Cisco cBR 8 User Manual

decrease irrelevant entries in the flap list. The power-adjustment threshold can be set using cable flap
power threshold <0-10 dB> in 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 is not 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
CMTS router cable interface.
•
Condition 5: High insertion rate. Analysis: If link reestablishment happens too frequently, the modem
is usually having a registration problem. This is indicated by a high Ins counter, which tracks the Flap
counter.
Performing Amplitude Averaging
The CMTS uses an averaging algorithm to determine the optimum power level for a cable modem with low
carrier-to-noise ratio that is making excessive power adjustments—known as flapping. To avoid dropping
flapping cable modems, the CMTS averages a configurable number of RNG-REQ messages before it makes
power adjustments. By compensating for a potentially unstable return path, the CMTS maintains connectivity
with affected cable modems. You can interpret these power adjustments, however, as indicating unstable
return path connections.
The show cable flap-list and show cable modem commands are expanded to indicate to which paths the
CMTS is making power adjustments and which modems have reached maximum transmit power settings.
These conditions indicate unstable paths that should be serviced.
The following example shows the output of the show cable flap-list command:
Router# show cable flap-list
MAC Address Upstream Ins Hit Miss CRC P-Adj Flap Time
0010.7bb3.fd19 Cable1/0/U1 0 2792 281 0 *45 58 Jul 27 16:54:50
0010.7bb3.fcfc Cable1/0/U1 0 19 4 0 !43 43 Jul 27 16:55:01
0010.7bb3.fcdd Cable1/0/U1 0 19 4 0 *3 3 Jul 27 16:55:01
The asterisk (*) indicates that the CMTS is using the power-adjustment method on this modem. An exclamation
point (!) indicates that the modem has reached maximum transmit power.
Output of the show cable modem command appears below:
Router# show cable modem
Interface Prim Online Timing Rec QoS CPE IP address MAC address
Sid State Offset Power
Cable1/0/U0 1 online 2257 0.00 3 0 10.30.128.142 0090.8330.0217
Cable1/0/U0 2 online 2262 *-0.50 3 0 10.30.128.145 0090.8330.020f
Cable1/0/U0 3 online 2260 0.25 3 0 10.30.128.146 0090.8330.0211
Cable1/0/U0 4 online 2256 *0.75 3 0 10.30.128.143 0090.8330.0216
Cable1/0/U0 5 online 2265 *0.50 3 0 10.30.128.140 0090.8330.0214
Cable1/0/U0 6 online 2256 0.00 3 0 10.30.128.141 0090.8330.0215
Cable1/0/U0 7 online 4138 !-1.00 3 1 10.30.128.182 0050.7366.124d
Cable1/0/U0 8 online 4142 !-3.25 3 1 10.30.128.164 0050.7366.1245
Cable1/0/U0 9 online 4141 !-3.00 3 1 10.30.128.185 0050.7366.17e3
Cable1/0/U0 10 online 4142 !-2.75 3 0 10.30.128.181 0050.7366.17ab
Cable1/0/U0 11 online 4142 !-3.25 3 1 10.30.128.169 0050.7366.17ef
Similar to the show cable flap-list command display, the * symbol in the show cable modem command
output indicates that the CMTS is using the power-adjustment method on this CM. The ! symbol indicates
that the CM has reached maximum transmit power.
Cisco cBR Series Converged Broadband Routers Troubleshooting and Network Management Configuration Guide
for Cisco IOS XE Fuji 16.8.x
211
Flap List Troubleshooting
Troubleshooting Suggestions

Cisco cBR 8 Specifications

General

Brand	Cisco
Model	cBR 8
Category	Network Router
Language	English