Cisco WAN Switching Modules

Document ID: 10865

Contents

Introduction
Prerequisites
      Requirements
      Components Used
      Conventions
Error Definition
Error Example
Troubleshoot
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Related Information

Introduction

This document discusses information you can use to troubleshoot broadband trunk module (BTM) Rx Spacer Pkt Drp errors.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

This document is not restricted to specific software and hardware versions.

Conventions

For more information on document conventions, refer to the Cisco Technical Tips Conventions.

Error Definition

This error applies to the IGX BTM with E1, E2, E3, and T3 backcards.

The BTM maintains a receive spacer queue per traffic type to shape the rate of traffic toward the IGX bus. For T3, receive spacer queues buffer ATM cells that enter the IGX on a T3 trunk and exit the IGX as FastPackets on a T1 trunk. Cells can enter the IGX faster than the network trunk module (NTM) can send them. Spacer queues buffer packets, which allows the BTM to feed them to the IGX bus at a rate the NTM can accept. When the receive spacer queue becomes congested, packets drop after traffic bursts and when the:

• Available receive spacer queues are full.

  -or-

• Switch software programs a single receive-spacer queue instead of one queue per traffic type.

Error Example

The likely location of equipment errors is highlighted in yellow.

Troubleshoot

Complete these steps in order to troubleshoot the Rx Spacer Pkt Drp error.

1. Verify that trunk utilization does not cause Rx Spacer Pkt Drp errors.

2. Use the clrtrkerrs command to frequently clear trunk error statistics.

3. When dsptrkerrs shows Rx Spacer Pkt Drp errors, use the dsptrkutl command to find real-time utilization of trunks.

4. Look at the Peak Interval Utilization field. If the value that displays is higher than 85 percent, which indicates high trunk utilization, Rx Spacer Pkt Drp errors likely occur because of queue overflows.

For immediate help, reduce the amount of traffic that runs over the trunk.

1. Verify that enough additional bandwidth exists on the network or on the IGX to reroute connections off of the BTM trunk that experiences the Rx Spacer Pkt Drp errors.

2. Issue the dspload command to evaluate all trunks on the IGX.

3. If sufficient bandwidth exists, issue the cnftrk command.

4. Increase the Statistical Reserve to just below the value of the available bandwidth on the other trunks. This forces connections away from the target BTM trunk. This also decreases congestion in the spacer queue, which stops the discards.

Note: If a connection fails, sufficient trunk bandwidth may not exist to route the connection after you have increased the BTM Statistical Reserve. You might need to slightly decrease the BTM trunk Statistical Reserve in order to restore the connection.

If the problem persists after you perform these troubleshooting steps, contact Cisco Technical Support at (800) 553-24HR, (408) 526-7209, the Cisco Technical Support Website, or send an E-mail to tac@cisco.com.

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Related Information

• More BTM Trunk Alarm Types
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• Cisco WAN Switching Solutions - Cisco Documentation
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• Software Center - WAN Switching Software
• Technical Support - Cisco Systems