Troubleshooting guide

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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
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Chapter 7 Troubleshooting the CMTS
Troubleshooting the Cisco uBR7246VXR
Tips In Cisco IOS Release 12.0(7)XR2, Cisco IOS Release 12.1(1a)T1, and higher, the system supports
automatic power adjustments. The show cable flap-list and show cable modem commands now
indicate when the Cisco uBR7200 series has detected an unstable return path for a particular modem
and has compensated with a power adjustment. An asterisk (*) appears in the power adjustment field
for a cable modem when a power adjustment has been made; an exclamation point (!) appears when
the cable modem has reached its maximum power transmit level.
The following tips and scenarios allow you to use the flap list in the most effective way:
• If a subscriber's cable modem shows a lot of flap list activity, it is having communication problems.
• If a subscriber's cable modem shows little or no flap list activity, it is communicating reliably; the
problem is probably in the subscriber's computer equipment or in the connection to the cable
modem.
• The top 10% most active cable modems in the flap list are most likely to have difficulties
communicating with the headend.
• Cable modems with more than 50 power adjustments per day have a suspect upstream path.
• Cable modems with approximately the same number of hits and misses and with a lot of insertions
have a suspect downstream path (for example, low level into the cable modem).
• All cable modems incrementing the insertion at the same time indicates a provisioning server
failure.
• Cable modems with high CRC errors have bad upstream paths or in-home wiring problems.
• Correlating cable modems on the same physical upstream port with similar flap list statistics can
quickly resolve outside plant problems to a particular node or geography.
• Monitoring the flap list cannot affect cable modem communications.
• The flap list should be saved to a database computer and cleared at least once a day.
• Important upstream performance data can be obtained by tracking flap list trend data.
• Important installation quality control and performance data is directly available from the flap list.
Displaying the Flap List
The flap list can be queried using either the standard Simple Network Management (SNMP) API or the
CLI. Using any third party SNMP Management Information Base (MIB) browser, you can query the
ccsFlapTable in the CISCO-CABLE-SPECTRUM-MIB, a proprietary extension to the DOCSIS MIBs.
To display the cable flap list on a Cisco uBR7200 series cable router, use the show cable flap-list
command in privileged EXEC mode.
Command:
show cable flap-list [sort-flap | sort-time]
No default behavior or values.
Syntax Description:
sort-flap
(Optional) Sort by the number of times the cable modem has flapped.
sort-time
(Optional) Sort by the most recent time the cable modem is detected to have flapped.