WAN and Trust: Traffic on the Wire

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Summary

This article describes a new feature that is included in Windows NT 3.51 Service Pack 5. This feature is designed to allow you to reduce network traffic related to Windows NT trust relationship polling over a wide area network (WAN) using perhaps a leased line (for example, an ISDN or X.25 line) where the leased line provider charges by the amount of network traffic. Trust relationship polling occurs between domain controllers (DCs) to establish a secure channel.

In Windows NT 3.51 without this new feature, if the secure channel cannot be established, it is retried every 15 minutes. With this new feature installed you can control the intervals between which a DC sends discovery packets in search of a DC of a trusted domain.

Microsoft has made a fix in Netlogon.dll so that you can increase the time between retries and you can increase the time in which NETLOGON assumes a DC is reachable (ScavengeInterval and ExpectedDialupDelay).



When Windows NT Uses Polling Between Domain Controllers

In Windows NT 3.51, once a secure channel to a trusted domain has been established (that is, after the DC in domain_A found a DC in the trusted domain_B), Windows NT does not continue to poll the secure channel to make sure the secure channel is still available.

If, however, the DC is contacted for some other reason, for example, if a user logs on and a pass-through authentication to the other domain is required, the first DC needs to contact the second DC again and network polling of the secure channel starts for this reason once again and stops after the the pass-through authentication is completed.

Regular network traffic packets are not caused by trust relationship polling of the secure channel, so if you frequently observe frames related to trust relationship traffic on your WAN router, it is probably caused by an unreliable WAN in which case this new feature helps you reduce this type of network traffic.

NETLOGON Debug Output Samples

The following sections numbered 1, 2, 3, and 4 are about the NETLOGON debug output that appears when trusts are involved:
  1. The following NETLOGON debug-output is from a primary domain controller (PDC) of the trusting domain that cannot find a DC in the trusted domain (the network cable is disconnected):



    00:00:00 NlInitTrustList: MASTERDOM in LSA
    00:00:00 NlUpdateTrustListBySid: MASTERDOM: Added to local trust list
    00:00:00 NlDcDiscoveryMachine: MASTERDOM: Start Discovery
    00:00:05 NlDcDiscoveryMachine: MASTERDOM: Discovery retry 1
    00:00:10 NlDcDiscoveryMachine: MASTERDOM: Discovery retry 2
    00:15:00 NlDcDiscoveryMachine: MASTERDOM: Start Discovery
    00:30:00 NlDcDiscoveryMachine: MASTERDOM: Start Discovery


    The above frames show that the PDC tries to find the DC by calling NlDcDiscoveryMachine three times and waits five seconds between each retry.



    After these three retries the Scavenger Timer causes NETLOGON to look for the trusted domain again every 15 minutes. Here are some of the frames that appear (sent by the PDC of the trusting domain):

       *BROADCAST    NBT NS: Query req. for MASTERDOM <1C>: check to find a
                     trusted domain DC


    Because the PDC cannot find a DC by broadcasting the PDC starts using WINS:
       *BROADCAST   ARP_RARP  ARP: Request, Target IP: 191.60.0.1:   find the
                    router to get to WINS
  2. The PDC of the trusting domain can find a DC in the trusted domain:

    NETLOGON debug output:

       00:00:00 NlInitTrustList: domainname in LSA
       00:00:00 NlUpdateTrustListBySid: domainname: Added to local trust list
       00:00:00 NlDcDiscoveryMachine: domainname: Start Discovery
       00:00:00 NlDcDiscoveryMachine: MASTERDOM: Found DC \\D-SPOCK on
          transport \Device\NetBT_Lance1
    
       00:00:00 NlDcDiscoveryMachine: MASTERDOM: DC \\D-KIRK ignored. DC
          previously found.
    
       00:00:00 NlDcDiscoveryMachine: MASTERDOM: DC \\NTD-UHURA ignored. DC
          previously found.
    
       00:00:00 NlDcDiscoveryMachine: MASTERDOM: DC \\D-MCKOY ignored. DC
          previously found.


    Here are some of the frames that appear (sent by the PDC of the trusting domain to the DC of the trusted domain):
       NETLOGON  SAM LOGON request from client   RESCTL1       D-KIRK
       NETLOGON  SAM LOGON request from client   RESCTL1       D-SPOCK
       NETLOGON  SAM LOGON request from client   RESCTL1
       NETLOGON  SAM LOGON request from client   RESCTL1       D-MCKOY
       NETLOGON  SAM Response to SAM LOGON request  D-SPOCK         RESCTL1
       NETLOGON  SAM LOGON request from client   RESCTL1       191.60.19.243
       NETLOGON  SAM Response to SAM LOGON request  D-KIRK          RESCTL1
       NETLOGON  SAM LOGON request from client   RESCTL1       NTD-UHURA
       NETLOGON  SAM Response to SAM LOGON request  NTD-UHURA       RESCTL1
       NETLOGON  SAM Response to SAM LOGON request  D-MCKOY         RESCTL1
  3. After the trust setup fails once because the cable is purposely disconnected, the following NETLOGON debug-output occurs with the cable reconnected. The PDC tries to log on to the trusted domain:

       00:00  NlSessionSetup: MASTERDOM Try Session setup
       00:00 NlStartApiClientSession: MASTERDOM: Bind to server \\D-SPOCK.
       00:00 NlSetStatusClientSession: MASTERDOM: Set connection status to 0
       00:00 NlSessionSetup: MASTERDOM Session setup Succeeded


    Here are some of the frames sent between trusting PDC and trusted DC:
       R_LOGON   RPC Client call logon:NetrServerReqChallenge(..)
       R_LOGON   RPC Server response logon:NetrServerReqChallenge(..)
       R_LOGON   RPC Client call logon:NetrServerAuthenticate2(..)
       R_LOGON   RPC Server response logon:NetrServerAuthenticate2(..)
       R_LOGON   RPC Client call logon:NetrLogonSamLogon(..)
       R_LOGON   RPC Server response logon:NetrLogonSamLogon(..)
       R_LOGON   RPC Client call logon:NetrLogonSamLogoff(..)
       R_LOGON   RPC Server response logon:NetrLogonSamLogoff(..)
       NETLOGON  SAM LOGON request from client   RESCTL1       D-MCKOY
       NETLOGON  SAM LOGON request from client   RESCTL1       D-KIRK
       NETLOGON  SAM LOGON request from client   RESCTL1       NTHANSJUS
  4. After the trust is established, the connection to the trusted domain is timed out (internally in NETLOGON):

       00:00:00 NlTimeoutApiClientSession Called
       00:00:45 NlTimeoutApiClientSession Called
       00:01:30 NlTimeoutApiClientSession Called
       00:02:15 NlTimeoutApiClientSession Called
       00:02:15 NlTimeoutApiClientSession: MASTERDOM: Unbind from server \\D-
          SPOCK.
    
       00:03:00 NlTimeoutApiClientSession Called
    
    This causes only the following frames to appear on the network:
    
       SMB       C close file, FID = 0x805 RESCTL1       D-SPOCK         IP
       SMB       R close file  D-SPOCK         RESCTL1       IP
       RESCTL1      D-SPOCK        TCP       .A...., len:    0, seq:   7004192,
       ack:
       422155081, win: 7883, src RESCTL1       D-SPOCK         IP


    The DC calls NlTimeoutApiClientSession every 45 seconds.



    And finally the PDC drops the connection to the trusted DC by closing the named pipe.

    NOTE: The PDC does not drop the secure channel and therefore does not have to rediscover the DC in the trusted domain. This saves the PDC scavenger from having to look for the DC every 15 minutes.

Status

Microsoft has confirmed this to be a problem in SNA Server for Windows NT version 3.51.



This problem was corrected in the latest Windows NT 3.51 U.S. Service Pack. 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

Properties

Article ID: 152719 - Last Review: October 26, 2013 - Revision: 5.0
Applies to
  • Microsoft Windows NT Workstation 3.51
  • Microsoft Windows NT Server 3.51
Keywords: 
kbnosurvey kbarchive KB152719

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