Chapter 4 Troubleshooting the System
Troubleshooting Using Cable Flap Lists
list keeps track of the cable modem MAC address, up and down transitions, registration events, missed periodic ranging packets, upstream power adjustments and the physical interface on the
Cisco uBR7200 series.
Note Although this is a Cisco proprietary CMTS feature, it is compatible with all
The flap list collects the following station maintenance statistics:
•Detects interface up/down flap; the reinsertion counter counts the number of times a cable modem comes up and inserts into the network. This helps identify potential problems in the downstream because improperly provisioned cable modems tend to try to reestablish a link repeatedly.
•Detects intermittent upstream; the keepalive hits versus misses is the number of times cable modems don’t respond or don’t respond to the MAC layer keepalive messages. If there are a number of misses, this points to a potential problem in the upstream.
•Lists cable modem MAC addresses sorted by flap rate or most recent flap time.
•Shows power adjustment statistics during station maintenance polling; this represents the number of times the CMTS tells a cable modem to adjust the transmit power more than 3 dB. If constant power adjustments are detected, this usually indicates a problem with an amplifier. By looking at the cable modems in front and behind various amplifiers, you can find the source of failure.
The cable system administrator typically:
•Sets up a script to periodically poll the flap list, for example, every 15 minutes
•Uses the resulting data to perform trend analysis to identify the cable modems that are consistently in the flap list
•Queries the billing and administrative database for cable modem MAC
These reports can be given to the Customer Service Department or the cable plant’s Operations and Maintenance Department. Using these reports, maintenance personnel can quickly discern how characteristic patterns of flapping cable modems, street addresses, and flap statistics can indicate which amplifier or feeder lines are faulty. The reports also help you quickly discern whether problems exist in your downstream or upstream path, and whether the problem is ingress noise or equipment related.
Default values for the following
•cable
•cable
•cable
Note Since the cable flap list was originally developed, polling mechanisms have been enhanced since Cisco IOS Release 11.3.7 NA to have an increased rate of 1/sec when polls are missed. Cable modems go offline faster than the frequency hop period. This can cause the frequency to stay fixed while cable modems go offline. To compensate for this, as appropriate, you can reduce the hop period to 10 seconds.
Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide
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