Assignment 3.1 Powershell and DNS
Consider the following powershell one liner. We are asking the DNS Server on 192.168.4.4 to resolve the IP Address 192.168.3.100. It turns out this is the instructor's PC in FOSTER 202.
Extend the one liner by creating a powershell script that takes a network prefix, the dns server to use (one of the cyber.local dns servers).
Deliverable 1. Provide a screenshot similar to the one below showing the program run against the foster subnet. The simplistic run shown here, just increments the octet in the 192.168.3.0/24 from 1 to 254.
Running Scripts on the System is disabled!
In order to prevent malicious scripts from running on your system, PowerShell enforces an execution policy.
Restricted - Scripts won’t run. Period. (Default setting.)
RemoteSigned - Locally created scripts run. Scripts that were created on another machine won’t run unless they are signed by a trusted publisher.
AllSigned - Scripts (including locally created scripts) only run if signed by a trusted publisher.
Unrestricted - All scripts run regardless of who created them and whether they’re signed.
https://www.pdq.com/blog/writing-your-first-powershell-script/
Enable scripts on the system
Open powershell as aministrator
run
Set-ExecutionPolicy RemoteSigned
Write the powershell script
When writing scripts in windows just used notepad and then save the file with the correct file name, and to the correct directory.
param(
[Parameter(Mandatory = $true)]
[string]$NetworkPrefix,
[Parameter(Mandatory = $true)]
[string]$DNSServer
)
for ($i = 1; $i -le 254; $i++) {
$IPAddress = "$NetworkPrefix.$i"
try {
$result = Resolve-DnsName -Name $IPAddress -Server $DNSServer -ErrorAction stop
Write-Output "IP: $IPAddress - Hostname $($result.NameHost)"
} catch {
continue
}
}Parameter definition
paramBlock: This allows the script to accept input parameters when run.[Parameter(Mandatory = $true)]: Ensures that the user must provide these values when running the script.[string]$NetworkPrefix: Defines the first parameter as a string for the network prefix (e.g.,192.168.1).[string]$DNSServer: Defines the second parameter as a string for the DNS server (e.g.,8.8.8.8).paramBlock: This allows the script to accept input parameters when run.[Parameter(Mandatory = $true)]: Ensures that the user must provide these values when running the script.[string]$NetworkPrefix: Defines the first parameter as a string for the network prefix (e.g.,192.168.1).[string]$DNSServer: Defines the second parameter as a string for the DNS server (e.g.,8.8.8.8).
Loop to iterante through host IDS
forLoop: Iterates from 1 to 254, representing common host IDs in a /24 subnet.$iVariable: Represents the current host ID in the iteration.$IPAddress = "$NetworkPrefix.$i": Constructs the full IP address by appending the host ID to the network prefix (e.g.,192.168.1.1).
DNS Resolution with Error Handling
tryBlock: Attempts to run the DNS resolution and catches errors if they occur.Resolve-DnsName: A PowerShell cmdlet that queries DNS records for a given name or IP address.-Name $IPAddress: Specifies the IP address to resolve.-Server $DNSServer: Uses the provided DNS server for the query.-ErrorAction Stop: Forces the cmdlet to throw an error if the resolution fails, triggering thecatchblock.
Out the Result if DNS Record Exists
Write-Output: Displays the resolved IP address along with the corresponding hostname.$result.NameHost: Extracts the hostname from the DNS resolution result.
Error Handling for Unresolved IPs
catchBlock: Executes if thetryblock encounters an error (i.e., if the DNS resolution fails).continue: Skips to the next iteration without printing any message, effectively suppressing output for IPs without DNS records.
Deliverable 2. Provide a screenshot similar to the one below that shows your directory structure and the source code of your powershell dns resolver. Alternatively, you can provide a link to your one liner in your github documentation.
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