Microsoft KB Archive/97559

= How Remote Access Service Processes Datagram Traffic =

Article ID: 97559

Article Last Modified on 10/31/2006

-

APPLIES TO


 * Microsoft Windows NT Server 4.0 Standard Edition
 * Microsoft Windows NT Workstation 4.0 Developer Edition

-



This article was previously published under Q97559



SUMMARY
This article discusses how Remote Access Service (RAS) uses datagrams under Windows NT. The article is divided into the following subjects:


 * Remote RAS Workstation Posts NCB_Add_Group_Name
 * LAN System Sends a Burst of Multicast Datagrams to a Group Name
 * RAS Client Sends a Datagram
 * Remote RAS Workstation Posts NCB_Add_Name
 * LAN System Sends a Datagram to a Unique RAS Client Name

Remote RAS Workstation Posts NCB_Add_Group_Name
Windows NT adds a group name for the domain or the workgroup. Microsoft LAN Manager, by default, adds a group name for the domain name and other domain names (from the LANMAN.INI file). Applications using NetBIOS can add group names as well. The RAS workstation follows these steps:


 * 1) The RAS server checks to see if the group name registered locally already.


 * 1) * If the name is already registered (because another workstation has posted NCB_Add_Group_Name), the RAS server flags the name as registered and does not post NCB_Receive_Datagram.
 * 2) * Otherwise, the group name is not registered and the following steps are performed.
 * 3) The RAS server posts NCB_Add_Group_Name on all available transports (NBF, TCP/IP, etc.).


 * 1) * MaxNames for RAS: There must be enough names to accommodate all the remote clients add request. The default is 255 (the maximum) which should leave plenty of room.
 * 2) * MaxNames for transport: Each transport has a MaxNames entry that may need tuning. It should be set high enough to handle all of the local server names plus all of the remote client NetBIOS names. The NBF transport can be configured in Control Panel using the &quot;Maximize Throughput and Connections&quot; setting. This allows names and sessions to be tuned high without any realistic limit. See the Windows NT documentation for information on default names in the section covering RemoteListen.
 * 3) * If NCB_Add_Group_Name fails on any transport because another system responds with an AddNameResponse frame (meaning that another system has the group name registered as a unique name), then the group is not added on the server or the client workstation.
 * 4) The RAS server posts RcvDgSubmittedperGroupName number of NCB_Receive_Datagrams for the group name.


 * 1) * This has nothing to do with how many NCB_Receive_Datagrams are posted by the remote client. This is handled by the server only. When a client posts NCB_Add_Group_Name or NCB_Add_Name, the RAS server automatically posts NCB_Receive_Datagram for each name, regardless of what the client posts (even if the client does not post anything).
 * 2) * RcvDgSubmittedperGroupName controls how many NCB_Receive_Datagrams are posted by the server for each group name. This is a resource- intensive parameter. Each one takes 1.5K of physical RAM. As soon as one is completed the server automatically posts a new one.

LAN System Sends a Burst of Multicast Datagrams to a Group Name
The RAS server receives a datagram, and handles it as follows:

  Check EnableBroadcast. Default is 0, disabled. (This datagram is not broadcast in example.)

   0 Yes. Drop broadcast (not multicast) datagram and do not forward to remote clients.

1 No. Continue.   Check MulticastForwardRate. Default is 5.

  -1 Drop datagram. Do not forward any broadcast or multicast. This setting is useful to filter out LAN Manager server announcements that use multicast datagrams for domain group names. If you have a large LAN Manager network with many servers, this can use up asynchronous bandwidth.

0 Guarantees delivery of datagram to client.

>0 (1 to 32767) Works as a gate. After the designated number of     seconds, the gate opens and all datagrams arriving at the server are forwarded to remote clients. When the gate is closed, all datagrams are dropped.

NOTE: This parameter is useful for reducing LAN Manager server announcement traffic. On a large network, all the server announcements can look like a steady stream of data flowing over the asynchronous line.   Check DisableMcastFwdWhenSessionTraffic. Default is 1, enabled.

   1 When a client is busy transferring data during a session (a file      copy, for example), multicast datagrams are dropped.

-1 Broadcast datagrams are dropped even if EnableBroadcast is set to 1.

0 Datagrams are always forwarded. This may slow session traffic. 

If all conditions above are correct, the RAS Server is ready to forward the datagram to remote RAS clients, as follows:


 * 1) Check MaxDgBufferedPerGroupName. Default is 10.

Because of the difference between the LAN speed and the asynchronous line speed, datagram traffic must be buffered. The maximum number of datagrams that the RAS server can buffer per group name is controlled by MaxDgBufferedPerGroupName. In the default (10) is used, every 11th datagram is dropped. The maximum is 255. This is a virtual memory parameter, so it is a relatively minor drain on system resources.
 * 1) The RAS server checks to see which clients have the group name registered. It then multiplexes the datagram to each of these remote clients. RAS clients that have NCB_Receive_Datagram posted for that group name receive the datagram.

NOTE: For non-session traffic, set RAS AUTODISCONNECT to 0. Datagram traffic is not counted in the auto-disconnect time-out. Only session traffic is counted. 0 disables auto-disconnecting RAS clients. Also, because of the slow link, workstations probably do not need to post that many NCB_Receive_Datagrams. You should be able to get by with 2 or 3.

RAS Client Sends a Datagram
Check NetbiosGatewayEnabled. Default is 1, enabled.

1 All datagrams sent by remote clients are forwarded onto all transports. The default is all valid networks.

0 Datagrams can only be received by the RAS server if it has an NCB_Receive_Datagram posted for the given name.

Remote RAS Workstation Posts NCB_Add_Name
By default, MS LAN Manager and Windows NT post NCB_Add_Name for the computer name and user identification of the person logging on.


 * 1) The RAS server posts NCB_Add_Group_Name on all available transports (NBF, TCP/IP, etc.).


 * 1) * MaxNames for RAS: There must be enough names to accommodate all the remote clients add request. The default is 255 (the maximum) which should leave plenty of room.
 * 2) * MaxNames for transport: Each transport has a MaxNames entry that may need tuning. It should be set high enough to handle all of the local server names plus all of the remote client NetBIOS names. The NBF transport can be configured in Control Panel using the &quot;Maximize Throughput and Connections&quot; setting. This allows names and sessions to be tuned high without any realistic limit. See the Windows NT documentation for information on default names in the section covering RemoteListen.
 * 3) * If NCB_Add_Group_Name fails on any transport because another system responds with an AddNameResponse frame (meaning that another system has the group name registered as a unique name), then the group is not added on the server or the client workstation.
 * 4) The RAS server posts RcvDgSubmittedperGroupName number of NCB_Receive_Datagrams for that unique name. This has nothing to do with how many NCB_Receive_Datagrams are posted by the remote client. This is handled by the server only. When a client posts NCB_Add_Group_Name or NCB_Add_Name. the RAS server automatically posts NCB_Receive_Datagram for each name regardless of what the client posts (even if the client does not post anything).

LAN System Sends a Datagram to a Unique RAS Client Name

 * 1) The RAS Server receives the datagram, and places it in a buffer. (There is no parameter to control this buffer: all datagrams are buffered.)
 * 2) A new NCB_Receive_Datagram is posted on the server.
 * 3) The RAS Server forwards the datagram from the buffer to the remote client with the unique name posted.

NOTE: Unique name datagrams take priority over group name datagrams. They are forwarded to the client before pending group datagrams. NET LOGON uses unique name, directed datagrams that are given priority over group datagrams.

Reference(s):
See Remote Access Service documentation for the RemoteListen parameter. This gives related information on session based traffic.

Additional query words: prodnt advanced server serial comm modem

Keywords: kbnetwork KB97559

-

[mailto:TECHNET@MICROSOFT.COM Send feedback to Microsoft]

© Microsoft Corporation. All rights reserved.