How to Use WinSock to Enumerate Addresses

• Microsoft Win32 Software Development Kit (SDK) for Windows NT versions 3.5 and 3.51

SUMMARY

The gethostbyname() and gethostname() WinSock database APIs can be used to list IP addresses for a multihomed host. However, these functions work only for IP addresses. This article shows by example how to give addresses for other address families. Two different methods are given.

MORE INFORMATION

Method One Code Sample

AF_IPX:

This function can be used to give an IPX address:

   #include <winsock.h>
   #include <wsipx.h>
   #include <wsnwlink.h>

   #include <stdlib.h>

   // Note:  In the interest of clarity, the following code does not check
   //        return values or handle error conditions.

   void IPXEnum()
   {
      int            cAdapters,
                     cbOpt  = sizeof( cAdapters ),
                     cbAddr = sizeof( SOCKADDR_IPX );

      SOCKET         s;
      SOCKADDR_IPX   Addr;

      // Create IPX socket.
      s = socket( AF_IPX, SOCK_DGRAM, NSPROTO_IPX );

      // Socket must be bound prior to calling IPX_MAX_ADAPTER_NUM
      memset( &Addr, 0, sizeof( Addr ));
      Addr.sa_family = AF_IPX;
      bind( s, (SOCKADDR*) &Addr, cbAddr);

      // Get the number of adapters => cAdapters.
      getsockopt( (SOCKET) s, NSPROTO_IPX, IPX_MAX_ADAPTER_NUM,
                  (char *) &cAdapters, &cbOpt );
      // At this point cAdapters is the number of installed adapters.
      while ( cAdapters > 0 )
      {
         IPX_ADDRESS_DATA  IpxData;

         memset( &IpxData, 0, sizeof(IpxData));

         // Specify which adapter to check.
         IpxData.adapternum = cAdapters - 1;
         cbOpt = sizeof( IpxData );

         // Get information for the current adapter.
         getsockopt( s, NSPROTO_IPX, IPX_ADDRESS,
                     (char*) &IpxData, &cbOpt );

         // IpxData contains the address for the current adapter.
         cAdapters--;
      }
   }

This function uses the EnumProtocols() function to give lana numbers for the available NetBIOS transports. NOTE: This doesn't work under Windows NT 3.5 because of a bug in EnumProtocols(), but it does work under Windows NT 3.51.

   void NBEnum()
   {
      DWORD          cb = 0;
      PROTOCOL_INFO *pPI;
      BOOL           pfLanas[100];

      int            iRes,
                     nLanas = sizeof(pfLanas) / sizeof(BOOL);

      // Specify NULL for lpiProtocols to enumerate all protocols.

      // First, determine the output buffer size.
      iRes = EnumProtocols( NULL, NULL, &cb );

      // Verify the expected error was received.
      assert( iRes == -1 && GetLastError() == ERROR_INSUFFICIENT_BUFFER );
      if (!cb)
      {
         fprintf( stderr, "No available NetBIOS transports.\n");
         break;
      }

      // Allocate a buffer of the specified size.
      pPI = (PROTOCOL_INFO*) malloc( cb );

      // Enumerate all protocols.
      iRes = EnumProtocols( NULL, pPI, &cb );

      // EnumProtocols() lists each lana number twice, once for
      // SOCK_DGRAM and once for SOCK_SEQPACKET. Set a flag in pfLanas
      // so unique lanas can be identified.

      memset( pfLanas, 0, sizeof( pfLanas ));

      while (iRes > 0)
         // Scan protocols looking for AF_NETBIOS.
         if ( pPI[--iRes].iAddressFamily == AF_NETBIOS )
            // found one
            pfLanas[ pPI[iRes].iProtocol ] = TRUE;

      fprintf( stderr, "Available NetBIOS lana numbers: " );
      while( nLanas-- )
         if ( pfLanas[nLanas] )
            fprintf( stderr, "%d ", nLanas );

      free( pPI );
   }

Address enumeration is not meaningful for AF_APPLETALK. On a multihomed host with routing disabled, only the default adapter is used. If routing is enabled, a single AppleTalk address is used for all installed network adapters.

Method Two: Code Sample

Listed below is an example of how to use the WinSock database APIs to give IP addresses:

   void EnumIP()
   {
      char     szHostname[100];
      HOSTENT *pHostEnt;
      int      nAdapter = 0;

      gethostname( szHostname, sizeof( szHostname ));
      pHostEnt = gethostbyname( szHostname );

      while ( pHostEnt->h_addr_list[nAdapter] )
      {
         // pHostEnt->h_addr_list[nAdapter] is the current address in host
         //  order.

         nAdapter++;
      }
   }