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JUNOSg 3.0 G10 CMTS Hardware Guide
142
Flap List
The CMTS maintains a database of cable modems, along with various statistics for each cable
modem. When a cable modem exhibits behavior that matches pre-defined criteria—referred
to as a flap—an entry is added to a table called a flap list. Each flap list entry contains the
MAC address of the cable modem, along with additional modem statistics that can assist in
determining why the cable modem flapped. You can display the flap list by issuing the show
cable modem flaps command.
You can define global flap criteria or define flap criteria on an upstream interface basis. Flap
criteria defined for an upstream interface override those set at the global level. If a parameter
is not explicitly set, a flap is defined by its default value.
After an entry is added to the flap list for a cable modem, any subsequent flap for that cable
modem, whether defined explicitly or by default, updates that flap list entry with new
statistics (including a flap count). Examples of flaps include excessive initial ranging, missed
station maintenance opportunities, large upstream power adjustments, and an SNR dropping
below a threshold.
The flap list can be used to assist you with troubleshooting, locating CMTS and cable modem
configuration issues, and locating problems in the HFC plant without impacting throughput
and downstream performance, and without creating additional packet overhead throughout
the HFC network.
For more information about the flap list, see the JUNOSg Software Configuration Guide:
Interfaces, Cable, Policy, and Routing and Routing Protocols.
Use the Flap List for Troubleshooting
To display the flap list, issue the show cable flap-list command:
user@host> show cable flap-list
MAC-Address Interface Us/Port IM SM PAdj FAdj SNR MER
CER LTime LEvnt Total FAdjAmnt SNRavg MERavg CERavg
00:20:40:BF:5B:C4 ca-0/2/1 2/1 0 0 1 0 0 0
0 Feb 18 12:04:21 PADJ FLAP 1 0 33 23 0
00:E0:6F:03:16:DB ca-0/2/0 9/0 0 0 13 0 0 0
0 Feb 18 12:04:28 PADJ FLAP 13 0 28 24 0
Table 45 on page 143 provides potential HFC plant issues associated with some of the flaps
and statistics displayed in the output fields. The quantification of the flap counts and statistics
is plant dependent, so general qualifications, such as High and Low, are provided.