Browsing & Other Traffic Incur High Costs over ISDN Routers

• Microsoft Windows NT Workstation versions 3.5, 3.51, and 4.0
• Microsoft Windows NT Server versions 3.5, 3.51, and 4.0

SYMPTOMS

Your ISDN TCP/IP router telecommunication connection costs appear to be very high.

This problem occurs if all of the following are true:

• Your network spans two or more sites.
• You use ISDN TCP/IP routers.
• You use an ISDN service that charges you based on connection time.

CAUSE

The following Windows NT features may cause a lot of traffic between domain servers on different sites, causing your ISDN telecommunication costs to be high:

- Domain browsing - Windows Internet Name Service (WINS) replication - Directory replication - User accounts database (SAM) replication - Printer browsing - Other (DHCP, etc.)

You can use Network Monitor to check which of these features cause traffic on your network, including traffic from and to the ISDN router.

How Domain Browsing Causes a lot of Network Traffic

The Windows NT domain master browser (DMB) exchanges computer browse lists with the master browsers (MBRs), usually the backup domain controllers (BDCs), in the other remote networks several times per hour.

In your multi-site company, Microsoft recommends you have at least one BDC at each site. As a result, your company's domain may span multiple sites. This causes browsing network traffic across the your ISDN routers.

Twelve minutes after an MBR boots and every twelve minutes thereafter, the MBR connects to the DMB, that is also the Primary Domain Controller (PDC), by sending a request to the NetBIOS name <domain>0x1b that is owned by the DMB. The MBR then sends the local browse list to, and retrieves the global browse list from, the DMB. This causes the first connection over ISDN and usually lasts several seconds, so this may take up more than one GBE on the ISDN line.

Browsing communication uses RPC over a named pipe connection. After the named pipe connection is closed the logical network connection is still entertained by the redirector for ten more minutes because that is when the MBR redirector's KeepConn parameter expires by default. Although, this logical connection does not incur ISDN router costs, frames sent to disconnect after the ten minute period cause another ISDN connection to be established, which incurs costs.

Two minutes later, 24 minutes after booting, the MBR connects again to the DMB for a browse list exchange. This occurs every twelve minutes. ISDN

RESOLUTION

To correct this problem, upgrade to Windows NT 3.51 (if you have not already done so) and install the latest U.S. Service Pack for Windows NT version 3.51.

To work around this problem, read the sub-section that applies to your traffic problem:

• Working Around the Domain Browsing Problem
• Solving the Domain Browsing Problem with a Fix
• Configuring Other Features That Cause Traffic

Working Around the Domain Browsing Problem

To work around this problem, modify the following parameters in the Windows NT registry and/or configure your ISDN router to turn off during idle hours:

WARNING: Using the Registry Editor incorrectly can cause serious, system- wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of the Registry Editor can be solved. Use this tool at your own risk.

• To minimize ISDN connections with full availability of the domain browse list:

  a. Under the subtree HKEY_LOCAL_MACHINE, locate the following registry

        subkey:
  

           \SYSTEM\CurrentControlSet\Services\LanmanWorkstation\Parameters
  
     b. Set the KeepConn parameter to a small value, for example, five
        seconds.
  
        This prevents network traffic between browse cycles to disconnect
        The connection made during the browse list exchange. Set this
        Parameter on all domain controllers.
  
  

• To further minimize ISDN connections during idle hours, for example, during the night and during the weekend, set a filter option on the ISDN TCP/IP router to turn off the ISDN line during the idle hours.

  NOTE: This results in loss of browse listings of computers on remote sites.

Solving the Domain Browsing Problem with a Fix

To fix this problem, obtain the fix mentioned below from Microsoft Product Support Services. After applying the fix, the browser service accepts the MasterPeriodicity and the BackupPeriodicity parameters to the registry in the KEY_LOCAL_MACHINE subtree under the following subkey:

   \SYSTEM\CurrentControlSet\Services\Browser\Parameters

MasterPeriodicity:

DWORD specifies in seconds how frequently an MBR contacts the DMB. The default is 720 (twelve minutes), the minimum is 300 (five minutes). The maximum is 4,294,967 (or 0x418937 hex), which is 49 days and 8 hours. This parameter can be changed dynamically (without rebooting) with the Registry Editor or REGINI (from the Windows NT Resource Kit). You can schedule REGINI with the scheduler service to reduce browser traffic during the night or over the weekend.

The parameter should be set on each MBR. Because another computer can be elected to be the MBR you should apply the fix to each Windows NT computer in the domain, because they are most likely to win browser elections. For additional information, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID:Q102878
   TITLE     :Information on Browser Operation

BackupPeriodicity:

DWORD specifies in seconds how frequently a backup browser contacts the MBR. The default is 720 (twelve minutes), the minimum is 300 (five minutes). The maximum is 4,294,967 (or 0x418937 hex), which is 49 days and 8 hours. This parameter is not read dynamically so you have to restart your computer. This parameter does not affect the WAN, since this traffic is always on one subnet.

CAUTION: BackupPeriodicity is used to determine when an entry in the browse list has to be deleted. This is done after three periods of BackupPeriodicity. Because of the way dynamic update of MasterPeriodicity is implemented, it is possible you can lose entries in your browse list on the PDC when you change MasterPeriodicity from a high value to something else.

To prevent this you should increase BackupPeriodicity to at least a third of the maximum value of MasterPeriodicity. You must implement this on every computer which can become the PDC.

Configuring Other Features That Cause Traffic

To minimize non-domain browsing traffic, modify the following parameters in WINS Server Admin or the Windows NT registry:

WARNING: Using the Registry Editor incorrectly can cause serious, system- wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of the Registry Editor can be solved. Use this tool at your own risk.

• For WINS replication, the interval is configurable in WINS Server Admin.
• The following services are configurable in the Windows NT registry under the subtree HKEY_LOCAL_MACHINE:

  - For directory replication, the interval is configurable with the

       Interval parameter in the subkey:
  

           \CurrentControlSet\Services\Replicator
  
     - For SAM replication, the interval is configurable with the
       PulseMaximum parameter in the subkey:
  
          \CurrentControlSet\Services\Netlogon
  
     - For printer browsing, the interval is configurable with the
       DisableServerThread parameter in the subkey:
  
          \CurrentControlSet\Control\Print
  
  

STATUS

Microsoft has confirmed the domain browsing to be a problem in Windows NT versions 3.5 and 3.51. This problem has been corrected in the latest U.S. Service Pack for Windows NT version 3.51. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

   S E R V P A C K