Cisco BPX/IGX/IPX WAN Software

April 29, 1999

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Products Affected

Problem Description

Permanent virtual circuits (PVCs) will not reroute around an inter-node trunk in the communications failure (Comm Fail) state. This occurs because the node parameter for enabling reroute on communications failure (Comm Fail) defaults to "No" after a switch software upgrade to 9.1.06 or later. This parameter is set to "No" intentionally. At the earliest opportunity after the initial introduction of software version 9.1.06 or later to the network (whether by upgrade or initial installation), the parameter should be set to "Y" in most networks.

Problem Symptoms

The network user will not experience any negative side effects unless the trunk is indeed in Comm Fail state for reasons unrelated to control traffic flooding and the PVCs to which the user is subscribed are routed over the trunk in the Comm Fail state.

Trunk failures other than Comm Fail, such as Loss of Signal (LOS), Loss of Frame (LOF), Remote Alarm Indication (RAI) (also known as Yellow Alarm), and exceeding Major Alarm thresholds for statistical alarms will still result in declared trunk failures. In these failure instances, PVCs will still be rerouted around the failed trunk.

The network engineer would observe PVCs routed over trunks in the Comm Fail state. Use the dsptrks command to find the failed trunks, and then use the dspcon or dsprts command to see connections routed over the trunks in Comm Fail.

Background

The ability to disable or enable PVC rerouting on Comm Fail detection was introduced to allow network engineers the ability to prevent network control messages from affecting user traffic. Under certain conditions, network message "flooding" may cause the false detection of a Comm Fail on a trunk when an actual Comm Fail condition does not exist. The detection of the Comm Fail will cause PVCs to reroute to other trunks or, if no additional trunk bandwidth is available, the PVCs will fail.

It should be noted that the default to "No" for this feature is intentional and the feature works as designed. Reroute on Comm Fail should be set to "Y" in most networks. The Reroute on Comm Fail parameter may be set to "No" in networks that have frequent link layer problems on inter-node trunks.

Workaround/Solution

The workaround and solution are the same.

• For the BPX, re-enable the parameter by using the cnfnodeparm 43 y command.

• For the IPX and IGX, re-enable the parameter by using the cnfnodeparm 41 y command.

For More Information

If you require further assistance, or if you have any further questions regarding this field notice, please contact the Cisco Systems Technical Assistance Center (TAC) by one of the following methods:

• Open a service request on Cisco.com
• By email
• By telephone