Skip to main content

Powershell DNS Utility script for querying MX, PTR and SPF records

One thing as an email administrator that I find myself doing a lot is using nslookup to track down various problems with receiving and sending email. Whether its using it to look up a MX record , or to see if someone has a reverse DNS entry or maybe look at a SPF record if I’m looking at a sender ID issue. Now while I like nslookup I do find this utility a little cumbersome and slow to use at times so I started looking into seeing if I could automate this a little with a script. Doing this from a script isn’t the easiest thing in the world Peter Bromberg and Bill Jamieson came up with a great C# class for doing DNS queries which I’ve adapted and modified to do the particular things that I wanted. Because this class uses some Win32 API functions I’ve used Jeffrey Snovers method from here to make use of these functions in Powershell.

So the code is a compilation of bits and pieces from the sources above with some of my own touches. I’ve added an extra A record lookup for each of the hostnames that are returned from the MX query. I’ve also added some routines into to lookup and display SPF records. As well as including other routines to format the IP address correctly to perform reverse lookups.

The script can basically do 4 types of queries it takes 2 command line parameters the first is the type of query (A,MX,PTR,SPF) and second is the IP or hostname an example of running it is



I’ve put a downloadable copy of the code here the code itself looks like.

param([String] $dnsqtype = $(throw "Please specify the DNS Query Type"),[String] $IpParam = $(throw "Please specify the IPaddress"))

function Compile-Csharp ([string] $code, [Array]$References) {

# Get an instance of the CSharp code provider
$cp = New-Object Microsoft.CSharp.CSharpCodeProvider

$refs = New-Object Collections.ArrayList
$refs.AddRange( @("${framework}System.dll",
"${PsHome}\System.Management.Automation.dll",
"${PsHome}\Microsoft.PowerShell.ConsoleHost.dll",
"${framework}System.Windows.Forms.dll",
"${framework}System.Data.dll",
"${framework}System.Drawing.dll",
"${framework}System.XML.dll"))
if ($References.Count -ge 1) {
$refs.AddRange($References)
}

# Build up a compiler params object...
$cpar = New-Object System.CodeDom.Compiler.CompilerParameters
$cpar.GenerateInMemory = $true
$cpar.GenerateExecutable = $false
$cpar.IncludeDebugInformation = $false
$cpar.CompilerOptions = "/target:library"
$cpar.ReferencedAssemblies.AddRange($refs)
$cr = $cp.CompileAssemblyFromSource($cpar, $code)

if ( $cr.Errors.Count) {
$codeLines = $code.Split("`n");
foreach ($ce in $cr.Errors) {
write-host "Error: $($codeLines[$($ce.Line - 1)])"
$ce | out-default
}
Throw "INVALID DATA: Errors encountered while compiling code"
}
}

$code = @'
namespace PAB.DnsUtils
{
using System;
using System.Collections;
using System.ComponentModel;
using System.Runtime.InteropServices;
public class Dns
{
public Dns()
{
}

[DllImport("Dnsapi", EntryPoint="DnsQuery_W", CharSet=CharSet.Unicode, SetLastError=true, ExactSpelling=true)]
private static extern Int32 DnsQuery([MarshalAs(UnmanagedType.VBByRefStr)]ref string sName, QueryTypes wType, QueryOptions options, UInt32 aipServers, ref IntPtr ppQueryResults, UInt32 pReserved);
[DllImport("Dnsapi", CharSet=CharSet.Auto, SetLastError=true)]
private static extern void DnsRecordListFree(IntPtr pRecordList, int FreeType);

public enum ErrorReturnCode
{
DNS_ERROR_RCODE_NO_ERROR = 0,
DNS_ERROR_RCODE_FORMAT_ERROR = 9001,
DNS_ERROR_RCODE_SERVER_FAILURE = 9002,
DNS_ERROR_RCODE_NAME_ERROR = 9003,
DNS_ERROR_RCODE_NOT_IMPLEMENTED = 9004,
DNS_ERROR_RCODE_REFUSED = 9005,
DNS_ERROR_RCODE_YXDOMAIN = 9006,
DNS_ERROR_RCODE_YXRRSET = 9007,
DNS_ERROR_RCODE_NXRRSET = 9008,
DNS_ERROR_RCODE_NOTAUTH = 9009,
DNS_ERROR_RCODE_NOTZONE = 9010,
DNS_ERROR_RCODE_BADSIG = 9016,
DNS_ERROR_RCODE_BADKEY = 9017,
DNS_ERROR_RCODE_BADTIME = 9018
}

private enum QueryOptions
{
DNS_QUERY_ACCEPT_TRUNCATED_RESPONSE = 1,
DNS_QUERY_BYPASS_CACHE = 8,
DNS_QUERY_DONT_RESET_TTL_VALUES = 0x100000,
DNS_QUERY_NO_HOSTS_FILE = 0x40,
DNS_QUERY_NO_LOCAL_NAME = 0x20,
DNS_QUERY_NO_NETBT = 0x80,
DNS_QUERY_NO_RECURSION = 4,
DNS_QUERY_NO_WIRE_QUERY = 0x10,
DNS_QUERY_RESERVED = -16777216,
DNS_QUERY_RETURN_MESSAGE = 0x200,
DNS_QUERY_STANDARD = 0,
DNS_QUERY_TREAT_AS_FQDN = 0x1000,
DNS_QUERY_USE_TCP_ONLY = 2,
DNS_QUERY_WIRE_ONLY = 0x100
}

public enum QueryTypes
{
DNS_TYPE_A = 1,
DNS_TYPE_CNAME = 5,
DNS_TYPE_MX = 15,
DNS_TYPE_TEXT = 16,
DNS_TYPE_SRV = 33,
DNS_TYPE_PTR = 12

}

[StructLayout(LayoutKind.Explicit)]
private struct DnsRecord
{
[FieldOffset(0)]
public IntPtr pNext;
[FieldOffset(4)]
public string pName;
[FieldOffset(8)]
public short wType;
[FieldOffset(10)]
public short wDataLength;
[FieldOffset(12)]
public uint flags;
[FieldOffset(16)]
public uint dwTtl;
[FieldOffset(20)]
public uint dwReserved;

// below is a partial list of the unionized members for this struct

// for DNS_TYPE_A records
[FieldOffset(24)]
public uint a_IpAddress;

// for DNS_TYPE_ PTR, CNAME, NS, MB, MD, MF, MG, MR records
[FieldOffset(24)]
public IntPtr ptr_pNameHost;

// for DNS_TXT_ DATA, HINFO, ISDN, TXT, X25 records
[FieldOffset(24)]
public uint data_dwStringCount;
[FieldOffset(28)]
public IntPtr data_pStringArray;

// for DNS_TYPE_MX records
[FieldOffset(24)]
public IntPtr mx_pNameExchange;
[FieldOffset(28)]
public short mx_wPreference;
[FieldOffset(30)]
public short mx_Pad;

// for DNS_TYPE_SRV records
[FieldOffset(24)]
public IntPtr srv_pNameTarget;
[FieldOffset(28)]
public short srv_wPriority;
[FieldOffset(30)]
public short srv_wWeight;
[FieldOffset(32)]
public short srv_wPort;
[FieldOffset(34)]
public short srv_Pad;

}

public static string[] GetRecords(string domain, string dnsqtype)
{
IntPtr ptr1 = IntPtr.Zero ;
IntPtr ptr2 = IntPtr.Zero ;
DnsRecord rec;
Dns.QueryTypes qtype = QueryTypes.DNS_TYPE_PTR;
switch(dnsqtype){
case "MX":
qtype = QueryTypes.DNS_TYPE_MX;
break;
case "PTR":
qtype = QueryTypes.DNS_TYPE_PTR;
break;
case "SPF":
qtype = QueryTypes.DNS_TYPE_TEXT;
break;
case "A":
qtype = QueryTypes.DNS_TYPE_A;
break;
}

if(Environment.OSVersion.Platform != PlatformID.Win32NT)
{
throw new NotSupportedException();
}

ArrayList list1 = new ArrayList();
int num1 = DnsQuery(ref domain, qtype, QueryOptions.DNS_QUERY_USE_TCP_ONLY|QueryOptions.DNS_QUERY_BYPASS_CACHE, 0, ref ptr1, 0);
if (num1 != 0)
{
if (num1 == 9003)
{
String[] emErrormessage = new string[1];
emErrormessage.SetValue("No Record Found",0);
return emErrormessage;
}
else
{
String[] emErrormessage = new string[1];
emErrormessage.SetValue("Error During Query Error Number " + num1 , 0);
return emErrormessage;
}
}
for (ptr2 = ptr1; !ptr2.Equals(IntPtr.Zero); ptr2 = rec.pNext)
{
rec = (DnsRecord) Marshal.PtrToStructure(ptr2, typeof(DnsRecord));
if (rec.wType == (short)qtype)
{
string text1 = String.Empty;
switch(qtype)
{
case Dns.QueryTypes.DNS_TYPE_A:
System.Net.IPAddress ip = new System.Net.IPAddress(rec.a_IpAddress);
text1 = ip.ToString();
break;
case Dns.QueryTypes.DNS_TYPE_CNAME:
text1 = Marshal.PtrToStringAuto(rec.ptr_pNameHost);
break;
case Dns.QueryTypes.DNS_TYPE_MX:
text1 = Marshal.PtrToStringAuto(rec.mx_pNameExchange);
string[] mxalookup = PAB.DnsUtils.Dns.GetRecords(Marshal.PtrToStringAuto(rec.mx_pNameExchange), "A");
text1 = text1 + " : " + rec.mx_wPreference.ToString() + " : " ;
foreach (string st in mxalookup)
{
text1 = text1 + st.ToString() + " ";
}

break;
case Dns.QueryTypes.DNS_TYPE_SRV:
text1 = Marshal.PtrToStringAuto(rec.srv_pNameTarget);
break;
case Dns.QueryTypes.DNS_TYPE_PTR:
text1 = Marshal.PtrToStringAuto(rec.ptr_pNameHost);
break;
case Dns.QueryTypes.DNS_TYPE_TEXT:
if (Marshal.PtrToStringAuto(rec.data_pStringArray).ToLower().IndexOf("v=spf") == 0)
{
text1 = Marshal.PtrToStringAuto(rec.data_pStringArray);
}
break;
default:
continue;
}
list1.Add(text1);
}
}

DnsRecordListFree(ptr2, 0);
return (string[]) list1.ToArray(typeof(string));
}
}
}

'@
if ($dnsqtype.ToUpper() -eq "PTR"){
$ipIpaddressSplit = $IpParam.Split(".")
if ($ipIpaddressSplit.length -eq 4){
$revipaddress = $ipIpaddressSplit.GetValue(3) + "." + $ipIpaddressSplit.GetValue(2) + "." + $ipIpaddressSplit.GetValue(1) + "." + $ipIpaddressSplit.GetValue(0) + ".in-addr.arpa"}
else
{"Error in IPaddress Format"
}
}
else {
$revipaddress = $IpParam
}
Compile-Csharp $code
$qrQueryresults = [PAB.DnsUtils.DNS]::GetRecords($revipaddress,$dnsqtype.ToUpper())
""
foreach ($qresult in $qrQueryresults) {
$qresult
}
""

Popular posts from this blog

Testing and Sending email via SMTP using Opportunistic TLS and oAuth in Office365 with PowerShell

As well as EWS and Remote PowerShell (RPS) other mail protocols POP3, IMAP and SMTP have had OAuth authentication enabled in Exchange Online (Official announcement here ). A while ago I created  this script that used Opportunistic TLS to perform a Telnet style test against a SMTP server using SMTP AUTH. Now that oAuth authentication has been enabled in office365 I've updated this script to be able to use oAuth instead of SMTP Auth to test against Office365. I've also included a function to actually send a Message. Token Acquisition  To Send a Mail using oAuth you first need to get an Access token from Azure AD there are plenty of ways of doing this in PowerShell. You could use a library like MSAL or ADAL (just google your favoured method) or use a library less approach which I've included with this script . Whatever way you do this you need to make sure that your application registration  https://docs.microsoft.com/en-us/azure/active-directory/develop/quickstart-register-

How to test SMTP using Opportunistic TLS with Powershell and grab the public certificate a SMTP server is using

Most email services these day employ Opportunistic TLS when trying to send Messages which means that wherever possible the Messages will be encrypted rather then the plain text legacy of SMTP.  This method was defined in RFC 3207 "SMTP Service Extension for Secure SMTP over Transport Layer Security" and  there's a quite a good explanation of Opportunistic TLS on Wikipedia  https://en.wikipedia.org/wiki/Opportunistic_TLS .  This is used for both Server to Server (eg MTA to MTA) and Client to server (Eg a Message client like Outlook which acts as a MSA) the later being generally Authenticated. Basically it allows you to have a normal plain text SMTP conversation that is then upgraded to TLS using the STARTTLS verb. Not all servers will support this verb so if its not supported then a message is just sent as Plain text. TLS relies on PKI certificates and the administrative issue s that come around certificate management like expired certificates which is why I wrote th

The MailboxConcurrency limit and using Batching in the Microsoft Graph API

If your getting an error such as Application is over its MailboxConcurrency limit while using the Microsoft Graph API this post may help you understand why. Background   The Mailbox  concurrency limit when your using the Graph API is 4 as per https://docs.microsoft.com/en-us/graph/throttling#outlook-service-limits . This is evaluated for each app ID and mailbox combination so this means you can have different apps running under the same credentials and the poor behavior of one won't cause the other to be throttled. If you compared that to EWS you could have up to 27 concurrent connections but they are shared across all apps on a first come first served basis. Batching Batching in the Graph API is a way of combining multiple requests into a single HTTP request. Batching in the Exchange Mail API's EWS and MAPI has been around for a long time and its common, for email Apps to process large numbers of smaller items for a variety of reasons.  Batching in the Graph is limited to a m
All sample scripts and source code is provided by for illustrative purposes only. All examples are untested in different environments and therefore, I cannot guarantee or imply reliability, serviceability, or function of these programs.

All code contained herein is provided to you "AS IS" without any warranties of any kind. The implied warranties of non-infringement, merchantability and fitness for a particular purpose are expressly disclaimed.