Troubleshoot Interface CRC Errors on IOS XR Routers

Introduction

This document describes how to troubleshoot Cyclic Redundancy Check (CRC) errors on interfaces within Cisco IOS XR routers. Cisco recommends knowledge of the Cisco IOS XR platform and admin CLI access. Applicable platforms include ASR 9000 Series Routers (ASR 9006, ASR 9010), NCS 540/560/5500/5700 Series Routers.

Problem

Cisco IOS XR platforms leverage CRC checks on physical interfaces (Ethernet, optical, and so on) to maintain link reliability, and provide interface statistics that include CRC error counters. High CRC error counts typically indicate physical layer issues such as faulty cables, connectors, or transceivers. On platforms like the NCS 5500/5700 Series and ASR 9000 Series, CRC error trends can trigger alarms or automated workflows to minimize downtime.

Common Causes of Interface CRC Errors

• Configuration mismatches: such as Maximum Transmission Unit (MTU) size mismatches between devices, which can cause large packets to be truncated incorrectly, leading to CRC errors.
• Physical media faults: damaged fiber, copper or DAC cables, dirty connectors, or failing transceivers.

Procedure to Resolve Interface CRC Errors

1. Verify MTU Settings

Check the MTU configured on the interface of the local router and the connected peer device. While less common for CRC errors than physical issues, an MTU mismatch can sometimes lead to frame truncation and subsequent CRC errors.

2. Inspect and Replace Physical Media

• Visually inspect the cable (fiber, copper, DAC) for any damage, kinks, or sharp bends.
• Ensure the cable is securely seated in both the router interface and the connected device.
• Action: replace the cable with a known good one.

3. Use External Loopback

Use external loopback sensibly to identify the hardware that is causing CRC. If CRC errors stop, the issue is likely further upstream (for example, remote device, cable). If they continue, the transceiver or the port hardware is suspect.

4. Move Interface to a Different Port/Line Card

• If possible, move the cable and transceiver to a different port on the same line card. If errors persist, the line card itself can be faulty.
• If errors stop, the original port was likely defective.

5. Check Known Software Issues

• Search the Cisco Bug Search Tool (BST) for your platform, interface type, and software version.
• Review Cisco Field Notices, Release Notes, and known Caveats.

Products Covered

• ASR 9000 Series Aggregation Services Routers
• Network Convergence System 500/540/560/5000 Series Routers

原文链接：https://www.cisco.com/c/en/us/support/docs/routers/asr-9000-series-aggregation-services-routers/225385-troubleshoot-interface-crc-errors-on.html