Visual Basic Network Services

Netbios: Determine Local Adapter MAC Address
Posted:   Friday August 21, 1998
Updated:   Monday December 26, 2011
Applies to:   VB4-32, VB5, VB6
Developed with:   VB6, Windows NT4
OS restrictions:   None
Author:   VBnet - Randy Birch, MSKB  
Related:   Netbios: Determine Local Adapter MAC Address
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Installed network card, NetBIOS.

Keeping it simple, this is a wrapper routine that will return the Medium Access Control (MAC) address for the installed network card. A MAC Address is a unique 48-bit number assigned to the network interface card (NIC) by the manufacturer. MAC addresses (which are physical addresses) are used for mapping in TCP/IP network communication.

TCP\IP under Windows NT allows a computer to communicate over a network with another computer by using either an IP address, a host name, or a NetBIOS name. However, when one computer attempts to communicate with another computer using one of these three naming conventions, that name must ultimately be resolved to a hardware address, the MAC address.

This code is roughly based on MS knowledge base article Q175472.

 BAS Module Code

 Form Code
To a form add a command button (Command1), and a text box (Text1). Labels and frames are optional. Add the following:

Option Explicit
' Copyright 1996-2011 VBnet/Randy Birch, All Rights Reserved.
' Some pages may also contain other copyrights by the author.
' Distribution: You can freely use this code in your own
'               applications, but you may not reproduce 
'               or publish this code on any web site,
'               online service, or distribute as source 
'               on any media without express permission.
Private Const NCBASTAT As Long = &H33
Private Const NCBNAMSZ As Long = 16
Private Const HEAP_ZERO_MEMORY As Long = &H8
Private Const NCBRESET As Long = &H32

   ncb_command    As Byte
   ncb_retcode    As Byte
   ncb_lsn        As Byte
   ncb_num        As Byte
   ncb_buffer     As Long
   ncb_length     As Integer
   ncb_callname   As String * NCBNAMSZ
   ncb_name       As String * NCBNAMSZ
   ncb_rto        As Byte
   ncb_sto        As Byte
   ncb_post       As Long
   ncb_lana_num   As Byte
   ncb_cmd_cplt   As Byte
   ncb_reserve(9) As Byte 'Reserved, must be 0
   ncb_event      As Long
End Type

   adapter_address(5) As Byte
   rev_major         As Byte
   reserved0         As Byte
   adapter_type      As Byte
   rev_minor         As Byte
   duration          As Integer
   frmr_recv         As Integer
   frmr_xmit         As Integer
   iframe_recv_err   As Integer
   xmit_aborts       As Integer
   xmit_success      As Long
   recv_success      As Long
   iframe_xmit_err   As Integer
   recv_buff_unavail As Integer
   t1_timeouts       As Integer
   ti_timeouts       As Integer
   Reserved1         As Long
   free_ncbs         As Integer
   max_cfg_ncbs      As Integer
   max_ncbs          As Integer
   xmit_buf_unavail  As Integer
   max_dgram_size    As Integer
   pending_sess      As Integer
   max_cfg_sess      As Integer
   max_sess          As Integer
   max_sess_pkt_size As Integer
   name_count        As Integer
End Type
Private Type NAME_BUFFER
   name        As String * NCBNAMSZ
   name_num    As Integer
   name_flags  As Integer
End Type

Private Type ASTAT
   adapt          As ADAPTER_STATUS
   NameBuff(30)   As NAME_BUFFER
End Type

Private Declare Function Netbios Lib "netapi32" _
   (pncb As NET_CONTROL_BLOCK) As Byte
Private Declare Sub CopyMemory Lib "kernel32" _
   Alias "RtlMoveMemory" _
  (hpvDest As Any, ByVal _
   hpvSource As Long, ByVal _
   cbCopy As Long)
Private Declare Function GetProcessHeap Lib "kernel32" () As Long

Private Declare Function HeapAlloc Lib "kernel32" _
  (ByVal hHeap As Long, _
   ByVal dwFlags As Long, _
   ByVal dwBytes As Long) As Long
Private Declare Function HeapFree Lib "kernel32" _
  (ByVal hHeap As Long, _
   ByVal dwFlags As Long, _
   lpMem As Any) As Long

Private Sub Command1_Click()

  'in calling, pass the character you
  'want as a delimiter between MAC
  'address members
   Text1.Text = GetMACAddress("-")
End Sub

Private Function GetMACAddress(sDelimiter As String) As String

  'retrieve the MAC Address for the network controller
  'installed, returning a formatted string
   Dim tmp As String
   Dim pASTAT As Long
   Dim cnt As Long

  'The IBM NetBIOS 3.0 specifications defines four basic
  'NetBIOS environments under the NCBRESET command. Win32
  'follows the OS/2 Dynamic Link Routine (DLR) environment.
  'This means that the first NCB issued by an application
  'must be a NCBRESET, with the exception of NCBENUM.
  'The Windows NT implementation differs from the IBM
  'NetBIOS 3.0 specifications in the NCB_CALLNAME field.
   NCB.ncb_command = NCBRESET
   Call Netbios(NCB)
  'To get the Media Access Control (MAC) address for an
  'ethernet adapter programmatically, use the Netbios()
  'NCBASTAT command and provide a "*" as the name in the
  'NCB.ncb_CallName field (in a 16-chr string).
   NCB.ncb_callname = "*               "
   NCB.ncb_command = NCBASTAT
  'For machines with multiple network adapters you need to
  'enumerate the LANA numbers and perform the NCBASTAT
  'command on each. Even when you have a single network
  'adapter, it is a good idea to enumerate valid LANA numbers
  'first and perform the NCBASTAT on one of the valid LANA
  'numbers. It is considered bad programming to hardcode the
  'LANA number to 0 (see the comments section below).
   NCB.ncb_lana_num = 0
   NCB.ncb_length = Len(AST)
   pASTAT = HeapAlloc(GetProcessHeap(), _
                      HEAP_GENERATE_EXCEPTIONS Or _
                      HEAP_ZERO_MEMORY, _
   If pASTAT <> 0 Then
      NCB.ncb_buffer = pASTAT
      Call Netbios(NCB)
      CopyMemory AST, NCB.ncb_buffer, Len(AST)
     'convert the byte array to a string     
      GetMACAddress = MakeMacAddress(AST.adapt.adapter_address(), sDelimiter)
      HeapFree GetProcessHeap(), 0, pASTAT

      Debug.Print "memory allocation failed!"
      Exit Function
   End If
End Function

Private Function MakeMacAddress(b() As Byte, sDelim As String) As String

   Dim cnt As Long
   Dim buff As String
   On Local Error GoTo MakeMac_error
  'so far, MAC addresses are
  'exactly 6 segments in size (0-5)
   If UBound(b) = 5 Then
     'concatenate the first five values
     'together and separate with the
     'delimiter char
      For cnt = 0 To 4
         buff = buff & Right$("00" & Hex(b(cnt)), 2) & sDelim
     'and append the last value
      buff = buff & Right$("00" & Hex(b(5)), 2)
   End If  'UBound(b)
   MakeMacAddress = buff
   Exit Function
   MakeMacAddress = "(error building MAC address)"
   Resume MakeMac_exit
End Function
Other hardware and software may be assigned their own MAC addresses. For example, a modem can have a MAC address. Also, a RAS client or server can install "dummy" network adapters that correspond to a dialup or serial connection. Normally, these MAC addresses are randomly generated. If an adapter status is called on a LANA that corresponds to one of these adapters when no connection is present, NetBIOS returns error 0x34 (NRC_ENVNOTDEF) even if a reset was previously performed.

With the NetBEUI and IPX transports, the same information can be obtained at a command prompt by using:

     net config workstation

The ID given is the MAC address.

How to Use LANA Numbers in a 32-bit Environment
Last reviewed: August 7, 1996
Article ID: Q138037
The information in this article applies to:
Microsoft Win32 Software Development Kit (SDK) versions 3.1, 3.5, 3.51, 4.0

NetBIOS uses the concept of a LANA (LAN adapter number) that allows you to write transport-independent NetBIOS applications. This article describes what a LANA is and recommends an approach to writing NetBIOS applications.

A LANA is a field of the NetBIOS NCB structure. In IBM's NetBIOS 3.0 specification, a LANA was used to specify a particular network adapter, as NetBIOS then supported up to two network adapters in one PC computer. Specifying a LANA of zero directed a request to the first adapter, and specifying a LANA of one directed a request to the second adapter.

Originally, IBM sent NetBIOS packets over the NetBEUI protocol, also known as the NetBIOS Frames protocol. This was the only transport NetBIOS could use to send data across the network. In other words, each network adapter had only one protocol to send and receive NetBIOS packets.

Because most computers have only one network adapter, many MS-DOS-based applications send all their requests to a LANA value of zero (also called simply 'LANA zero'). If a second network adapter is installed, some programs allow the user to configure the application to use LANA one instead. As a result, LANA zero became a default setting, though it was never intended to be a default.

Today's network technology allows NetBIOS to use transports other than NetBEUI. Microsoft has extended the meaning of LANA to indicate a specific transport on a specific adapter. For example, if you have two network adapters, and have IPX/SPX and NetBEUI transports installed, you have four LANAs. The LANAs may or may not be sequential, and there is no systematic way to identify which transport maps to which LANA.

In addition to extending the meaning of a LANA, Microsoft also added an NCB command (NCBENUM) that returns an array of available LANA numbers. As an example, the LANA_ENUM structure filled by NCBENUM might hold an array with values 0, 3, 5, and 6. Zero might map to IPX/SPX on the first adapter, three might map to NETBEUI on a second adapter, and so on.

In Windows NT and Windows 95, network adapters consist of physical adapters (like a 3Com Etherlink II) and software adapters (like the Dial Up Adapter). In addition, a user may have TCP/IP, NETBEUI, IPX/SPX, and other transports installed, all of which have NetBIOS support.

For Windows NT, LANAs are configurable through the control panel. Choose the Network applet, choose the NetBIOS Interface component, then choose Configure. A dialog appears that allows you to edit the LANAs.

For Windows 95, you may only set LANA zero, the default protocol, and if no protocol is set as default, there won't be a LANA zero. You can set the default protocol in the control panel. Choose the Network applet, choose the protocol you want as default, choose Properties, the Advanced tab, and finally check 'Set this protocol to be the default protocol'.

LANAs may seem like a constraint that your application must work around. However, making your application ignorant of how users want to configure their machines is a powerful idea, and one that makes life easier for your customers.

The best way to write a NetBIOS application is to support all LANAs, and establish connections over any LANA. A good approach is outlined in the following steps:

  • Enumerate the LANAs by submitting NCBENUM.
  • Reset each LANA by submitting one NCBRESET per LANA.
  • Add your local NetBIOS name to each LANA. The name may be the same on each LANA.
  • Connect using any LANA:
  • For servers, submit an NCBLISTEN on each LANA. If necessary, cancel any outstanding listen after the first listen is satisfied.
  • For clients, submit an NCBFINDNAME (Windows NT only) or an NCBCALL (either Windows NT or Windows 95) on each LANA. The first successful find name or call will indicate which LANA to use. When using NCBCALL instead of NCBFINDNAME, you must cancel any pending NCBCALLs and hang up the extra completed calls (when two or more calls are successful.)

It is a good idea to submit NCBADDNAME, NCBLISTEN, NCBFINDNAME, and NCBCALL asynchronously. Asynchronous requests will be processed almost in parallel on each transport.

This architecture is quite beneficial. Once your application is written to establish connections in this manner, it will support any transport that NetBIOS can use. As a result, your customers will not have to configure anything within your application, and your application will not be affected by dynamic LANAs such as dial-up adapters or plug-and-play hardware.

Last reviewed: August 7, 1996
1998 Microsoft Corporation. All rights reserved.


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