Cisco cBR-8 Configuration And Troubleshooting Manual page 210

Information in the Flap List
timeout period. A pattern of misses can indicate a potential problem in either the downstream or upstream
path, or that a problem can be occurring in the registration process.
• Power Adjustments—DOCSIS cable modems can adjust their upstream transmission power levels to
adjust to unstable cable plant signal levels, up to a maximum allowable power level. Repeated power
adjustments usually indicate a problem with an amplifier in the upstream return path.
The flap-list feature is automatically enabled, but to use the flap list effectively, the cable system administrator
should also typically do the following:
• Set up a script to periodically poll the flap list, for example, every 15 minutes.
• Examine the resulting data and perform trend analysis to identify cable modems that are consistently in
the flap list.
• Query the billing and administrative database for cable modem MAC address-to-street address translation
and generate a report. The 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 indicate which
amplifier or feeder lines are faulty. The reports also help to quickly discern whether problems exist in
your downstream or upstream path and whether the problem is ingress noise or equipment related.
The flap list provides a quick way to quickly diagnose a number of possible problems. For example, if a
subscriber reports a problem, but the flap list for the cable interface that is providing services to them shows
little or no flap-list activity, the cable technician can assume that the Cisco CMTS and cable plant are
communicating reliably. The problem, therefore, is probably in the subscriber's computer equipment or in the
local connection to the cable modem.
Similarly, a cable technician can use the pattern of reinsertions, hits and misses, and power adjustments to
quickly troubleshoot the following types of problems:
• If a subscriber's cable modem shows a lot of flap-list activity, it is having some kind of communication
problem. Either the cable modem's hardware is faulty, its installation is faulty, the coaxial cable being
used is faulty, or some portion of the cable plant that services this cable modem is faulty.
• Focus on the top 10 percent of cable modems that are most active in the flap list, since these are the most
likely to indicate consistent and pervasive plant or equipment problems that will continue to disrupt
communication 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 problem with the provisioning
servers.
• Cable modems with high cyclic redundancy check (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.
In addition, the cable network administrators can use the flap list to collect quality control and upstream
performance data. Typically, the network operations center (NOC) saves the flap list to a database on a local
computer on a daily basis, providing the ability to generate reports that track upstream performance and
installation quality control, as well as to provide trend reports on cable plant problems.
Cisco cBR Series Converged Broadband Routers Troubleshooting and Network Management Configuration
Guide for Cisco IOS XE Fuji 16.8.x
198
Flap List Troubleshooting