PowerShell: Resolve Bulk IP Addresses to Hostnames

Posted on April 23, 2026 Updated on April 23, 2026

When you’re dealing with a large list of IP addresses from a firewall log or a network scan, manually running nslookup is not an option. You need a fast, automated way to perform a reverse DNS lookup to identify the devices on your network.

This script leverages the .NET [System.Net.Dns] class to perform high-speed lookups, converting a simple text file of IPs into a comma-separated list of hostnames.

The PowerShell Script

Save the code below as ResolveIPs.ps1. Create a file named hosts.txt in the same folder and paste your IP addresses (one per line).

PowerShell

# Get list from file, initialize empty array
$ListOfIPs = Get-Content ".\hosts.txt"
$ResultList = @()
# Roll through the list, resolving with the .NET DNS resolver
foreach ($IP in $ListOfIPs) {
    # Suppress errors for IPs that don't resolve
    $ErrorActionPreference = "silentlycontinue"
    $Result = $null
    # Status update for the user
    Write-Host "Resolving $IP..." -ForegroundColor Cyan
    
    # Pass the current IP to .NET for name resolution
    $Result = [System.Net.Dns]::GetHostEntry($IP)
    # Add results to the list
    if ($Result) {
        $ResultList += "$IP," + [string]$Result.HostName
    }
    else {
        $ResultList += "$IP,unresolved"
    }
}
# Export to file and notify completion
$ResultList | Out-File .\resolved.txt
Write-Host "Name resolution complete! Check .\resolved.txt" -ForegroundColor Green

How it Works

[System.Net.Dns]::GetHostEntry($IP): This is the heart of the script. It queries your configured DNS servers for a Pointer (PTR) record associated with the IP address.
Error Action Silencing: Since it’s common for some IPs (like guest devices or unmanaged switches) to lack DNS records, we use silentlycontinue to prevent the red error text from cluttering your console.
Array Building: The script creates a simple “IP,Hostname” format, which can easily be renamed to .csv and opened in Excel for further analysis.

💡 Lazy Admin Tips

DNS Suffixes: Ensure your machine has the correct DNS search suffixes configured. If the script only returns short names and you need FQDNs (Fully Qualified Domain Names), check your network adapter settings.
Speed: The .NET method used here is generally faster than the standard Resolve-DnsName cmdlet when dealing with large batches of legacy records.
Check Your PTRs: If the script returns “unresolved” for IPs you know are active, it’s a sign that your Reverse Lookup Zones in AD DNS might be missing records or need scavenging.

#PowerShell #Networking #DNS #SysAdmin #WindowsServer #Automation #ITPro #LazyAdmin #NetworkSecurity #TechTips