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Troubleshooting Server Message Block inbound connection limit in Windows peer-to-peer workgroup
Article ID: 328459 - View products that this article applies to.
This article was previously published under Q328459
In a peer-to-peer workgroup, when you try to connect to the network resources of a computer that is running any of the products listed at the beginning of this article, you may receive one of the following error messages:
Operating system error 71.
No more connections can be made to this remote computer at this time because there are already as many connections as the computer can accept.
This problem occurs when a computer reaches the maximum number of host connections that are allowed. In this case, when a NULL session connection is generated in the Microsoft Windows 2000 client, this NULL session connection is counted as one session on the Microsoft Windows XP-based server. Therefore, the error messages occur that are mentioned in this "Symptom" section, even if the number of connections to computers do not exceed the limit.
System error 71 has occurred.
This remote computer has reached its connection limit, you cannot connect at this time.
In addition, when multiple NULL sessions are generated from a single Windows 2000 client computer, the multiple NULL sessions are counted as multiple sessions. However, a NULL session appears as a single session when you run the net session command. In this case, when the RestrictAnonymous registry entry is set, and the NULL session connection is rejected, this symptom still occurs.
A Windows client workstation may have opened a pipe connection to the named pipe \PIPE\spoolss on either a print server or a workstation that has a shared printer. This typically occurs when you start a program (such as Microsoft Word) that queries printers, or if you open the Printers folder in Control Panel. Printer spooling on both the client and the server will open a handle related to this connection.
A Remote Procedure Call (RPC) requires one named pipe instance for every active RPC call (like OpenPrinter). If an OpenPrinter call stops responding, RPC keeps open the named pipe connection. RPC does not disconnect this connection until the context handle (that is OpenPrinters) has been closed.
If both the following conditions are true, you may open an anonymous connection (also known as null session connection) that never closes to the named pipe \PIPE\spoolss on the workstation that acts as the server in your peer to peer network:
Use one of the following methods to restrict null session connections on your workstation that is acting as a print server. The preferred method is the first one.
Method 1Disable null session connections on the Windows computer that exceeds its incoming connection limit and shows some additional null session connections either by using the Group Policy GUI or by setting a registry key.
Using the Group Policy User Interface (Local Security Policy MMC Snap-In)
Using Registry EditorImportant This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/322756/ )How to back up and restore the registry in Windows
To restrict null session connections (or disable null session access):
Method 2Use the following method to avoid null session connections that have a high session idle time and that have opened a handle to the named pipe \PIPE\spoolss.
Remove Printer Share on ClientsIdentify clients that have local printer shares enabled (see the "More Information" section for additional information) and remove all local printer shares on these computers:
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Computers that run Windows NT Workstation 4.0, Windows 2000 Professional, and Windows XP Professional are licensed for a maximum of 10 concurrent client incoming sessions. Computers that run Windows XP Home Edition are licensed for a maximum of 5 concurrent client incoming sessions. All logical drive, logical printer, and transport level connections combined from a single computer are one session.
If the server service already has the maximum number of open sessions and one more user tries to allocate a resource, the computer returns the error messages that are described in the "Symptoms" section of this article.
Typically a computer does not have multiple sessions to another computer. But there are exceptions. For example, computer A is running a service under another user context than the logged-on user, and that service creates a logical connection to computer B. The logical connection can result from file shares, printers, serial ports, and also from communication between computers using named pipes and mail slots.
Use the following commands to get information about sessions and open files and shared resources.
Information About Active Sessions on the Computer That Is Running the Server ServiceTo receive information about active sessions on the computer that is running the server service, type the following command:
net sessionCount the number of open sessions to see if the session limit of 10, or 5 in the case of Windows XP Home Edition, is already reached. Typically there is only one session per remote client.
If there is more than one session from a remote client, view the User name context on the remote client that has set up more than one session:
Temporary null sessions are usually caused by IPC$ connections as the first step in establishing a connection. They stay active for 30 seconds to 90 seconds.
Note To disconnect client computer sessions, use the following command:
net session /delete \\computernameThis command disconnects all sessions from that computer and closes all open files. This command may cause data loss if open files that have not been saved are closed.
Information About Open FilesTo receive information about open files, on the computer that is running the server service, type the following command:
net filesIf you have seen permanent null user sessions in the session table, determine which file or pipe the null user is using.
Information About NetBIOS Connection TableTo see a listing of incoming and outgoing connections and the amount of traffic carried on these connections, type the command:
Information About Shared ResourcesTo see file shares, hidden administrative shares and shared printers, type the following command:
net shareYou may have to perform further troubleshooting to determine the causes for multiple client sessions.
Use Network Monitor to find out which component initiates an additional session and what security context is used for the Server Message Block (SMB) session. To filter the traffic that printer spooling causes, use the R_WINSPOOL parser in Network Monitor. If a Windows-based computer looks for computers that are acting as a Print Queue Server, it uses NetShareEnum transactions through the RemAPI protocol (also known as the Microsoft Windows Lanman Remote API Protocol). By default, when you use a NetShareEnum transaction, you require only anonymous access to make NetServerEnum2 and NetServerEnum3 requests. By default, Windows operating systems have anonymous access enabled.
For more information, click the following article number to view the article in the Microsoft Knowledge Base:
(http://support.microsoft.com/kb/122920/ )Inbound connections limit in Windows
(http://support.microsoft.com/kb/132679/ )Local System account and null sessions in Windows NT
(http://support.microsoft.com/kb/143474/ )Restricting information available to anonymous logon users
(http://support.microsoft.com/kb/149522/ )System Error 71 and License Manager
(http://support.microsoft.com/kb/154541/ )Clients open many \Pipe\Spoolss connections to WinNT print server
(http://support.microsoft.com/kb/156431/ )Error 71 when using NT Server from MSDN Select CD
(http://support.microsoft.com/kb/179483/ )"No more connections can be made at this time" error message
(http://support.microsoft.com/kb/191611/ )Symptoms of multihomed browsers
(http://support.microsoft.com/kb/246261/ )How to use the RestrictAnonymous registry value in Windows 2000
(http://support.microsoft.com/kb/289655/ )How to enable null session shares on a Windows 2000-based computer
(http://support.microsoft.com/kb/302099/ )Windows 2000 clients use multiple connections when mapping drives to a single server
(http://support.microsoft.com/kb/314882/ )Inbound connections limit in Windows XP
Article ID: 328459 - Last Review: October 10, 2007 - Revision: 6.3