Troubleshooting guide

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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
OL-5169-01
Chapter 5 Troubleshooting DOCSIS Networks
Troubleshooting Slow Peformance
See the Cisco Cable Modem Termination System Command Reference for more information about
the show cable flap-list command.
• Cable modems displaying a * or a ! in the output of a show cable modem or show cable flap-list. A
* indicates a cable modem that is rapidly varying it's upstream power levels. This is indicative of a
poor connection to the cable plant, a faulty reverse path amplifier or rapidly changing cable plant
attenuation due to temperature or other environmental effects. A ! indicates a cable modem that has
reached it's maximum upstream power level. This is indicative of too much attenuation between the
cable modem and the CMTS, or a poor connection between the cable modem and the cable plant.
A sample output from the show cable modem command is shown below.
uBR7246-VXR# show cable modem
Interface Prim Online Timing Rec QoS CPE IP address MAC address
Sid State Offset Power
Cable3/0/U1 1 online 1549 !-1.00 5 0 10.1.1.10 005a.73f6.2213
Cable3/0/U0 2 online 1980 0.75 5 0 10.1.1.16 009b.96e7.3820
Cable3/0/U0 3 online 1981 *0.75 5 0 10.1.1.18 009c.96d7.3831
Cable3/0/U1 4 online 1924 0.25 5 0 10.1.1.24 000d.96c9.4441
Cable3/0/U1 5 online 1925 0.50 5 0 10.1.1.13 000e.96b9.4457
In the example seen above, the cable modem with MAC address 005a.73f6.2213 is transmitting at
its maximum output power. This would result in that modem not being able to transmit at the correct
level. Consequently this modem's upstream transmissions will not be heard as clearly as
transmissions from other modems. The cable modem with MAC address 009c.96d7.3831 has a
rapidly varying power output due to varying cable network attenuation.
See the Cisco Cable Modem Termination System Command Reference for more information about
the show cable modem and show cable flap-list commands.
More details about identifying and resolving RF noise issues can be found in Determining RF or
Configuration Issues On the CMTS and Connecting and Configuring the Cable Headend.
High CPU Utilization on the CMTS
In some circumstances a Cisco CMTS can become overloaded due to a sub-optimal configuration, over
utilization of certain management functions, or a very high number of packets being routed by the
CMTS.
The best way to determine the CPU utilization of a Cisco CMTS is to execute the show process cpu
command. The current CPU utilization is indicated on the first line of the output of the command.
In the lines of output shown below the first line, each process running on the CMTS is shown along with
the portion of the CPU being used by that process. This section of the show process cpu output is useful
for determining if one particular process or function is the cause of high CMTS CPU.
uBR7246-VXR# show process cpu
CPU utilization for five seconds: 45%/21%; one minute: 45%; five minutes: 31%
PID Runtime(ms) Invoked uSecs 5Sec 1Min 5Min TTY Process
1 12 9220 1 0.00% 0.00% 0.00% 0 Load Meter
2 69816 18276677 3 21.79% 22.10% 9.58% 2 Virtual Exec
3 36368 5556 6545 0.00% 0.06% 0.05% 0 Check heaps
4 0 1 0 0.00% 0.00% 0.00% 0 Chunk Manager
5 96 1436 66 0.00% 0.00% 0.00% 0 Pool Manager
6 0 2 0 0.00% 0.00% 0.00% 0 Timers
7 0 2 0 0.00% 0.00% 0.00% 0 Serial Backgroun
8 0 1 0 0.00% 0.00% 0.00% 0 CMTS ping
9 17020 101889 167 0.00% 0.00% 0.00% 0 EnvMon
10 0 1 0 0.00% 0.00% 0.00% 0 OIR Handler
. . . . . . .