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Adjusting PPTP KeepAlive Frequency

This article was previously published under Q193841
This article has been archived. It is offered "as is" and will no longer be updated.
IMPORTANT: This article contains information about editing the registry.Before you edit the registry, make sure you understand how to restore it ifa problem occurs. For information on how to do this, view the "Restoringthe Registry" online Help topic in Regedit.exe or the "Restoring a RegistryKey" online Help topic in Regedt32.exe.
Some ISDN Connected Clients/Networks that use PPTP may notice high costsassociated with continuos ISDN link caused by the idle inactivity timernever expiring. This PPTP keepalive packet can be controlled to reduce thefrequency of this test so that it is greater than the idle inactivitytimeout value. PPTP, by default, sends "keepalive" packet every 60 secondsto verify the tunnel. This frequency can be adjusted by altering theregistry.
The keepalive traffic consists of an echo request and an echo reply. Whenthere is no traffic through the tunnel for 60 seconds, the client sends anecho request to confirm the validity of the tunnel. To confirm that thesekeepalive packets are being sent, the user can use Network Monitor to parsethe traffic.

The packets look like the following:
   PPTP: Control Packet (1): Echo Request (5)				
   PPTP: Control Packet (1): Echo Reply (6)				

Please note the release version of Network Monitor has to be altered tocorrectly display the PPTP packets. For additional information, please seethe following article in the Microsoft Knowledge Base:

164601How to Enable PPTP Port for Network Monitor

This must be set at both ends of the connection to limit the "tunnel test"

The InactivityIdleSeconds registry setting starts a timer that measures thenumber of seconds between packets. When the timer reaches the default of 60seconds, it instructs the system to send a control channel packet to theserver. The EchoReplyTimeoutSeconds registry setting defines how long theclient will wait for a response to the echo request.

WARNING: Using Registry Editor incorrectly can cause serious problems thatmay require you to reinstall your operating system. Microsoft cannotguarantee that problems resulting from the incorrect use of Registry Editorcan be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys AndValues" Help topic in Registry Editor (Regedit.exe) or the "Add and DeleteInformation in the Registry" and "Edit Registry Data" Help topics inRegedt32.exe. Note that you should back up the registry before you edit it.If you are running Windows NT, you should also update your Emergency RepairDisk (ERD).

To alter the default, the user must add the following registry parametersto the system.
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Raspptpe\Parameters \Configuration\

InactivityIdleSeconds: REG_DWORD: default: 60 Number of seconds PPTP will go with no activity on the control channel.

EchoReplyTimeoutSeconds: REG_DWORD: default: 60 Number of seconds PPTP will wait for a reply from an echo request. If reply is not received, PPTP drops the connection.
For additional information, please see the following article in theMicrosoft Knowledge Base:

164601How to Enable PPTP Port for Network Monitor

181431How Windows NT RAS Handles Auto Disconnect

Article ID: 193841 - Last Review: 12/05/2015 09:25:01 - Revision: 1.1

Microsoft Windows NT Server 4.0 Enterprise Edition, Microsoft Windows NT Workstation 4.0 Developer Edition, Microsoft Windows NT Server 4.0 Standard Edition

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