FIX: Outbound PPTP connections may disconnect after 60 seconds if the ISA Firewall Service is running (831531)

SYMPTOMS

Outbound PPTP connections from a computer that is running Microsoft Internet Security and Acceleration Server (ISA Server) may disconnect after 60 seconds if the ISA Firewall Service is running and the internal network adapter is bound as the first network adapter.

This problem may occur if ISA Server is installed in either Integrated mode or Firewall mode and if the ISA Firewall Service is running. During the first 60 seconds, clients may be able to ping remote hosts and may be able to transfer data through the tunnel until the PPTP connection is disconnected. You may temporarily prevent this problem by stopping the ISA Firewall Service. This problem affects only outbound PPTP connections that are established from the computer that is running ISA Server.

CAUSE

This problem may occur if Network Address Translation (NAT) is applied to all outbound connections when the ISA Firewall Service is running. When ISA Server processes an address change notification, ISA Server may incorrectly unbind SecureNAT from the external interface. This behavior causes all NAT mappings for the interface to expire. A NAT scavenger thread that runs every 60 seconds then deletes these expired mappings. The PPTP tunnel is disconnected because the NAT mappings have been deleted.

However, the PPTP tunnel may remain connected if the computer that is running ISA Server sends a PPTP control message before the remote peer sends a PPTP control message. This behavior re-creates the NAT mapping correctly. Therefore, incoming packets are delivered to the correct port. The NAT mapping is re-created correctly only if the local server sends the first PPTP control message.

RESOLUTION

Prerequisites

You must install ISA Server Service Pack 1 (SP1) before you apply this hotfix.

For additional information about how to obtain the latest ISA Server service pack, click the following article number to view the article in the Microsoft Knowledge Base:

313139 How to obtain the latest Internet Security and Acceleration Server 2000 service pack

Hotfix information

A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Only apply it to systems that are experiencing this specific problem. This hotfix may receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next ISA Server 2000 service pack that contains this hotfix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services telephone numbers and information about support costs, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

Hotfix file information

The English version of this hotfix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel.

   Date         Time   Version       Size     File name
   -------------------------------------------------------
   21-Dec-2003  09:07  3.0.1200.302  178,448  Mspadmin.exe
   21-Dec-2003  09:07  3.0.1200.302  103,184  Msphlpr.dll
   21-Dec-2003  09:07  3.0.1200.302  393,488  W3proxy.exe
   21-Dec-2003  09:07  3.0.1200.302  299,280  Wspsrv.exe

This hotfix also applies to the French, German, Spanish, and Japanese versions of ISA Server.

WORKAROUND

You might be able to avoid this problem, or you might be able to make this problem occur less frequently, by changing the network adapter binding order so that the external network adapter is bound as the first adapter.

Note If the computer that is running ISA Server is operating in a domain, either as a controller or as a member, or is operating as a DNS or WINS name server, do not change the network adapter binding order. This change may interrupt internal communications. Instead, install the hotfix that the "Resolution" section describes.

To change the network adapter binding order, follow these steps:

In Control Panel, open Network and Dial-up Connections.
On the Advanced menu, click Advanced Settings.
On the Adapters and Bindings tab, verify that the external network adapter is the first bound network adapter.
Click OK.

MORE INFORMATION

When you experience this problem, the following event may appear in the system log file on the remote VPN server if the Routing and Remote Access service has been configured to log the maximum amount of information. The average connection time will be approximately one minute. Event Type: Information
Event Source: RemoteAccess
Event Category: None
Event ID: 20048
Date: DD/MM/YYYY
Time: Time
User: N/A
Computer: SERVERNAME
Description:
The user DOMAIN\USERNAME connected on port VPN4-125 on MM/DD/YYYY at HH:MM and disconnected on MM/DD/YYYY at HH:MM. The user was active for 1 minutes 2 seconds. 321 bytes were sent and 5349 bytes were received. The port speed was 10000000. The reason for disconnecting was user request. To make the Routing and Remote Access service log this event, follow these steps on the remote VPN server:

In the Routing and Remote Access Microsoft Management Console (MMC) snap-in, right-click the server name, and then click Properties.
On the Event Logging tab, select Log the maximum amount of information, and then click OK.

For additional information about this issue, click the following article number to view the article in the Microsoft Knowledge Base:

834426 A demand-dial PPTP connection may disconnect every 1 minute and 30 seconds

For additional information about the terminology that is used to describe Microsoft product updates, click the following article number to view the article in the Microsoft Knowledge Base:

824684 Description of the standard terminology that is used to describe Microsoft software updates