolumeSize>Byte</VolumeSize>
        <NotifyChanged>1</NotifyChanged>
    </result>
    <result>
        <channel>Reponse Length sufficient</channel>
        <value>$ResponseSufficient</value>
        <LimitMode>1</LimitMode>
        <LimitMinError>1</LimitMinError>
        <LimitErrorMsg>Response size not sufficient</LimitErrorMsg>
    </result>
</prtg>"

Function WriteXmlToScreen ([xml]$xml) #just to make it clean XML code...
{
    $StringWriter = New-Object System.IO.StringWriter;
    $XmlWriter = New-Object System.Xml.XmlTextWriter $StringWriter;
    $XmlWriter.Formatting = "indented";
    $xml.WriteTo($XmlWriter);
    $XmlWriter.Flush();
    $StringWriter.Flush();
    Write-Output $StringWriter.ToString();
}

WriteXmlToScreen "$XML"

In you case the following parameters would possibly work

-DomainName "app.test.local" -IP "192.168.10.10/login.html" -useHTTPs 0

If you add -Keyword "abcd" you can search for a keyword in the raw HTML response.

You could also engage the -MinimumResponseSizeInByt 999 parameter - while 999 bytes is just a guess of how much you should get back...

Let me know if it worked... of course you would need a sensor per target IP in this case - I did not develop it out to the extreme and the code could easily be optimized, just thought the idea of it is nice and it might be a start.

Regards

Florian Rossmark

www.it-admins.com