This document discusses some of the most common hardware failures you
can encounter with the Cisco uBR9xx series cable modems and provides ways to
troubleshoot those failures. The document lists the most common symptoms that
cable modems encounter. The document also walks you through a series of
interactive steps that you can take to narrow down the failure. The purpose of
this document is to enable you to troubleshoot the cable modem yourself in
order to rule out hardware issues.
Note: Refer to Cisco
Cable Voice Adapters (CVA120) Basic Installation and Troubleshooting for
information on how to troubleshoot specific issues with Cisco Cable Voice
There are no specific requirements for this document.
The information in this document is based on the Cisco uBR9xx Series
The information in this document was created from the devices in a
specific lab environment. All of the devices used in this document started with
a cleared (default) configuration. If your network is live, make sure that you
understand the potential impact of any command.
Technical Tips Conventions for more information on document
This Troubleshooting Flowchart
identifies the common failures that Cisco uBR9xx Cable Modems can
These are the four common failures that Cisco uBR9xx Cable Modems can
Note: When you troubleshoot, you must check for any existing field notices
that can affect your cable modem. Refer to the Broadband Cable section of
Product Field Notice
Summary for more information.
Use the Troubleshooting Flowchart to
match the symptom that your cable modem encounters. Then answer 'yes' or 'no'
to navigate down the chart to the correct field. Also refer to the relevant
sections in this document for additional information.
When your cable modem does not boot, the first thing you need to check
is whether the OK LED on the cable modem is lit.
If the OK LED is not lit, ensure that you turn on the power to the
cable modem. If the power is on but the OK LED is still not lit, the cable
modem is probably faulty. Refer to the
Installation Guide for the corresponding cable modem to look up LED
self-test failure codes.
If the OK LED is ON or blinks, connect a console to the cable modem
and issue the show version command to verify whether
the cable modem has the correct Cisco IOS® Software.
If the OK LED is OFF but the self-test failure codes indicate no
failure, the OK LED can be faulty.
Note: Refer to
Series Cable Access Routers for information on console port connection
to the cable modem. Select the appropriate router platform., select the
Hardware Installation Guide, and click on the Connector and Cable
This is the output of a show version command
from a Cisco uBR924 router:
Cisco Internetwork Operating System Software
IOS (tm) 920 Software (UBR920-K8V6Y5-M), Version 12.2(5), RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2001 by cisco Systems, Inc.
Compiled Wed 12-Sep-01 03:33 by pwade
Image text-base: 0x800100A0, data-base: 0x806AE948
ROM: System Bootstrap, Version 12.0(6r)T3, RELEASE SOFTWARE (fc1)
el-vulpix uptime is 1 day, 2 hours, 7 minutes
System returned to ROM by reload at 22:37:37 - Wed Nov 14 2001
System restarted at 22:38:44 - Wed Nov 14 2001
System image file is "flash:ubr920-k8v6y5-mz.122-5.bin"
cisco uBR920 CM (MPC850) processor (revision 3.e) with 15872K/1024K bytes of me.
Processor board ID FAA0418Q0Z2
1 Ethernet/IEEE 802.3 interface(s)
1 Cable Modem network interface(s)
3968K bytes of processor board System flash (Read/Write)
1536K bytes of processor board Boot flash (Read/Write)
Configuration register is 0x2102
This output indicates that ubr920-k8v6y5-mz.122-5.bin
is the correct image. Refer to
(registered customers only)
to select and download the correct image for your cable modem.
IOS Software Upgrade Procedure for Cisco uBR9xx Cable Modems Using Console or
Telnet Access to upgrade the Cisco IOS Software on your cable modem. If
the cable modem is stuck in ROMmon, set the configuration register to
0x2102 and reload the router:
rommon 1 > confreg 0x2102
rommon 2 > reset
If the router remains in the ROMmon mode, the Cisco IOS Software image
is probably corrupt. Refer to the
Recovery for the Cisco 2500, 3000, AS5100, and uBR900 Series Routers for
Sometimes, the router gets stuck in Bootmode. In this case, the
Router_name(boot)> prompt appears. Check the
show version command output again and make sure that
the configuration register is 0x2102. If the configuration
register shows a different setting other than 0x2102, perform
Enter configuration commands, one per line. End with CNTL/Z.
System configuration has been modified. Save? [yes/no]: no
Proceed with reload? [confirm]
Note: You do not need to save the running configuration before the
If these configurations do not solve the problem, ensure that the RESET
switch is not stuck. If you are unsure whether or not the RESET switch is
stuck, power cycle the cable modem, and watch for these console
RESET SWITCH DETECTED
RESET SWITCH DETECTED - 10 seconds
RESET SWITCH DETECTED - 30 seconds
UBR924 platform with 16384 Kbytes of main memo
This message confirms that the RESET switch is stuck.
Perform these steps to help detect the problem if the cable modem boots
up but does not communicate with the headend:
Check the LED status on the cable modem (refer to the cable modem
troubleshooting documentation for information on LED status). For example, if a
Cisco uBR905 cable modem LINK LED blinks, the cable modem is locked to a signal
and connects to the headend per DOCSIS. If the LINK light continually blinks,
investigate further to determine where the cable modem fails.
Ask the service provider to run the show cable
modem command on the Cable Modem Termination System (CMTS) to
provide the status of the cable modem.
Refer to the
Flowchart to narrow down the problem and determine what you need to do
for the cable modem to achieve online status. Refer to
uBR Cable Modems Not Coming Online for more information.
If the cable modem is online but you are still unable to establish
connectivity with certain hosts at or beyond the Headend, check the CPE
configuration and IP connection. Refer to
Inability To Connect for more information.
If the cable modem displays an error message on the console, record the
error and check to see if the error is documented in the most common cable
modem error messages.
If you cannot connect to the cable modem through Telnet or the console
after the cable modem comes online, the cable modem functions normally, and
access to the cable modem is disabled. Refer to
or Telnet Access to Cable Modem Is Disabled. In order to rule out
hardware problems with the cable modem console connection, disconnect the
coaxial cable of the cable modem and then perform a power cycle. You must now
be able to connect to the cable modem through the console. If you are still
unsuccessful, make sure you use the right console cable. Refer to the