Troubleshooting guide

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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
OL-5169-01
Chapter 7 Troubleshooting the CMTS
Troubleshooting the Cisco uBR7246VXR
• Condition 3: Relatively high power adjustment counter.
Analysis: Indicates the power adjustment threshold is probably set at default value of 2 dB
adjustment. the cable modem transmitter step size is 1.5 dB, whereas the headend may 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 may 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 2-3 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 cable modems with the highest CRC count first. If the cable modems are not going
offline (Ins = 0), this will not be noticed by the subscriber. However, they could receive slower
service due to dropped IP packets in the upstream. This condition will also result in input errors on
the Cisco uBR7200 series cable interface.
• Condition 5: High insertion rate.
Analysis: If link re-establishment happens too frequently, then the cable modem is usually having
a registration problem.This is indicated by a high Ins counter which tracks the Flap counter.
Configuring Flap List Parameters
You can set certain flap list parameters by using the commands described in the following sections.
Setting Cable Flap List Aging
To specify the number of days to keep a cable modem in the flap-list table before aging it out of the table,
use the cable flap-list aging command in global configuration mode. To disable this feature, use the no
form of this command.
Command:
[no] cable flap-list aging number-of-days
Syntax Description:
number-of-days
Specifies how many days of cable modem performance is retained in the flap list. Valid values are
from 1 to 60 days.
No default behavior or values.
The following example shows how to specify that the flap-list table retain two days of performance for
this cable modem:
router(config)# cable flap-list aging 2
Verifying Cable Flap List Aging
To verify that cable flap list aging is set, enter the following command and note the dates in the Time
column:
show cable flap list
Mac Addr CableIF Ins Hit Miss CRC P-Adj Flap Time
0010.7b6b.5d1d C3/0 U0 0 688 169 0 0 3 Nov 5 12:28:50
0010.7b6b.5e15 C3/0 U0 1 707 185 0 0 5 Nov 5 12:29:52
0010.7b6b.5e27 C3/0 U0 1 707 198 0 0 5 Nov 5 12:29:55
0010.7b6b.5d29 C3/0 U0 1 709 205 0 0 5 Nov 5 12:29:52
0010.7b6b.5e2b C3/0 U0 1 710 204 0 0 7 Nov 5 12:30:16