Troubleshooting guide

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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
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Chapter 7 Troubleshooting the CMTS
Troubleshooting the Cisco uBR7246VXR
Note For underground HFC networks with 4 amplifier cascade length, a typical threshold value should be
3 dB. For overhead HFC networks with 4 amplifier cascade length, a typical threshold value should
be 4 dB. Longer coax cascades without return path thermal gain control and sites with extreme daily
temperatures will have larger threshold ranges.
The following example shows the power-adjust threshold being set to 5 dB:
router(config)# cable flap-list power-adjust threshold 5
Verifying Cable Flap List Power Adjustment Threshold
To verify the cable flap list power adjustment threshold, enter the following command, and note the
values in the P-Adj 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
Setting Cable Flap List Miss Threshold
You can specify the miss threshold for recording a flap-list event. A miss is the number of times a cable
modem does not acknowledge a MAC layer keepalive message from a cable modem card. An 8% miss
rate is normal for the Cisco cable modem cards. When the number of misses exceeds the threshold, the
cable modem is placed in the flap list.
Note A high miss rate can indicate intermittent upstream problems, fiber laser clipping, or common-path
distortion.
To set the miss threshold for recording a flap list event, use the cable flap-list miss-threshold command
in global configuration mode. To disable this function, use the no form of this command.
Command:
[no] cable flap-list miss-threshold misses
Syntax Description:
misses
Specifies the number of MAC-layer keepalive misses that results in the cable modems being placed
in the flap list. Valid values are 1 to 12.
No default behavior or values.
The following example shows how to set the miss threshold to 5:
router(config)# cable flap-list miss-threshold 5