Field Notice: FN63944 - ASR 920 1G Ports Do Not Come Up on Cisco IOS Software Release 15.5(1)S (3.14.0) - Software Upgrade Recommended
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Notice
THIS FIELD NOTICE IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTY OF MERCHANTABILITY. YOUR USE OF THE INFORMATION ON THE FIELD NOTICE OR MATERIALS LINKED FROM THE FIELD NOTICE IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS FIELD NOTICE AT ANY TIME.
Products Affected
| Affected Product Name | Description | Comments |
|---|---|---|
| ASR-920-24SZ-IM= | Cisco ASR920 Series - 24GE and 4-10GE : Modular PSU and IM | |
| ASR-920-24SZ-M= | Cisco ASR920 Series - 24GE Fiber and 4-10GE : Modular PSU |
Defect Information
| Defect ID | Headline |
| CSCvs18851 | Router goes into a continuous boot-loop when downgraded from newer to older versions. |
Problem Description
The 1G ports on ASR 920 Routers ASR-920-24SZ-IM and ASR-920-24SZ-M do not come up when operating with Cisco IOS Software Release 15.5(1)S (3.14.0).
Background
Cisco discovered that the 1G ports on ASR 920 Routers ASR-920-24SZ-IM and ASR-920-24SZ-M do not operate when you boot it with Cisco IOS Software Release 15.5(1)S (3.14.0).
This issue occurs due to a mismatch between the hardware version programmed in the device and the version expected by the Cisco IOS software.
Problem Symptom
Symptom 1
The 1G ports on the ASR 920 Routers ASR-920-24SZ-IM and ASR-920-24SZ-M that have Cisco IOS Software Release 15.5(1)S (3.14.0) installed do not come up.
Enter the show platform command, which provides output as shown here:
Slot CPLD Version Firmware Version ---- ------------ ---------------- R0 01491800 15.4(3r)S4
If the highlighted Least Significant Bit (LSB) value is 00 then the router is impacted. If this LSB is greater / equal to 1 then the router is not impacted.
Symptom 2
When a copper Small Form-Factor Pluggable (SFP) is used on the 1G port and connected to another router, the physical layer line comes up, but no further traffic is processed; neither ICMP pings nor Cisco Discovery Protocol (CDP) packets are transmitted.
Workaround/Solution
Cisco recommends that customers migrate to Cisco IOS Software Release 15.5(1)S1 (3.14.1) or later in order to overcome this issue.
How to Upgrade Software
The steps to upgrade to the latest Cisco IOS version for the ASR 920 router can be found at Installing and Upgrading Software.
See the 'Upgrading the Router Software' section in the previous link, which provides detailed instructions on how to download and upgrade to the latest Cisco IOS version.
How to Identify Affected Products
To determine whether a unit is affected, refer to the Serial Number Validation section of this Field Notice.
Serial Number Validation
The Cisco Support Assistant (CSA) can help verify whether a device is impacted by the issue that is described in this Field Notice. To check the device, either enter the serial number in the CSA on the right side of this page or click the following URL: Cisco Support Assistant
Revision History
| Version | Description | Section | Date |
| 10.2 | Updated the link for the Serial Number Validation tool. | Serial Number Validation | 2026-JUL-16 |
| 10.1 | Updated the Defect Information Section | — | 2019-MAR-18 |
| 10.0 | Migration to new field notice system | — | 2017-OCT-13 |
For More Information
For further assistance or for more information about this field notice, contact the Cisco Technical Assistance Center (TAC) using one of the following methods:
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