A computer running SNA Server on an Ethernet network that has an 802.2 DLCconnection configured to communicate with a remote device (AS/400, 3174, or3745, for example) on a Token Ring may exhibit the following symptoms:
The 802.2 DLC Connection configured in SNA Server Admin stays in a perpetual "Pending" state.
The Windows NT Application Event Log on the SNA Server does not contain any events that indicate connection activation problems. The Application Log will usually contain an Event 230 or an Event 23 when an 802.2 DLC connection fails to activate.
A Network General Sniffer(TM) or Microsoft Network Monitor trace on the Ethernet segment of the computer running SNA Server shows an XID exchange that never completes. The computer running SNA Server never receives the SABME mode setting command from the remote system to indicate the end of the XID exchange.
This problem has been observed when SNA Server is connected to the remotesystem across a Cisco router which is configured for LLC LocalAcknowledgment. The Cisco router fails to forward the SABME command sent bythe remote device (for example, IBM 3745) to SNA Server, causing theconnection to fail to activate. The result is that the SNA Server restartsthe XID process by sending a pre-negotiation XID to the remote device. Thisprocess continues indefinitely.
To work around this problem:
Disable Local Acknowledgment on the Cisco router(s) between the Ethernet and Token Ring.
In an LLC (802.2 DLC) session, when Device A sends a frame to Device B,Device A expects Device B to respond before the T1 timer expires. In a WANenvironment that contains slow links, it is possible to see the T1 timerexpire before a response was received causing retransmissions. Cisco'sLocal Acknowledgment feature attempts to solve this problem by splittingthe LLC session between the two devices. If Local Acknowledgment isconfigured, the LLC session between two two devices is not end-to-end butinstead terminates at the local router(s). The LLC session with Device Aends at the Router as does the LLC session with Device B. The router thenresponds to the frames sent from Devices A and B instead of having theactual device send the response. When this feature is enabled, all LLCsupervisory frames (RR, RNR, REJ) from one of the devices go no fartherthan the router since the router will respond to them on behalf of theother device.
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For additional information on SNA Server and 802.2 Connection Timers,please see the following article in theMicrosoft Knowledge Base:
129786 SNA Server and 802.2 Connection Timers (t1, t2, ti)
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