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
Syntax Description:
mac-addr
(Optional) MAC address. Specify the 48-bit hardware address of an individual cable modem.
all
(Optional) Remove all cable modems from the flap-list table.
No default behavior or values.
Cable modems are removed from the flap list table after the number of days (between 1 and 60) specified
by the cable flap-list aging global configuration command. Use the clear cable flap-list command to
remove individual cable modems from the flap list while retaining flapping activity for other cable
modems, or to clear the entire flap list table.
The following example shows how to remove all the cable modems from the flap list table:
router# clear cable flap-list all
Performing Amplitude Averaging
The Cisco uBR7200 series 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 (flapping). To avoid
dropping flapping cable modems, the Cisco uBR7200 series universal broadband router averages a
configured number of RNG-REQ messages before it makes power adjustments. By compensating for a
potentially unstable return path, the Cisco uBR7200 series router 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 which paths the
Cisco uBR7200 series 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 Cable5/0/U1 0 2792 281 0 *45 58 Jul 27 16:54:50
0010.7bb3.fcfc Cable5/0/U1 0 19 4 0 !43 43 Jul 27 16:55:01
0010.7bb3.fcdd Cable5/0/U1 0 19 4 0 *3 3 Jul 27 16:55:01
The * symbol indicates that the CMTS is using the power adjustment method on this modem. The !
symbol indicates that the cable modem has reached maximum transmit power.
The following example shows the output of the show cable modem command:
router# show cable modem
Interface Prim Online Timing Rec QoS CPE IP address MAC address Sid
Cable3/0/U0 1 online 2257 0.00 3 0 10.30.128.142 0090.8330.0217
Cable3/0/U0 2 online 2262 *-0.50 3 0 10.30.128.145 0090.8330.020f
Cable3/0/U0 3 online 2260 0.25 3 0 10.30.128.146 0090.8330.0211
Cable3/0/U0 4 online 2256 *0.75 3 0 10.30.128.143 0090.8330.0216
Cable3/0/U0 5 online 2265 *0.50 3 0 10.30.128.140 0090.8330.0214
Cable3/0/U0 6 online 2256 0.00 3 0 10.30.128.141 0090.8330.0215
Cable3/0/U0 7 online 4138 !-1.00 3 1 10.30.128.182 0050.7366.124d
Cable3/0/U0 8 online 4142 !-3.25 3 1 10.30.128.164 0050.7366.1245
Cable3/0/U0 9 online 4141 !-3.00 3 1 10.30.128.185 0050.7366.17e3
Cable3/0/U0 10 online 4142 !-2.75 3 0 10.30.128.181 0050.7366.17ab
Cable3/0/U0 11 online 4142 !-3.25 3 1 10.30.128.169 0050.7366.17ef