C# Signature:

    /// <summary>
    /// Provides a DNS query resolution interface
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682016(v=vs.85).aspx
    /// </summary>
    /// <param name="lpstrName">A pointer to a string that represents the DNS name to query</param>
    /// <param name="wType">A value that represents the Resource Record DNS Record Type that is queried</param>
    /// <param name="Options">A value that contains a bitmap of the DNS Query Options to use in the DNS query</param>
    /// <param name="pExtra">Reserved for future use and must be set to NULL</param>
    /// <param name="ppQueryResultsSet">A pointer to a pointer that points to the list of RRs that comprise the response</param>
    /// <param name="pReserved">Reserved for future use and must be set to NULL</param>
    /// <returns>Success (0), or the DNS-specific error defined in Winerror.h</returns>
    [DllImport("dnsapi", EntryPoint = "DnsQuery_W", CharSet = CharSet.Unicode, SetLastError = true, ExactSpelling = true)]
    public static extern int DnsQuery([MarshalAs(UnmanagedType.VBByRefStr)] ref string lpstrName, DnsRecordTypes wType, DnsQueryOptions Options, IntPtr pExtra, ref IntPtr ppQueryResultsSet, IntPtr pReserved);

    /// <summary>
    /// Frees memory allocated for DNS records obtained by using the DnsQuery function
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682021(v=vs.85).aspx
    /// </summary>
    /// <param name="pRecordList">A pointer to the DNS_RECORD structure that contains the list of DNS records to be freed</param>
    /// <param name="FreeType">A specifier of how the record list should be freed</param>
    [DllImport("dnsapi", CharSet = CharSet.Auto, SetLastError = true)]
    public static extern void DnsRecordListFree(IntPtr pRecordList, DNS_FREE_TYPE FreeType);

User-Defined Types:

C#

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/cc982162(v=vs.85).aspx
    /// </summary>
    [Flags]
    public enum DnsQueryOptions
    {
        DNS_QUERY_STANDARD = 0x0,
        DNS_QUERY_ACCEPT_TRUNCATED_RESPONSE = 0x1,
        DNS_QUERY_USE_TCP_ONLY = 0x2,
        DNS_QUERY_NO_RECURSION = 0x4,
        DNS_QUERY_BYPASS_CACHE = 0x8,
        DNS_QUERY_NO_WIRE_QUERY = 0x10,
        DNS_QUERY_NO_LOCAL_NAME = 0x20,
        DNS_QUERY_NO_HOSTS_FILE = 0x40,
        DNS_QUERY_NO_NETBT = 0x80,
        DNS_QUERY_WIRE_ONLY = 0x100,
        DNS_QUERY_RETURN_MESSAGE = 0x200,
        DNS_QUERY_MULTICAST_ONLY = 0x400,
        DNS_QUERY_NO_MULTICAST = 0x800,
        DNS_QUERY_TREAT_AS_FQDN = 0x1000,
        DNS_QUERY_ADDRCONFIG = 0x2000,
        DNS_QUERY_DUAL_ADDR = 0x4000,
        DNS_QUERY_MULTICAST_WAIT = 0x20000,
        DNS_QUERY_MULTICAST_VERIFY = 0x40000,
        DNS_QUERY_DONT_RESET_TTL_VALUES = 0x100000,
        DNS_QUERY_DISABLE_IDN_ENCODING = 0x200000,
        DNS_QUERY_APPEND_MULTILABEL = 0x800000,
        DNS_QUERY_RESERVED = unchecked((int)0xF0000000)
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/cc982162(v=vs.85).aspx
    /// Also see http://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml
    /// </summary>
    public enum DnsRecordTypes
    {
        DNS_TYPE_A = 0x1,
        DNS_TYPE_NS = 0x2,
        DNS_TYPE_MD = 0x3,
        DNS_TYPE_MF = 0x4,
        DNS_TYPE_CNAME = 0x5,
        DNS_TYPE_SOA = 0x6,
        DNS_TYPE_MB = 0x7,
        DNS_TYPE_MG = 0x8,
        DNS_TYPE_MR = 0x9,
        DNS_TYPE_NULL = 0xA,
        DNS_TYPE_WKS = 0xB,
        DNS_TYPE_PTR = 0xC,
        DNS_TYPE_HINFO = 0xD,
        DNS_TYPE_MINFO = 0xE,
        DNS_TYPE_MX = 0xF,
        DNS_TYPE_TEXT = 0x10,       // This is how it's specified on MSDN
        DNS_TYPE_TXT = DNS_TYPE_TEXT,
        DNS_TYPE_RP = 0x11,
        DNS_TYPE_AFSDB = 0x12,
        DNS_TYPE_X25 = 0x13,
        DNS_TYPE_ISDN = 0x14,
        DNS_TYPE_RT = 0x15,
        DNS_TYPE_NSAP = 0x16,
        DNS_TYPE_NSAPPTR = 0x17,
        DNS_TYPE_SIG = 0x18,
        DNS_TYPE_KEY = 0x19,
        DNS_TYPE_PX = 0x1A,
        DNS_TYPE_GPOS = 0x1B,
        DNS_TYPE_AAAA = 0x1C,
        DNS_TYPE_LOC = 0x1D,
        DNS_TYPE_NXT = 0x1E,
        DNS_TYPE_EID = 0x1F,
        DNS_TYPE_NIMLOC = 0x20,
        DNS_TYPE_SRV = 0x21,
        DNS_TYPE_ATMA = 0x22,
        DNS_TYPE_NAPTR = 0x23,
        DNS_TYPE_KX = 0x24,
        DNS_TYPE_CERT = 0x25,
        DNS_TYPE_A6 = 0x26,
        DNS_TYPE_DNAME = 0x27,
        DNS_TYPE_SINK = 0x28,
        DNS_TYPE_OPT = 0x29,
        DNS_TYPE_DS = 0x2B,
        DNS_TYPE_RRSIG = 0x2E,
        DNS_TYPE_NSEC = 0x2F,
        DNS_TYPE_DNSKEY = 0x30,
        DNS_TYPE_DHCID = 0x31,
        DNS_TYPE_UINFO = 0x64,
        DNS_TYPE_UID = 0x65,
        DNS_TYPE_GID = 0x66,
        DNS_TYPE_UNSPEC = 0x67,
        DNS_TYPE_ADDRS = 0xF8,
        DNS_TYPE_TKEY = 0xF9,
        DNS_TYPE_TSIG = 0xFA,
        DNS_TYPE_IXFR = 0xFB,
        DNS_TYPE_AFXR = 0xFC,
        DNS_TYPE_MAILB = 0xFD,
        DNS_TYPE_MAILA = 0xFE,
        DNS_TYPE_ALL = 0xFF,
        DNS_TYPE_ANY = 0xFF,
        DNS_TYPE_WINS = 0xFF01,
        DNS_TYPE_WINSR = 0xFF02,
        DNS_TYPE_NBSTAT = DNS_TYPE_WINSR
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682056(v=vs.85).aspx
    /// </summary>
    public enum DNS_FREE_TYPE
    {
        DnsFreeFlat = 0,
        DnsFreeRecordList = 1,
        DnsFreeParsedMessageFields = 2
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682082(v=vs.85).aspx
    /// These field offsets could be different depending on endianness and bitness
    /// </summary>

[StructLayout(LayoutKind.Sequential)]

    public struct DNS_RECORD
    {
    public IntPtr pNext;    // DNS_RECORD*
    public IntPtr pName;    // string
    public ushort wType;
    public ushort wDataLength;
    public FlagsUnion Flags;
    public uint dwTtl;
    public uint dwReserved;
    public DataUnion Data;
    }
    /* Below does not work in 64-bit Windows. Above works both in 32-bit and 64-bit Windows.

    [StructLayout(LayoutKind.Explicit)]
    public struct DNS_RECORD
    {
        [FieldOffset(0)]
        public IntPtr pNext;    // DNS_RECORD*
        [FieldOffset(4)]
        public IntPtr pName;    // string
        [FieldOffset(8)]
        public ushort wType;
        [FieldOffset(10)]
        public ushort wDataLength;
        [FieldOffset(12)]
        public FlagsUnion Flags;
        [FieldOffset(16)]
        public uint dwTtl;
        [FieldOffset(20)]
        public uint dwReserved;
        [FieldOffset(24)]
        public DataUnion Data;
    }

*/

    [StructLayout(LayoutKind.Explicit)]
    public struct FlagsUnion
    {
        [FieldOffset(0)]
        public uint DW;
        [FieldOffset(0)]
        public DNS_RECORD_FLAGS S;
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682084(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_RECORD_FLAGS
    {
        internal uint data;

        // DWORD Section :2;
        public uint Section
        {
        get { return data & 0x3u; }
        set { data = (data & ~0x3u) | (value & 0x3u); }
        }

        // DWORD Delete :1;
        public uint Delete
        {
        get { return (data >> 2) & 0x1u; }
        set { data = (data & ~(0x1u << 2)) | (value & 0x1u) << 2; }
        }

        // DWORD CharSet :2;
        public uint CharSet
        {
        get { return (data >> 3) & 0x3u; }
        set { data = (data & ~(0x3u << 3)) | (value & 0x3u) << 3; }
        }

        // DWORD Unused :3;
        public uint Unused
        {
        get { return (data >> 5) & 0x7u; }
        set { data = (data & ~(0x7u << 5)) | (value & 0x7u) << 5; }
        }

        // DWORD Reserved :24;
        public uint Reserved
        {
        get { return (data >> 8) & 0xFFFFFFu; }
        set { data = (data & ~(0xFFFFFFu << 8)) | (value & 0xFFFFFFu) << 8; }
        }
    }

    [StructLayout(LayoutKind.Explicit)]
    public struct DataUnion
    {
        [FieldOffset(0)]
        public DNS_A_DATA A;
        [FieldOffset(0)]
        public DNS_SOA_DATA SOA, Soa;
        [FieldOffset(0)]
        public DNS_PTR_DATA PTR, Ptr, NS, Ns, CNAME, Cname, DNAME, Dname, MB, Mb, MD, Md, MF, Mf, MG, Mg, MR, Mr;
        [FieldOffset(0)]
        public DNS_MINFO_DATA MINFO, Minfo, RP, Rp;
        [FieldOffset(0)]
        public DNS_MX_DATA MX, Mx, AFSDB, Afsdb, RT, Rt;
        [FieldOffset(0)]
        public DNS_TXT_DATA HINFO, Hinfo, ISDN, Isdn, TXT, Txt, X25;
        [FieldOffset(0)]
        public DNS_NULL_DATA Null;
        [FieldOffset(0)]
        public DNS_WKS_DATA WKS, Wks;
        [FieldOffset(0)]
        public DNS_AAAA_DATA AAAA;
        [FieldOffset(0)]
        public DNS_KEY_DATA KEY, Key;
        [FieldOffset(0)]
        public DNS_SIG_DATA SIG, Sig;
        [FieldOffset(0)]
        public DNS_ATMA_DATA ATMA, Atma;
        [FieldOffset(0)]
        public DNS_NXT_DATA NXT, Nxt;
        [FieldOffset(0)]
        public DNS_SRV_DATA SRV, Srv;
        [FieldOffset(0)]
        public DNS_NAPTR_DATA NAPTR, Naptr;
        [FieldOffset(0)]
        public DNS_OPT_DATA OPT, Opt;
        [FieldOffset(0)]
        public DNS_DS_DATA DS, Ds;
        [FieldOffset(0)]
        public DNS_RRSIG_DATA RRSIG, Rrsig;
        [FieldOffset(0)]
        public DNS_NSEC_DATA NSEC, Nsec;
        [FieldOffset(0)]
        public DNS_DNSKEY_DATA DNSKEY, Dnskey;
        [FieldOffset(0)]
        public DNS_TKEY_DATA TKEY, Tkey;
        [FieldOffset(0)]
        public DNS_TSIG_DATA TSIG, Tsig;
        [FieldOffset(0)]
        public DNS_WINS_DATA WINS, Wins;
        [FieldOffset(0)]
        public DNS_WINSR_DATA WINSR, WinsR, NBSTAT, Nbstat;
        [FieldOffset(0)]
        public DNS_DHCID_DATA DHCID;
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682044(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_A_DATA
    {
        public uint IpAddress;      // IP4_ADDRESS IpAddress;
        public System.Net.IPAddress IPAddressObject { get { return new IPAddress((long)IpAddress); } }
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682096(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_SOA_DATA
    {
        public IntPtr pNamePrimaryServer;       // string
        public IntPtr pNameAdministrator;       // string
        public uint dwSerialNo;
        public uint dwRefresh;
        public uint dwRetry;
        public uint dwExpire;
        public uint dwDefaultTtl;
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682080(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_PTR_DATA
    {
        public IntPtr pNameHost;    // string
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682067(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_MINFO_DATA
    {
        public IntPtr pNameMailbox;     // string
        public IntPtr pNameErrorsMailbox;       // string
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682070(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_MX_DATA
    {
        public IntPtr pNameExchange;        // string
        public ushort wPreference;
        public ushort Pad;
        public string NameExchange { get { return Marshal.PtrToStringAuto(pNameExchange); } }
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682109(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_TXT_DATA
    {
        public uint dwStringCount;
        public IntPtr pStringArray;     // PWSTR pStringArray[1];

        public List<string> Strings
        {
        get
        {
            List<string> res = new List<string>((int)dwStringCount);
            for ( int i = 0; i < dwStringCount; ++i )
            {
            IntPtr ptr = IntPtr.Add(pStringArray, i);
            string s = Marshal.PtrToStringUni(ptr);
            res.Add(s);
            }

            return res;
        }
        }

    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682074(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_NULL_DATA
    {
        public uint dwByteCount;
        public IntPtr Data;           // BYTE  Data[1];
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682120(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_WKS_DATA
    {
        public uint IpAddress;      // IP4_ADDRESS IpAddress;
        public byte chProtocol;     // UCHAR       chProtocol;
        public IntPtr BitMask;        // BYTE    BitMask[1];
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682035(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_AAAA_DATA
    {
        // IP6_ADDRESS Ip6Address;
        // DWORD IP6Dword[4];
        // This isn't ideal, but it should work without using the fixed and unsafe keywords
        public uint Ip6Address0;
        public uint Ip6Address1;
        public uint Ip6Address2;
        public uint Ip6Address3;
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682061(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_KEY_DATA
    {
        public ushort wFlags;
        public byte chProtocol;
        public byte chAlgorithm;
        public IntPtr Key;        // BYTE Key[1];
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682094(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_SIG_DATA
    {
        public IntPtr pNameSigner;      // string
        public ushort wTypeCovered;
        public byte chAlgorithm;
        public byte chLabelCount;
        public uint dwOriginalTtl;
        public uint dwExpiration;
        public uint dwTimeSigned;
        public ushort wKeyTag;
        public ushort Pad;
        public IntPtr Signature;      // BYTE  Signature[1];
    }

    public const int DNS_ATMA_MAX_ADDR_LENGTH = 20;
    public const int DNS_ATMA_FORMAT_E164 = 1;
    public const int DNS_ATMA_FORMAT_AESA = 2;

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682041(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_ATMA_DATA
    {
        public byte AddressType;
        // BYTE Address[DNS_ATMA_MAX_ADDR_LENGTH];
        // This isn't ideal, but it should work without using the fixed and unsafe keywords
        public byte Address0;
        public byte Address1;
        public byte Address2;
        public byte Address3;
        public byte Address4;
        public byte Address5;
        public byte Address6;
        public byte Address7;
        public byte Address8;
        public byte Address9;
        public byte Address10;
        public byte Address11;
        public byte Address12;
        public byte Address13;
        public byte Address14;
        public byte Address15;
        public byte Address16;
        public byte Address17;
        public byte Address18;
        public byte Address19;
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682076(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_NXT_DATA
    {
        public IntPtr pNameNext;    // string
        public ushort wNumTypes;
        public IntPtr wTypes;       // WORD  wTypes[1];
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682097(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_SRV_DATA
    {
        public IntPtr pNameTarget;      // string
        public ushort uPriority;
        public ushort wWeight;
        public ushort wPort;
        public ushort Pad;
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/cc982164(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_NAPTR_DATA
    {
        public ushort wOrder;
        public ushort wPreference;
        public IntPtr pFlags;       // string
        public IntPtr pService;     // string
        public IntPtr pRegularExpression;       // string
        public IntPtr pReplacement;     // string
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/dd392298(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_OPT_DATA
    {
        public ushort wDataLength;
        public ushort wPad;
        public IntPtr Data;           // BYTE Data[1];
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/dd392296(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_DS_DATA
    {
        public ushort wKeyTag;
        public byte chAlgorithm;
        public byte chDigestType;
        public ushort wDigestLength;
        public ushort wPad;
        public IntPtr Digest;         // BYTE Digest[1];
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/dd392301(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_RRSIG_DATA
    {
        public IntPtr pNameSigner;      // string
        public ushort wTypeCovered;
        public byte chAlgorithm;
        public byte chLabelCount;
        public uint dwOriginalTtl;
        public uint dwExpiration;
        public uint dwTimeSigned;
        public ushort wKeyTag;
        public ushort Pad;
        public IntPtr Signature;      // BYTE  Signature[1];
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/dd392297(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_NSEC_DATA
    {
        public IntPtr pNextDomainName;    // string
        public ushort wTypeBitMapsLength;
        public ushort wPad;
        public IntPtr TypeBitMaps;    // BYTE  TypeBitMaps[1];
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/dd392295(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_DNSKEY_DATA
    {
        public ushort wFlags;
        public byte chProtocol;
        public byte chAlgorithm;
        public ushort wKeyLength;
        public ushort wPad;
        public IntPtr Key;        // BYTE Key[1];
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682104(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_TKEY_DATA
    {
        public IntPtr pNameAlgorithm;   // string
        public IntPtr pAlgorithmPacket; // PBYTE (which is BYTE*)
        public IntPtr pKey;         // PBYTE (which is BYTE*)
        public IntPtr pOtherData;       // PBYTE (which is BYTE*)
        public uint dwCreateTime;
        public uint dwExpireTime;
        public ushort wMode;
        public ushort wError;
        public ushort wKeyLength;
        public ushort wOtherLength;
        public byte cAlgNameLength;     // UCHAR cAlgNameLength;
        public int bPacketPointers;     // BOOL  bPacketPointers;
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682106(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_TSIG_DATA
    {
        public IntPtr pNameAlgorithm;   // string
        public IntPtr pAlgorithmPacket; // PBYTE (which is BYTE*)
        public IntPtr pSignature;       // PBYTE (which is BYTE*)
        public IntPtr pOtherData;       // PBYTE (which is BYTE*)
        public long i64CreateTime;
        public ushort wFudgeTime;
        public ushort wOriginalXid;
        public ushort wError;
        public ushort wSigLength;
        public ushort wOtherLength;
        public byte cAlgNameLength;     // UCHAR    cAlgNameLength;
        public int bPacketPointers;     // BOOL     bPacketPointers;
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682114(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_WINS_DATA
    {
        public uint dwMappingFlag;
        public uint dwLookupTimeout;
        public uint dwCacheTimeout;
        public uint cWinsServerCount;
        public uint WinsServers;    // IP4_ADDRESS WinsServers[1];
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682113(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_WINSR_DATA
    {
        public uint dwMappingFlag;
        public uint dwLookupTimeout;
        public uint dwCacheTimeout;
        public IntPtr pNameResultDomain;    // string
    }

    /// <summary>
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/dd392294(v=vs.85).aspx
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    public struct DNS_DHCID_DATA
    {
        public uint dwByteCount;
        public IntPtr DHCID;          // BYTE  DHCID[1];
    }

Helper Functions:

    /// <summary>
    /// Converts an unsigned int to an ip address object
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/cc982163(v=vs.85).aspx
    /// </summary>
    /// <param name="ipAddress">The unsigned int to convert to an ip address object</param>
    /// <returns>The converted ip address</returns>
    public static IPAddress ConvertUintToIpAddress(uint ipAddress)
    {
        // x86 is in little endian
        // Network byte order (what the IPAddress object requires) is big endian
        // Ex - 0x7F000001 is 127.0.0.1
        var addressBytes = new byte[4];
        addressBytes[0] = (byte)((ipAddress & 0xFF000000u) >> 24);
        addressBytes[1] = (byte)((ipAddress & 0x00FF0000u) >> 16);
        addressBytes[2] = (byte)((ipAddress & 0x0000FF00u) >> 8);
        addressBytes[3] = (byte)(ipAddress & 0x000000FFu);
        return new IPAddress(addressBytes);
    }

    /// <summary>
    /// Converts the data from the AAAA record into an ip address object
    /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682140(v=vs.85).aspx
    /// </summary>
    /// <param name="data">The AAAA record to convert</param>
    /// <returns>The converted ip address</returns>
    public static IPAddress ConvertAAAAToIpAddress(DNS_AAAA_DATA data)
    {
        var addressBytes = new byte[16];
        addressBytes[0] = (byte)(data.Ip6Address0 & 0x000000FF);
        addressBytes[1] = (byte)((data.Ip6Address0 & 0x0000FF00) >> 8);
        addressBytes[2] = (byte)((data.Ip6Address0 & 0x00FF0000) >> 16);
        addressBytes[3] = (byte)((data.Ip6Address0 & 0xFF000000) >> 24);
        addressBytes[4] = (byte)(data.Ip6Address1 & 0x000000FF);
        addressBytes[5] = (byte)((data.Ip6Address1 & 0x0000FF00) >> 8);
        addressBytes[6] = (byte)((data.Ip6Address1 & 0x00FF0000) >> 16);
        addressBytes[7] = (byte)((data.Ip6Address1 & 0xFF000000) >> 24);
        addressBytes[8] = (byte)(data.Ip6Address2 & 0x000000FF);
        addressBytes[9] = (byte)((data.Ip6Address2 & 0x0000FF00) >> 8);
        addressBytes[10] = (byte)((data.Ip6Address2 & 0x00FF0000) >> 16);
        addressBytes[11] = (byte)((data.Ip6Address2 & 0xFF000000) >> 24);
        addressBytes[12] = (byte)(data.Ip6Address3 & 0x000000FF);
        addressBytes[13] = (byte)((data.Ip6Address3 & 0x0000FF00) >> 8);
        addressBytes[14] = (byte)((data.Ip6Address3 & 0x00FF0000) >> 16);
        addressBytes[15] = (byte)((data.Ip6Address3 & 0xFF000000) >> 24);

        return new IPAddress(addressBytes);
    }

Alternative Managed API:

Do you know one? Please contribute it!

Notes:

See original example provided by Peter A Bromberg, Ph.D.

http://www.eggheadcafe.com/articles/20050129.asp

New example provided by Dylan Jones (jonesdyn@gmail.com).

Tips & Tricks:

Please add some!

Sample Code:

C#

    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Net;
    using System.Runtime.InteropServices;

    namespace DnsTest
    {
    public class Dns
    {
        /// <summary>
        /// Returns a list of exchange server names from the MX records found from the given domain
        /// This function can be easily changed to return data from other DNS records
        /// </summary>
        /// <param name="domain">The domain to query for MX records</param>
        /// <returns>A list of exchange server names from the MX records found from the given domain</returns>
        public static List<string> GetMxRecords(string domain)
        {
        if (Environment.OSVersion.Platform != PlatformID.Win32NT)
        {
            throw new NotSupportedException();
        }

        var recordsArray = IntPtr.Zero;
        try
        {
            var result = DnsQuery(ref domain, DnsRecordTypes.DNS_TYPE_MX, DnsQueryOptions.DNS_QUERY_BYPASS_CACHE,
            IntPtr.Zero, ref recordsArray, IntPtr.Zero);
            if (result != 0)
            {
            throw new Win32Exception(result);
            }

            DNS_RECORD record;
            var recordList = new List<string>();
            for (var recordPtr = recordsArray; !recordPtr.Equals(IntPtr.Zero); recordPtr = record.pNext)
            {
            record = (DNS_RECORD)Marshal.PtrToStructure(recordPtr, typeof(DNS_RECORD));
            if (record.wType == (int)DnsRecordTypes.DNS_TYPE_MX)
            {
                recordList.Add(Marshal.PtrToStringAuto(record.Data.MX.pNameExchange));
            }
            }

            return recordList;
        }
        finally
        {
            if (recordsArray != IntPtr.Zero)
            {
            DnsRecordListFree(recordsArray, DNS_FREE_TYPE.DnsFreeFlat);
            }
        }
        }

        /// <summary>
        /// Provides a DNS query resolution interface
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682016(v=vs.85).aspx
        /// </summary>
        /// <param name="lpstrName">A pointer to a string that represents the DNS name to query</param>
        /// <param name="wType">A value that represents the Resource Record DNS Record Type that is queried</param>
        /// <param name="Options">A value that contains a bitmap of the DNS Query Options to use in the DNS query</param>
        /// <param name="pExtra">Reserved for future use and must be set to NULL</param>
        /// <param name="ppQueryResultsSet">A pointer to a pointer that points to the list of RRs that comprise the response</param>
        /// <param name="pReserved">Reserved for future use and must be set to NULL</param>
        /// <returns>Success (0), or the DNS-specific error defined in Winerror.h</returns>
        [DllImport("dnsapi", EntryPoint = "DnsQuery_W", CharSet = CharSet.Unicode, SetLastError = true,
        ExactSpelling = true)]
        public static extern int DnsQuery([MarshalAs(UnmanagedType.VBByRefStr)] ref string lpstrName, DnsRecordTypes wType,
        DnsQueryOptions Options, IntPtr pExtra, ref IntPtr ppQueryResultsSet, IntPtr pReserved);

        /// <summary>
        /// Frees memory allocated for DNS records obtained by using the DnsQuery function
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682021(v=vs.85).aspx
        /// </summary>
        /// <param name="pRecordList">A pointer to the DNS_RECORD structure that contains the list of DNS records to be freed</param>
        /// <param name="FreeType">A specifier of how the record list should be freed</param>
        [DllImport("dnsapi", CharSet = CharSet.Auto, SetLastError = true)]
        public static extern void DnsRecordListFree(IntPtr pRecordList, DNS_FREE_TYPE FreeType);

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/cc982162(v=vs.85).aspx
        /// </summary>
        [Flags]
        public enum DnsQueryOptions
        {
        DNS_QUERY_STANDARD = 0x0,
        DNS_QUERY_ACCEPT_TRUNCATED_RESPONSE = 0x1,
        DNS_QUERY_USE_TCP_ONLY = 0x2,
        DNS_QUERY_NO_RECURSION = 0x4,
        DNS_QUERY_BYPASS_CACHE = 0x8,
        DNS_QUERY_NO_WIRE_QUERY = 0x10,
        DNS_QUERY_NO_LOCAL_NAME = 0x20,
        DNS_QUERY_NO_HOSTS_FILE = 0x40,
        DNS_QUERY_NO_NETBT = 0x80,
        DNS_QUERY_WIRE_ONLY = 0x100,
        DNS_QUERY_RETURN_MESSAGE = 0x200,
        DNS_QUERY_MULTICAST_ONLY = 0x400,
        DNS_QUERY_NO_MULTICAST = 0x800,
        DNS_QUERY_TREAT_AS_FQDN = 0x1000,
        DNS_QUERY_ADDRCONFIG = 0x2000,
        DNS_QUERY_DUAL_ADDR = 0x4000,
        DNS_QUERY_MULTICAST_WAIT = 0x20000,
        DNS_QUERY_MULTICAST_VERIFY = 0x40000,
        DNS_QUERY_DONT_RESET_TTL_VALUES = 0x100000,
        DNS_QUERY_DISABLE_IDN_ENCODING = 0x200000,
        DNS_QUERY_APPEND_MULTILABEL = 0x800000,
        DNS_QUERY_RESERVED = unchecked((int)0xF0000000)
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/cc982162(v=vs.85).aspx
        /// Also see http://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml
        /// </summary>
        public enum DnsRecordTypes
        {
        DNS_TYPE_A = 0x1,
        DNS_TYPE_NS = 0x2,
        DNS_TYPE_MD = 0x3,
        DNS_TYPE_MF = 0x4,
        DNS_TYPE_CNAME = 0x5,
        DNS_TYPE_SOA = 0x6,
        DNS_TYPE_MB = 0x7,
        DNS_TYPE_MG = 0x8,
        DNS_TYPE_MR = 0x9,
        DNS_TYPE_NULL = 0xA,
        DNS_TYPE_WKS = 0xB,
        DNS_TYPE_PTR = 0xC,
        DNS_TYPE_HINFO = 0xD,
        DNS_TYPE_MINFO = 0xE,
        DNS_TYPE_MX = 0xF,
        DNS_TYPE_TEXT = 0x10,       // This is how it's specified on MSDN
        DNS_TYPE_TXT = DNS_TYPE_TEXT,
        DNS_TYPE_RP = 0x11,
        DNS_TYPE_AFSDB = 0x12,
        DNS_TYPE_X25 = 0x13,
        DNS_TYPE_ISDN = 0x14,
        DNS_TYPE_RT = 0x15,
        DNS_TYPE_NSAP = 0x16,
        DNS_TYPE_NSAPPTR = 0x17,
        DNS_TYPE_SIG = 0x18,
        DNS_TYPE_KEY = 0x19,
        DNS_TYPE_PX = 0x1A,
        DNS_TYPE_GPOS = 0x1B,
        DNS_TYPE_AAAA = 0x1C,
        DNS_TYPE_LOC = 0x1D,
        DNS_TYPE_NXT = 0x1E,
        DNS_TYPE_EID = 0x1F,
        DNS_TYPE_NIMLOC = 0x20,
        DNS_TYPE_SRV = 0x21,
        DNS_TYPE_ATMA = 0x22,
        DNS_TYPE_NAPTR = 0x23,
        DNS_TYPE_KX = 0x24,
        DNS_TYPE_CERT = 0x25,
        DNS_TYPE_A6 = 0x26,
        DNS_TYPE_DNAME = 0x27,
        DNS_TYPE_SINK = 0x28,
        DNS_TYPE_OPT = 0x29,
        DNS_TYPE_DS = 0x2B,
        DNS_TYPE_RRSIG = 0x2E,
        DNS_TYPE_NSEC = 0x2F,
        DNS_TYPE_DNSKEY = 0x30,
        DNS_TYPE_DHCID = 0x31,
        DNS_TYPE_UINFO = 0x64,
        DNS_TYPE_UID = 0x65,
        DNS_TYPE_GID = 0x66,
        DNS_TYPE_UNSPEC = 0x67,
        DNS_TYPE_ADDRS = 0xF8,
        DNS_TYPE_TKEY = 0xF9,
        DNS_TYPE_TSIG = 0xFA,
        DNS_TYPE_IXFR = 0xFB,
        DNS_TYPE_AFXR = 0xFC,
        DNS_TYPE_MAILB = 0xFD,
        DNS_TYPE_MAILA = 0xFE,
        DNS_TYPE_ALL = 0xFF,
        DNS_TYPE_ANY = 0xFF,
        DNS_TYPE_WINS = 0xFF01,
        DNS_TYPE_WINSR = 0xFF02,
        DNS_TYPE_NBSTAT = DNS_TYPE_WINSR
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682056(v=vs.85).aspx
        /// </summary>
        public enum DNS_FREE_TYPE
        {
        DnsFreeFlat = 0,
        DnsFreeRecordList = 1,
        DnsFreeParsedMessageFields = 2
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682082(v=vs.85).aspx
        /// These field offsets could be different depending on endianness and bitness
        /// </summary>
        [StructLayout(LayoutKind.Explicit)]
        public struct DNS_RECORD
        {
        [FieldOffset(0)]
        public IntPtr pNext;    // DNS_RECORD*
        [FieldOffset(4)]
        public IntPtr pName;    // string
        [FieldOffset(8)]
        public ushort wType;
        [FieldOffset(10)]
        public ushort wDataLength;
        [FieldOffset(12)]
        public FlagsUnion Flags;
        [FieldOffset(16)]
        public uint dwTtl;
        [FieldOffset(20)]
        public uint dwReserved;
        [FieldOffset(24)]
        public DataUnion Data;
        }

        [StructLayout(LayoutKind.Explicit)]
        public struct FlagsUnion
        {
        [FieldOffset(0)]
        public uint DW;
        [FieldOffset(0)]
        public DNS_RECORD_FLAGS S;
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682084(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_RECORD_FLAGS
        {
        internal uint data;

        // DWORD Section :2;
        public uint Section
        {
            get { return data & 0x3u; }
            set { data = (data & ~0x3u) | (value & 0x3u); }
        }

        // DWORD Delete :1;
        public uint Delete
        {
            get { return (data >> 2) & 0x1u; }
            set { data = (data & ~(0x1u << 2)) | (value & 0x1u) << 2; }
        }

        // DWORD CharSet :2;
        public uint CharSet
        {
            get { return (data >> 3) & 0x3u; }
            set { data = (data & ~(0x3u << 3)) | (value & 0x3u) << 3; }
        }

        // DWORD Unused :3;
        public uint Unused
        {
            get { return (data >> 5) & 0x7u; }
            set { data = (data & ~(0x7u << 5)) | (value & 0x7u) << 5; }
        }

        // DWORD Reserved :24;
        public uint Reserved
        {
            get { return (data >> 8) & 0xFFFFFFu; }
            set { data = (data & ~(0xFFFFFFu << 8)) | (value & 0xFFFFFFu) << 8; }
        }
        }

        [StructLayout(LayoutKind.Explicit)]
        public struct DataUnion
        {
        [FieldOffset(0)]
        public DNS_A_DATA A;
        [FieldOffset(0)]
        public DNS_SOA_DATA SOA, Soa;
        [FieldOffset(0)]
        public DNS_PTR_DATA PTR, Ptr, NS, Ns, CNAME, Cname, DNAME, Dname, MB, Mb, MD, Md, MF, Mf, MG, Mg, MR, Mr;
        [FieldOffset(0)]
        public DNS_MINFO_DATA MINFO, Minfo, RP, Rp;
        [FieldOffset(0)]
        public DNS_MX_DATA MX, Mx, AFSDB, Afsdb, RT, Rt;
        [FieldOffset(0)]
        public DNS_TXT_DATA HINFO, Hinfo, ISDN, Isdn, TXT, Txt, X25;
        [FieldOffset(0)]
        public DNS_NULL_DATA Null;
        [FieldOffset(0)]
        public DNS_WKS_DATA WKS, Wks;
        [FieldOffset(0)]
        public DNS_AAAA_DATA AAAA;
        [FieldOffset(0)]
        public DNS_KEY_DATA KEY, Key;
        [FieldOffset(0)]
        public DNS_SIG_DATA SIG, Sig;
        [FieldOffset(0)]
        public DNS_ATMA_DATA ATMA, Atma;
        [FieldOffset(0)]
        public DNS_NXT_DATA NXT, Nxt;
        [FieldOffset(0)]
        public DNS_SRV_DATA SRV, Srv;
        [FieldOffset(0)]
        public DNS_NAPTR_DATA NAPTR, Naptr;
        [FieldOffset(0)]
        public DNS_OPT_DATA OPT, Opt;
        [FieldOffset(0)]
        public DNS_DS_DATA DS, Ds;
        [FieldOffset(0)]
        public DNS_RRSIG_DATA RRSIG, Rrsig;
        [FieldOffset(0)]
        public DNS_NSEC_DATA NSEC, Nsec;
        [FieldOffset(0)]
        public DNS_DNSKEY_DATA DNSKEY, Dnskey;
        [FieldOffset(0)]
        public DNS_TKEY_DATA TKEY, Tkey;
        [FieldOffset(0)]
        public DNS_TSIG_DATA TSIG, Tsig;
        [FieldOffset(0)]
        public DNS_WINS_DATA WINS, Wins;
        [FieldOffset(0)]
        public DNS_WINSR_DATA WINSR, WinsR, NBSTAT, Nbstat;
        [FieldOffset(0)]
        public DNS_DHCID_DATA DHCID;
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682044(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_A_DATA
        {
        public uint IpAddress;      // IP4_ADDRESS IpAddress;
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682096(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_SOA_DATA
        {
        public IntPtr pNamePrimaryServer;       // string
        public IntPtr pNameAdministrator;       // string
        public uint dwSerialNo;
        public uint dwRefresh;
        public uint dwRetry;
        public uint dwExpire;
        public uint dwDefaultTtl;
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682080(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_PTR_DATA
        {
        public IntPtr pNameHost;    // string
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682067(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_MINFO_DATA
        {
        public IntPtr pNameMailbox;     // string
        public IntPtr pNameErrorsMailbox;       // string
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682070(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_MX_DATA
        {
        public IntPtr pNameExchange;        // string
        public ushort wPreference;
        public ushort Pad;
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682109(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_TXT_DATA
        {
        public uint dwStringCount;
        public IntPtr pStringArray;     // PWSTR pStringArray[1];
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682074(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_NULL_DATA
        {
        public uint dwByteCount;
        public IntPtr Data;           // BYTE  Data[1];
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682120(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_WKS_DATA
        {
        public uint IpAddress;      // IP4_ADDRESS IpAddress;
        public byte chProtocol;     // UCHAR       chProtocol;
        public IntPtr BitMask;        // BYTE    BitMask[1];
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682035(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_AAAA_DATA
        {
        // IP6_ADDRESS Ip6Address;
        // DWORD IP6Dword[4];
        // This isn't ideal, but it should work without using the fixed and unsafe keywords
        public uint Ip6Address0;
        public uint Ip6Address1;
        public uint Ip6Address2;
        public uint Ip6Address3;
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682061(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_KEY_DATA
        {
        public ushort wFlags;
        public byte chProtocol;
        public byte chAlgorithm;
        public IntPtr Key;        // BYTE Key[1];
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682094(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_SIG_DATA
        {
        public IntPtr pNameSigner;      // string
        public ushort wTypeCovered;
        public byte chAlgorithm;
        public byte chLabelCount;
        public uint dwOriginalTtl;
        public uint dwExpiration;
        public uint dwTimeSigned;
        public ushort wKeyTag;
        public ushort Pad;
        public IntPtr Signature;      // BYTE  Signature[1];
        }

        public const int DNS_ATMA_MAX_ADDR_LENGTH = 20;
        public const int DNS_ATMA_FORMAT_E164 = 1;
        public const int DNS_ATMA_FORMAT_AESA = 2;

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682041(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_ATMA_DATA
        {
        public byte AddressType;
        // BYTE Address[DNS_ATMA_MAX_ADDR_LENGTH];
        // This isn't ideal, but it should work without using the fixed and unsafe keywords
        public byte Address0;
        public byte Address1;
        public byte Address2;
        public byte Address3;
        public byte Address4;
        public byte Address5;
        public byte Address6;
        public byte Address7;
        public byte Address8;
        public byte Address9;
        public byte Address10;
        public byte Address11;
        public byte Address12;
        public byte Address13;
        public byte Address14;
        public byte Address15;
        public byte Address16;
        public byte Address17;
        public byte Address18;
        public byte Address19;
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682076(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_NXT_DATA
        {
        public IntPtr pNameNext;    // string
        public ushort wNumTypes;
        public IntPtr wTypes;       // WORD  wTypes[1];
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682097(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_SRV_DATA
        {
        public IntPtr pNameTarget;      // string
        public ushort uPriority;
        public ushort wWeight;
        public ushort wPort;
        public ushort Pad;
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/cc982164(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_NAPTR_DATA
        {
        public ushort wOrder;
        public ushort wPreference;
        public IntPtr pFlags;       // string
        public IntPtr pService;     // string
        public IntPtr pRegularExpression;       // string
        public IntPtr pReplacement;     // string
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/dd392298(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_OPT_DATA
        {
        public ushort wDataLength;
        public ushort wPad;
        public IntPtr Data;           // BYTE Data[1];
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/dd392296(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_DS_DATA
        {
        public ushort wKeyTag;
        public byte chAlgorithm;
        public byte chDigestType;
        public ushort wDigestLength;
        public ushort wPad;
        public IntPtr Digest;         // BYTE Digest[1];
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/dd392301(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_RRSIG_DATA
        {
        public IntPtr pNameSigner;      // string
        public ushort wTypeCovered;
        public byte chAlgorithm;
        public byte chLabelCount;
        public uint dwOriginalTtl;
        public uint dwExpiration;
        public uint dwTimeSigned;
        public ushort wKeyTag;
        public ushort Pad;
        public IntPtr Signature;      // BYTE  Signature[1];
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/dd392297(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_NSEC_DATA
        {
        public IntPtr pNextDomainName;    // string
        public ushort wTypeBitMapsLength;
        public ushort wPad;
        public IntPtr TypeBitMaps;    // BYTE  TypeBitMaps[1];
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/dd392295(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_DNSKEY_DATA
        {
        public ushort wFlags;
        public byte chProtocol;
        public byte chAlgorithm;
        public ushort wKeyLength;
        public ushort wPad;
        public IntPtr Key;        // BYTE Key[1];
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682104(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_TKEY_DATA
        {
        public IntPtr pNameAlgorithm;   // string
        public IntPtr pAlgorithmPacket; // PBYTE (which is BYTE*)
        public IntPtr pKey;         // PBYTE (which is BYTE*)
        public IntPtr pOtherData;       // PBYTE (which is BYTE*)
        public uint dwCreateTime;
        public uint dwExpireTime;
        public ushort wMode;
        public ushort wError;
        public ushort wKeyLength;
        public ushort wOtherLength;
        public byte cAlgNameLength;     // UCHAR cAlgNameLength;
        public int bPacketPointers;     // BOOL  bPacketPointers;
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682106(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_TSIG_DATA
        {
        public IntPtr pNameAlgorithm;   // string
        public IntPtr pAlgorithmPacket; // PBYTE (which is BYTE*)
        public IntPtr pSignature;       // PBYTE (which is BYTE*)
        public IntPtr pOtherData;       // PBYTE (which is BYTE*)
        public long i64CreateTime;
        public ushort wFudgeTime;
        public ushort wOriginalXid;
        public ushort wError;
        public ushort wSigLength;
        public ushort wOtherLength;
        public byte cAlgNameLength;     // UCHAR    cAlgNameLength;
        public int bPacketPointers;     // BOOL     bPacketPointers;
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682114(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_WINS_DATA
        {
        public uint dwMappingFlag;
        public uint dwLookupTimeout;
        public uint dwCacheTimeout;
        public uint cWinsServerCount;
        public uint WinsServers;    // IP4_ADDRESS WinsServers[1];
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682113(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_WINSR_DATA
        {
        public uint dwMappingFlag;
        public uint dwLookupTimeout;
        public uint dwCacheTimeout;
        public IntPtr pNameResultDomain;    // string
        }

        /// <summary>
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/dd392294(v=vs.85).aspx
        /// </summary>
        [StructLayout(LayoutKind.Sequential)]
        public struct DNS_DHCID_DATA
        {
        public uint dwByteCount;
        public IntPtr DHCID;          // BYTE  DHCID[1];
        }

        /// <summary>
        /// Converts an unsigned int to an ip address object
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/cc982163(v=vs.85).aspx
        /// </summary>
        /// <param name="ipAddress">The unsigned int to convert to an ip address object</param>
        /// <returns>The converted ip address</returns>
        public static IPAddress ConvertUintToIpAddress(uint ipAddress)
        {
        // x86 is in little endian
        // Network byte order (what the IPAddress object requires) is big endian
        // Ex - 0x7F000001 is 127.0.0.1
        var addressBytes = new byte[4];
        addressBytes[0] = (byte)((ipAddress & 0xFF000000u) >> 24);
        addressBytes[1] = (byte)((ipAddress & 0x00FF0000u) >> 16);
        addressBytes[2] = (byte)((ipAddress & 0x0000FF00u) >> 8);
        addressBytes[3] = (byte)(ipAddress & 0x000000FFu);
        return new IPAddress(addressBytes);
        }

        /// <summary>
        /// Converts the data from the AAAA record into an ip address object
        /// See http://msdn.microsoft.com/en-us/library/windows/desktop/ms682140(v=vs.85).aspx
        /// </summary>
        /// <param name="data">The AAAA record to convert</param>
        /// <returns>The converted ip address</returns>
        public static IPAddress ConvertAAAAToIpAddress(DNS_AAAA_DATA data)
        {
        var addressBytes = new byte[16];
        addressBytes[0] = (byte)(data.Ip6Address0 & 0x000000FF);
        addressBytes[1] = (byte)((data.Ip6Address0 & 0x0000FF00) >> 8);
        addressBytes[2] = (byte)((data.Ip6Address0 & 0x00FF0000) >> 16);
        addressBytes[3] = (byte)((data.Ip6Address0 & 0xFF000000) >> 24);
        addressBytes[4] = (byte)(data.Ip6Address1 & 0x000000FF);
        addressBytes[5] = (byte)((data.Ip6Address1 & 0x0000FF00) >> 8);
        addressBytes[6] = (byte)((data.Ip6Address1 & 0x00FF0000) >> 16);
        addressBytes[7] = (byte)((data.Ip6Address1 & 0xFF000000) >> 24);
        addressBytes[8] = (byte)(data.Ip6Address2 & 0x000000FF);
        addressBytes[9] = (byte)((data.Ip6Address2 & 0x0000FF00) >> 8);
        addressBytes[10] = (byte)((data.Ip6Address2 & 0x00FF0000) >> 16);
        addressBytes[11] = (byte)((data.Ip6Address2 & 0xFF000000) >> 24);
        addressBytes[12] = (byte)(data.Ip6Address3 & 0x000000FF);
        addressBytes[13] = (byte)((data.Ip6Address3 & 0x0000FF00) >> 8);
        addressBytes[14] = (byte)((data.Ip6Address3 & 0x00FF0000) >> 16);
        addressBytes[15] = (byte)((data.Ip6Address3 & 0xFF000000) >> 24);

        return new IPAddress(addressBytes);
        }
    }
    }

Alternative Managed API:

System.Net.Dns.GetHostEntry(Name)