Quick Tip: Update Resource Records in Microsoft DNS using Powershell

One of the great things I like about the (not so) new Windows 2008 R2 Powershell modules is that we can now more easily manage the core Microsoft Networking services (DNS, DHCP). I want to share a little script I built that will add/update Host Records fed from a CSV file.

The Script

In the past automating this kind of thing was possible using a combination of WMI and VBS/Powershell and or batch scripting and using the famous DNSCMD. My script script will not work on any DNS server, you need to run Windows 2008 or later DNS, running against Windows 2003 DNS servers will yield strange/wrong results.

#sample csv file

#DNSName,IP,<other fields not used>
#foo.fabrikam.com,192.168.1.1,<other values, not used>

Param(
 [Parameter(Mandatory=$false)][System.String]$ResourceRecordFile = "C:\Temp\somefile.txt",
 [Parameter(Mandatory=$false)][System.String]$dnsserver = "DNS.constoso.com"
 )
import-module DNSServer

Write-Warning "This script updates DNS resource records in DNS based on information in a CSV file. Details are:`n
Using file $ResourceRecordFile as source file.`nMaking changes on DNS:$dnsserver`n
If you wish to cancel Press Ctrl+C,otherwise press Enter`n"
Read-Host

$HostRecordList = Import-csv $ResourceRecordFile

foreach ($dnshost in $HostRecordList) {
 $RR = $dnshost.DNSName.split(".")[0]
 $Zone = $dnshost.DNSName.Remove(0,$RR.length+1)
 [System.Net.IPAddress]$NewIP = [System.Net.IPAddress]($dnshost.IP)
 $OldObj = Get-DnsServerResourceRecord -Name $RR -ZoneName $Zone -RRType "A" -ComputerName $dnsserver -ErrorAction SilentlyContinue
 If ($OldObj -eq $null) {
 write-host -ForegroundColor Yellow "Object does not exist in DNS, creating entry now"
 Add-DnsServerResourceRecord -Name $RR -ZoneName $Zone -A -CreatePtr:$true -ComputerName $dnsserver -IPv4Address $NewIP
 }
 Else {
 $NewObj = Get-DnsServerResourceRecord -Name $RR -ZoneName $Zone -RRType "A" -ComputerName $dnsserver
 $NewObj.RecordData.Ipv4Address = $NewIP
 If ($NewObj -ne $OldObj) {
 write-host -ForegroundColor Yellow "Object to write different, making change in DNS"
 Set-DnsServerResourceRecord -NewInputObject $NewObj -OldInputObject $OldObj -ZoneName $Zone -ComputerName $dnsserver
 }
 }
 $OldObj = $null
 $NewObj = $null
 }

Learning Points

Running this script requires Windows 2008 R2 RSAT installed. As you can see, all the script needs is a CSV file with 2 columns called “hostname” and IP, containing the FQDN, and the DNS server you want to connect and make the changes.

Lines 17-18: This is where we’re extracting the short DNS name from the FQDN and the DNS zone name. Also we are converting the IP address to the format required for entry into DNS:

$RR = $dnshost.DNSName.split(".")[0]
$Zone = $dnshost.DNSName.Remove(0,$RR.length+1)
[System.Net.IPAddress]$NewIP = [System.Net.IPAddress]($dnshost.IP)

Lines 19-21: Here we try to resolve the DNS record, perhaps it already exists. We will use this information in the next lines…

$OldObj = Get-DnsServerResourceRecord -Name $RR -ZoneName $Zone -RRType "A" -ComputerName $dnsserver -ErrorAction SilentlyContinue

Lines 23:  To create a new Host record  (“A” type record). T he command is pretty straightforward:

Add-DnsServerResourceRecord -Name $RR -ZoneName $Zone -A -CreatePtr:$true -ComputerName $dnsserver -IPv4Address $NewIP

Lines 27-31: or To update an existing A record. No that there is a difference in how Set-DNSServerResourceRecord works compared to the ADD command. This one requires that we get the record, modify the IPV4Address field, then use it to replace the old object.

$NewObj = Get-DnsServerResourceRecord -Name $RR -ZoneName $Zone -RRType "A" -ComputerName $dnsserver
$NewObj.RecordData.Ipv4Address = $NewIP
If ($NewObj -ne $OldObj) {
write-host -ForegroundColor Yellow "Object to write different, making change in DNS"
Set-DnsServerResourceRecord -NewInputObject $NewObj -OldInputObject $OldObj -ZoneName $Zone -ComputerName $dnsserver
}

That’s about it. You can easily modify this script, so that you can pass the DNS server name from the CSV file (updating lots of records on multiple DNS servers) or updating multiple record type (A Records, CNAME Records). As always C&C is welcome.