SNA Server 802.2 Connection Stays in Pending State

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Symptoms

A computer running SNA Server on an Ethernet network that has an 802.2 DLC connection configured to communicate with a remote device (AS/400, 3174, or 3745, 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.

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Cause

This problem has been observed when SNA Server is connected to the remote system across a Cisco router which is configured for LLC Local Acknowledgment. The Cisco router fails to forward the SABME command sent by the remote device (for example, IBM 3745) to SNA Server, causing the connection to fail to activate. The result is that the SNA Server restarts the XID process by sending a pre-negotiation XID to the remote device. This process continues indefinitely.

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Resolution

To work around this problem:

Disable Local Acknowledgment on the Cisco router(s) between the Ethernet and Token Ring.

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More Information

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 WAN environment that contains slow links, it is possible to see the T1 timer expire before a response was received causing retransmissions. Cisco's Local Acknowledgment feature attempts to solve this problem by splitting the LLC session between the two devices. If Local Acknowledgment is configured, the LLC session between two two devices is not end-to-end but instead terminates at the local router(s). The LLC session with Device A ends at the Router as does the LLC session with Device B. The router then responds to the frames sent from Devices A and B instead of having the actual device send the response. When this feature is enabled, all LLC supervisory frames (RR, RNR, REJ) from one of the devices go no farther than the router since the router will respond to them on behalf of the other device.

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