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Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide
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Chapter4 Troubleshooting the System
Troubleshooting Using Cable Flap Lists
Tips InCisco IOS Release 12.0(7)XR2, Cisco IOS Release 12.1(1a)T1, and higher, the system
supportsautomatic power adjustments. The show cable flap-list and show cable modem
commands now indicate when the Cisco uBR7200 series router has detected an unstable
return path for a particular modem and has compensated with a power adjustment. An
asteriskappears in the poweradjustment field for a modem when a power adjustment has
been made; an exclamation point appears when the modem has reached its maximum
power transmit level and cannot increase its power level any further.
The following tips and scenarios allow you to use the flap list in the most effective way:
•Ifa subscriber's cable modemshows a lot of flap list activity, it is having communication problems.
•If a subscriber's cable modem showslittle 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 cablemodems 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 cablemodem).
•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 cablemodem 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.