Installation guide

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Cisco uBR7100 Series Universal Broadband Router Software Configuration Guide
OL-2238-03
Chapter 5 Troubleshooting the System
Troubleshooting Cable Flap Lists
completing registration. The upstream or downstream might not be stable enough for reliable link
establishment. Very low hits and miss counters and high insertion counters indicate provisioning
problems.
• Condition 3: Relatively high power adjustment counter.
Analysis: Indicates the power adjustment threshold is probably set at default value of 2 dB
adjustment. The modem transmitter step size is 1.5 dB, but the headend can command 0.25 dB step
sizes. Tuning your power threshold to 6 dB is recommended to decrease irrelevant entries in the flap
list. The power adjustment threshold can be set using cable flap power threshold <0-10 dB> from
the Cisco IOS global configuration mode.
A properly operating HFC network with short amplifier
cascades can use a 2 to 3 dB threshold.
• Condition 4: High P-Adj and CRC errors.
Analysis: This condition can indicate that the fiber node is clipping the upstream return laser.
Evaluate the modems with the highest CRC count first. If the modems are not going offline
(Ins = 0), this will not be noticed by subscribers. However, they could receive slower service due to
dropped IP packets in the upstream. This condition also results in input errors on the Cisco uBR7100
series router cable interface.
• Condition 5: High insertion rate.
Analysis: If link re-establishment happens too frequently, the modem is usually having a
registration problem. This is indicated by a high Ins counter which tracks the Flap counter.
Setting Cable Flap List Aging
You can specify the number of days to record and retain flapping activity on cable interfaces currently
in the flap list table. This value is known as the age of the flap list. The valid range is from 1 to 60 days.
To set the age of the cable flap list, use the following command in global configuration mode.
Verifying Cable Flap List Aging
To verify that cable flap list aging is set, enter the show cable flap list command:
CMTS01# show cable flap list
Mac Addr CableIF Ins Hit Miss CRC P-Adj Flap Time
0010.7b6b.5d1d C1/0 U0 0 688 169 0 0 3 Nov 5 12:28:50
0010.7b6b.5e15 C1/0 U0 1 707 185 0 0 5 Nov 5 12:29:52
0010.7b6b.5e27 C1/0 U0 1 707 198 0 0 5 Nov 5 12:29:55
0010.7b6b.5d29 C1/0 U0 1 709 205 0 0 5 Nov 5 12:29:52
0010.7b6b.5e2b C1/0 U0 1 710 204 0 0 7 Nov 5 12:30:16
Command Purpose
CMTS01(config)# cable flap-list aging days
Specifies the number of days to record and retain
flapping activity for the cable modems connected
to this Cisco uBR7100 series CMTS.