TEST/XID Retries not Configurable for DLC Connections

• Microsoft SNA Server, version 2.0, 2.1, 2.11, 3.0, and 3.0 SP1

SYMPTOMS

When SNA Server tries to activate an 802.2 DLC connection, LLC TEST frames are sent to the remote network address to initiate the link level connection. If the remote station is not replying to the TEST frames, a network trace will show that SNA Server continues to send additional TEST frames. Each time the SNA Server service submits an Open(Link) Request to the 802.2 DLC Link Service, it generates TEST frames to test the connection.

For additional information on how SNA Server initiates 802.2 DLC connections, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q123791
   TITLE     : SNA Server Remote Station Discovery Process

SNA Server uses the same algorithm for XID retries, so the number of XID retries equals the number of TEST frame retries per Open(Link) Request.

CAUSE

The number of TEST and XID command retries per Open(Link) Request is hardcoded for the 802.2 DLC link service. The retry interval is also hardcoded. When an Open(Link) Request is submitted to the link service, a local TEST command is sent out on the local network segment. If SNA Server does not receive a reply to the local TEST command within 0.5 seconds, it sends an all-routes broadcast TEST command. The link service will send a total of three all-routes broadcast TEST commands if the remote station it not responding. The retry interval between the all-routes broadcast TEST commands is 15 seconds. This sequence is repeated for each Open(Link) Request that the 802.2 DLC Link Service receives from the SNA Server service.

The following is network trace captured using Microsoft's Network Monitor that shows the sequence of TEST commands for one Open(Link) Request:

   Frame  Time    Source  Dest  Protocol  Description   

   1      0.000   Server  Host  LLC       TEST DSAP=0x00 SSAP=0x04 C POLL                                                                    
   2      0.001   Server  Host  SNA       SNA Packet: Req:(FMD)(SD)                                                                          
   3      0.731   Server  Host  LLC       TEST DSAP=0x00 SSAP=0x04 C POLL                                                                    
   4      0.000   Server  Host  SNA       SNA Packet: Req:(FMD)(SD)                                                                          
   5      18.893  Server  Host  LLC       TEST DSAP=0x00 SSAP=0x04 C POLL                                                                    
   6      0.000   Server  Host  SNA       SNA Packet: Req:(FMD)(SD)                                                                          
   7      18.892  Server  Host  LLC       TEST DSAP=0x00 SSAP=0x04 C POLL                                                                    
   8      0.000   Server  Host  SNA       SNA Packet: Req:(FMD)(SD)   

   ARTICLE-ID: Q123791
   TITLE: SNA Server Remote Station Discovery Process

If this sample trace had been taken on a Token Ring network, it would have the "all-routes broadcast" setting specified for the TEST commands in frames 3, 5, and 7. Ethernet does not contain any source-routing information, therefore the "all-routes broadcast" setting does not exist.

A trace that captures the XID frames sent by the SNA Server will show the same number of retries and retry intervals as it does for TEST frames.

RESOLUTION

The 802.2 DLC Link Service for SNA Server has been updated to allow the number of retries and the retry interval to be configured for TEST and XID commands. In addition, the following registry entries have to be added to change the number of retries and the retry interval for the TEST and XID commands:

   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\<SNADLCx>\Parameters
   \ExtraParameters

   Value Name: TestTimeout 
      <- Used to specify the local TEST/XID timeout in seconds.
   Data Type: REG_DWORD
   Data: <1 - 127 (decimal)>  

   Value Name: XidTimeout
      <- Used to specify the all-routes broadcast TEST/XID timeout in seconds.
   Data Type: REG_DWORD
   Data: <1 - 127 (decimal)>   

   Value Name: TestRetries
      <- Used to specify the number of TEST/XID retries.
   Data Type: REG_DWORD
   Data: <0 - 254 (decimal)>     

STATUS

Microsoft has confirmed this to be a problem in SNA Server versions 2.0, 2.1, 2.11 (all SPs), 3.0, and 3.0 SP1. A supported fix is now available, but has not been fully regression-tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Product Support Services for more information.