C# Signature:

[DllImport("iphlpapi.dll", CharSet=CharSet.Ansi)]
public static extern int GetAdaptersInfo(IntPtr pAdapterInfo, ref Int64 pBufOutLen);

VB Signature:

<DllImport("iphlpapi.dll", EntryPoint:="GetAdaptersInfo", CharSet:=CharSet.Ansi)> _
Private Shared Function GetAdaptersInfo( _
     ByVal pAdapterInfo As IntPtr, _
     ByRef pBufOutLen As UInt64) As Int32
End Function

Tip

In .NET 2.0, this library (The IP Helper API) is encapsulated in the NetworkInformation class.

Sample Code:

Public Sub GetAdapters()
     Dim structSize As Int32 = Marshal.SizeOf(GetType(IP_ADAPTER_INFO))
     Dim pArray As IntPtr = Marshal.AllocHGlobal(structSize)

     Dim len As UInt64 = Convert.ToUInt64(structSize)
     Dim ret As Int32 = GetAdaptersInfo(pArray, len)

     If ret = 111 Then
     ' Buffer was too small, reallocate the correct size for the buffer.
     pArray = Marshal.ReAllocHGlobal(pArray, New IntPtr(Convert.ToInt64(len)))
     ret = GetAdaptersInfo(pArray, len)
     End If

     If ret = 0 Then
     ' Call succeeded
     Dim pEntry As IntPtr = pArray
     Do
        ' Retrieve the adapter info from the memory address.
         Dim Entry As IP_ADAPTER_INFO = CType(Marshal.PtrToStructure(pEntry, GetType(IP_ADAPTER_INFO)), IP_ADAPTER_INFO)
         pEntry = Entry.Next
     Loop Until IntPtr.op_Equality(pEntry, IntPtr.Zero)
     End If

     Marshal.FreeHGlobal(pArray)
End Sub

Notes:

GetAdaptersInfo returns a pointer to an IP_ADAPTER_INFO linked list.