Resolve HostName from CNAME in PowerShell

Question

I have a network wherein CNAME entries are created for some servers and not for others. How can I get the details for server names alone by executing Resolve-DnsName script?

If I try

$servername = Resolve-DnsName -Name webserver.999.com
Write-Host $servername.Name

I get 2 results one with webserver.999.com and another with the actual server name post resolving the DNS for servers with CNAME, but only the server name where CNAME entry is not present. I am looking for a solution wherein the command catches the result with only the server name.

By "host name" do you mean the SMB Windows machine name?

Dai
– Dai

2018-07-20 22:53:52 +00:00
Commented Jul 20, 2018 at 22:53 — Dai
– Dai, Commented Jul 20, 2018 at 22:53
Yes, actual name of the server to which the CNAME points at

Rupesh
– Rupesh

2018-07-20 22:55:32 +00:00
Commented Jul 20, 2018 at 22:55 — Rupesh
– Rupesh, Commented Jul 20, 2018 at 22:55

Ansgar Wiechers · Accepted Answer · 2018-07-20 23:51:40Z

6

Select the result that is an A record:

Resolve-DnsName -Name foo.example.com |
    Where-Object { $_.QueryType -eq 'A' } |
    Select-Object -Expand Name

answered Jul 20, 2018 at 23:51

Ansgar Wiechers

202k27 gold badges286 silver badges363 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

mklement0 Over a year ago

I was going to suggestResolve-DnsName -Type A ... instead of Resolve-DnsName ... | Where-Object Type -eq A, but it seems that the former sometimes reports additional records of a different type; e.g., (Resolve-DnsName www.microsoft.com -Type A).Type Do you happen to know why?

Ansgar Wiechers Over a year ago

@mklement0 Nothing definitive. However, the call needs to resolve the entire chain of CNAMEs to get to the underlying A record, so I can see why it returns multiple results. After all, just responding that "www.microsoft.com" isn't an A record wouldn't be too useful from a name resolution perspective. It would make sense from a DNS management perspective, but there's a different set of cmdlets for that purpose.

mklement0 Over a year ago

Thanks, that makes sense; another thing that's perhaps of interest: it seems that such an indirect lookup of an A record only ever outputs one (as the last), whereas querying a name that directly has an A record can result in multiple A records for large sites (e.g., Resolve-DnsName microsoft.com -Type A).

TessellatingHeckler · Accepted Answer · 2018-07-20 23:54:58Z

2

To turn a CNAME into the original hostname:

Resolve-DnsName 'webserver.999.com' -Type CNAME |
    Select-Object -ExpandProperty 'NameHost'

answered Jul 20, 2018 at 23:54

TessellatingHeckler

29.3k4 gold badges55 silver badges96 bronze badges

1 Comment

Rupesh Over a year ago

This is not working if "webserver.999.com" doesn't have CNAME and "webserver.999.com" is the actual computer name

Mantvydas · Accepted Answer · 2022-10-21 14:55:26Z

0

One more way, which returns original hostname for a CNAME, original A name or just additional A name with the same IP of the server, as long as PTR records are maintained properly and point to the original hostname.

(resolve-dnsname (resolve-dnsname webserver.999.com).ipaddress ptr).namehost

answered Oct 21, 2022 at 14:55

Mantvydas

878 bronze badges

Comments

Tyler2P · Accepted Answer · 2023-09-11 11:27:59Z

PowerShell code to read CNAME records from a text file and output the original hostnames to another text file. Here's a script to do that:

# Specify the input and output file paths
$inputFilePath = "CNAMEs.txt"
$outputFilePath = "OriginalHostnames.txt"

# Read CNAMEs from the input file
$cnames = Get-Content -Path $inputFilePath

# Initialize an array to store the original hostnames
$originalHostnames = @()

# Iterate through each CNAME and resolve it to get the original hostname
foreach ($cname in $cnames) {
    $originalHostname = (Resolve-DnsName (Resolve-DnsName $cname).IPAddress PTR).NameHost
    $originalHostnames += $originalHostname
}

# Write the original hostnames to the output file
$originalHostnames | Out-File -FilePath $outputFilePath

# Display a message indicating the task is complete
Write-Host "Original hostnames have been written to $outputFilePath"

Collectives™ on Stack Overflow

Resolve HostName from CNAME in PowerShell

4 Answers 4

3 Comments

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

3 Comments

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related