C# Signature:

[DllImport("iphlpapi.dll", SetLastError = true)]

public static extern uint GetExtendedUdpTable(IntPtr pTcpTable, ref int dwOutBufLen, bool sort, int ipVersion, UDP_TABLE_CLASS tblClass, uint reserved = 0);

VB Signature:

User-Defined Types:

public enum UDP_TABLE_CLASS

    {
    UDP_TABLE_BASIC,
    UDP_TABLE_OWNER_PID,
    UDP_TABLE_OWNER_MODULE
    }
    [StructLayout(LayoutKind.Sequential)]
    public struct MIB_UDP6ROW_OWNER_PID
    {
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 16)]
    public byte[] localAddr;
    public uint localScopeId;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
    public byte[] localPort;

    public long LocalScopeId
    {
        get { return localScopeId; }
    }

    public IPAddress LocalAddress
    {
        get { return new IPAddress(localAddr, LocalScopeId); }
    }

    public ushort LocalPort
    {
        get { return BitConverter.ToUInt16(localPort.Take(2).Reverse().ToArray(), 0); }
    }
    }
    [StructLayout(LayoutKind.Sequential)]
    public struct MIB_UDP6TABLE_OWNER_PID
    {
    public uint dwNumEntries;
    [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.Struct, SizeConst = 1)]
    public MIB_UDP6ROW_OWNER_PID[] table;
    }
    [StructLayout(LayoutKind.Sequential)]
    public struct MIB_UDPTABLE_OWNER_PID
    {
    public uint dwNumEntries;
    [MarshalAs(UnmanagedType.ByValArray, ArraySubType = UnmanagedType.Struct, SizeConst = 1)]
    public MIB_UDPROW_OWNER_PID[] table;
    }
    [StructLayout(LayoutKind.Sequential)]
    public struct MIB_UDPROW_OWNER_PID
    {
    public uint localAddr;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
    public byte[] localPort;
    public uint owningPid;

    public uint ProcessId
    {
        get { return owningPid; }
    }

    public IPAddress LocalAddress
    {
        get { return new IPAddress(localAddr); }
    }

    public ushort LocalPort
    {
        get
        {
        return BitConverter.ToUInt16(new byte[2] { localPort[1], localPort[0] }, 0);
        }
    }
    }

Alternative Managed API:

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Notes:

public const int AF_INET = 2; // IP_v4 = System.Net.Sockets.AddressFamily.InterNetwork

public const int AF_INET6 = 23; // IP_v6 = System.Net.Sockets.AddressFamily.InterNetworkV6

public static List<MIB_UDPROW_OWNER_PID> GetAllUDPConnections()

    {
        return GetUDPConnections<MIB_UDPROW_OWNER_PID, MIB_UDPTABLE_OWNER_PID>(AF_INET);
    }

private static List<IPR> GetUDPConnections<IPR, IPT>(int ipVersion)//IPR = Row Type, IPT = Table Type

    {
        IPR[] tableRows;
        int buffSize = 0;

        var dwNumEntriesField = typeof(IPT).GetField("dwNumEntries");

        // how much memory do we need?
        uint ret = GetExtendedUdpTable(IntPtr.Zero, ref buffSize, true, ipVersion, UDP_TABLE_CLASS.UDP_TABLE_OWNER_PID);
        IntPtr tcpTablePtr = Marshal.AllocHGlobal(buffSize);

        try
        {
        ret = GetExtendedUdpTable(tcpTablePtr, ref buffSize, true, ipVersion, UDP_TABLE_CLASS.UDP_TABLE_OWNER_PID);
        if (ret != 0)
            return new List<IPR>();

        // get the number of entries in the table
        IPT table = (IPT)Marshal.PtrToStructure(tcpTablePtr, typeof(IPT));
        int rowStructSize = Marshal.SizeOf(typeof(IPR));
        uint numEntries = (uint)dwNumEntriesField.GetValue(table);

        // buffer we will be returning
        tableRows = new IPR[numEntries];

        IntPtr rowPtr = (IntPtr)((long)tcpTablePtr + 4);
        for (int i = 0; i < numEntries; i++)
        {
            IPR tcpRow = (IPR)Marshal.PtrToStructure(rowPtr, typeof(IPR));
            tableRows[i] = tcpRow;
            rowPtr = (IntPtr)((long)rowPtr + rowStructSize);   // next entry
        }
        }
        finally
        {
        // Free the Memory
        Marshal.FreeHGlobal(tcpTablePtr);
        }
        return tableRows != null ? tableRows.ToList() : new List<IPR>();
    }

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