HOWTO: Get the MAC Address for an Ethernet Adapter

• Microsoft Win32 Software Development Kit (SDK) on the following platforms:

      - Microsoft Windows NT versions 3.1, 3.5, 3.51
      - Microsoft Windows 95
  

SUMMARY

This article demonstrates how to get the Media Access Control (MAC) address for an ethernet adapter programmatically by using NetBIOS, if your card is bound to NetBIOS.

MORE INFORMATION

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. This is demonstrated in the sample code below.

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.

In addition, 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 following code enumerates all LANA numbers, performs a reset (NCBREST), and an adapter status (NCBASTAT).

Sample Code

   #include <windows.h>
   #include <wincon.h>
   #include <stdlib.h>
   #include <stdio.h>
   #include <time.h>

   typedef struct _ASTAT_
   {
      ADAPTER_STATUS adapt;
      NAME_BUFFER    NameBuff [30];
   }ASTAT, * PASTAT;

   ASTAT Adapter;

   void main (void)
   {
      NCB Ncb;
      UCHAR uRetCode;
      char NetName[50];
      LANA_ENUM   lenum;
      int      i;

      memset( &Ncb, 0, sizeof(Ncb) );
      Ncb.ncb_command = NCBENUM;
      Ncb.ncb_buffer = (UCHAR *)&lenum;
      Ncb.ncb_length = sizeof(lenum);
      uRetCode = Netbios( &Ncb );
      printf( "The NCBENUM return code is: 0x%x \n", uRetCode );

      for(i=0; i < lenum.length ;i++)
      {
          memset( &Ncb, 0, sizeof(Ncb) );
          Ncb.ncb_command = NCBRESET;
          Ncb.ncb_lana_num = lenum.lana[i];

          uRetCode = Netbios( &Ncb );
          printf( "The NCBRESET on LANA %d return code is: 0x%x \n",
                  lenum.lana[i], uRetCode );

          memset( &Ncb, 0, sizeof (Ncb) );
          Ncb.ncb_command = NCBASTAT;
          Ncb.ncb_lana_num = lenum.lana[i];

          strcpy( Ncb.ncb_callname,  "*               " );
          Ncb.ncb_buffer = (char *) &Adapter;
          Ncb.ncb_length = sizeof(Adapter);

          uRetCode = Netbios( &Ncb );
          printf( "The NCBASTAT on LANA %d return code is: 0x%x \n",
                  lenum.lana[i], uRetCode );
          if ( uRetCode == 0 )
          {
             printf( "The Ethernet Number on LANA %d is:
                     %02x%02x%02x%02x%02x%02x\n",
            lenum.lana[i],
                  Adapter.adapt.adapter_address[0],
                  Adapter.adapt.adapter_address[1],
                  Adapter.adapt.adapter_address[2],
                  Adapter.adapt.adapter_address[3],
                  Adapter.adapt.adapter_address[4],
                  Adapter.adapt.adapter_address[5] );
          }
       }
   }

Keywords          : NtwkNetBios
Version           : WINNT:3.0,3.5,3.51;WIN95
Platform          : Win95 winnt
Issue type        : kbhowto