BUG: Numeric Hostnames Used in Winsock Control Resolve Improperly

ID: Q244823

The information in this article applies to:

Microsoft Visual Basic Enterprise Edition for Windows, versions 5.0, 6.0

SYMPTOMS

If a computer has a hostname that is all numerals, or if the local computer name is all numerals, the Winsock Control will not function properly in two cases:

If you attempt to connect to a hostname that is all numerals, the name will not be resolved to a real IP Address, therefore the connection will never be made.

If the local computer's hostname is all numerals, the LocalIP property returns what appears to be an invalid IP Address.

If the local computer name is a numeric name, the Winsock Control LocalIP property returns an incorrect IP address. It will actually return the numeric named in dotted notation versus doing a real-name lookup on the name.

For example, if a computer name is named "1234567" then LocalIP returns 0.18.214.135. This potentially breaks applications when you use the bind method on the LocalIP property in certain situations.

The reason for having a computer name of all numerals is for large installations that use it as a serial number. This is not a problem on Windows 2000 since it does not allow numeric computer names, however it would present a problem if trying to connect to a host with a numeric name.

CAUSE

The Winsock Control tries to intelligently resolve names by using the inet_ntoa() Winsock API call to first try converting the name into an IP Address. If that succeeds, normal name resolution through gethostbyname() is bypassed.

The Winsock API inet_ntoa() call given a value returns the dotted notation of the value. Therefore, a numeric hostname or local computer name will not get resolved to its true IP Address, but rather a dotted representation of the numeric name. So for example, if a computer is named "1234567", inet_ntoa() returns 0.18.214.135.

RESOLUTION

The only resolution is to use non-numeric hostnames or computer names with the Winsock Control, or use the Winsock API to resolve the names through the Winsock API SDK calls gethostname()/gethostbyname().

For additional information on using these calls in Visual Basic, click the article numbers below to view the articles in the Microsoft Knowledge Base:

Q160215 HOWTO: Obtain the Host IP Address Using Windows Sockets

Q154512 SAMPLE: Getting HostAddress Using Windows Sockets

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

Some customer installations name the computers according to an asset tag or serial number that is all numerals. It is in these cases the problem manifests itself.

Steps to Reproduce Behavior

Using the Network Identification tab of the Network Control Panel, set the computer name to all numerals (for example, "1234567")

Using Visual Basic, create a new project.

Add the Winsock Control as a component and place on the main form.

Add the following to the form's code module:

Option Explicit

Private Sub Form_Load()
  MsgBox Winsock1.LocalIP
End Sub

Run the program and you will notice the program displays the wrong Local IP Address

REFERENCES

For more information, please refer to:

Microsoft Visual Basic Documentation for the Winsock Control

Platform SDK: Windows Sockets Version 2

Additional query words:

Keywords : kbnetwork kbAPI kbCtrl kbSDKPlatform kbSDKWin32 kbVBp500 kbVBp600 kbDSupport kbGrpNet
Version : WINDOWS:5.0,6.0
Platform : WINDOWS
Issue type : kbbug