Cisco WAN Switching Modules

Document ID: 6439

Contents

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

Introduction

This document describes the Network Trunk Module (NTM) logged Comm Fail error, which applies to the IGX NTM with T1, E1, and subrate (SR) back cards.

Prerequisites

Requirements

Readers of this document should be knowledgeable of the following:

• IGX switch

• NPM (Network Processor Module)

• NTM card with T1, E1, and SR back cards

Components Used

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

Conventions

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

Error Definition

The NTM logs a Comm Fail error when the communication failure test fails. The IGX NPM uses the Comm Fail test to verify whether a trunk is usable for communication between nodes using the same trunk.

The communication failure test runs on each NTM trunk independently. The test interval and timeout parameters are configured using the SuperUser-level cnfnodeparm command. The communication failure test is initiated by the NPM, which sends a packet or stream of packets filled with a test pattern over the target trunk to the distant-end NPM. Depending upon test results, the following occurs:

• If the packet is correctly received by the distant-end NPM, an acknowledgment goes to the originating NPM over the target trunk.

• If the originating NPM receives the acknowledgment that contains correct information about node number and trunk number matching the local topology map, then the communication failure test passes.

• If the originating NPM does not receive the acknowledgment within a timeout period, the communication failure test is reattempted.

• If a number of retries fails, the trunk fails the communication failure test. The originating NPM declares the trunk in Comm Fail, which is an integrated alarm. A trunk experiencing Comm Fail may try to reroute all connections, depending upon the setting of the Enable Rrt on Comm Fail parameter of the cnfnodeparm command.

• If a trunk is in Comm Fail, the test must pass at both ends before the failure clears.

Note: Do not confuse a Comm Fail test with a communication break (Comm Break) test. The Comm Break test is used for nodes that are unable to communicate with each other and seek to reestablish communication. A Comm Fail could result in a Comm Break between network nodes.

Configure the parameters of the Comm Fail test using the cnfnodeparm command parameters described in the following table:

Caution: Default values for Comm Fail test parameters are optimized to ensure node and network function. Do not change values without verifying them in a laboratory environment.

Use the cnfcftst command to configure the test pattern used by the NPM for the communication failure test. Changing the test pattern can often detect pattern-sensitive trunk problems.

Examples of possible causes for Comm Fails and Comm Breaks include the following:

• Carrier and cable problems

• Trunk card malfunction

• Processor card malfunction

• Hardware

• Configuration mismatches

Error Example

The following illustration shows the likely location of equipment errors in yellow:

Troubleshooting

Complete the following steps to troubleshoot the Comm Fail error:

1. Use the Service-level on1 command to verify that Comm Fail Test is enabled.

2. Use the procedures described in Troubleshooting Problems When Adding a Trunk to isolate the problem.

3. If the problem persists, contact Cisco Systems TAC.

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Related Information

• Real-Time Throttling Mechanisms in IPX/IGX Switch Software
• How to Distinguish Between Different IGX NTM Models
• WAN Switching Network Synchronization Fundamentals
• International Telephony Union (ITU) Recommendation G.704
• Cisco WAN Switching Solutions – Cisco Documentation
• Guide to New Names and Colors for WAN Switching Products
• Downloads – WAN Switching Software
• Technical Support – Cisco Systems