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
You can view how severely the CMTS is rate limiting traffic to a particular cable modem by using the
show interface cable X/Y sid <Z> counters command, where cable X/Y is the cable interface which the
cable modem is connected to, and Z is the SID number of the modem being observed. This command
shows the number of times the CMTS has dropped a downstream packet or refused to allow an upstream
packet due to the modem exceeding its allowed throughput limits. If no value is specified for Z then
counter information for all cable modems connected to interface cable X/Y will be displayed.
uBR7246-VXR# show interface cable 3/0 sid 5 counters
Sid Inpackets Inoctets Outpackets Outoctets Ratelimit Ratelimit
BWReqDrop DSPktDrop
5 150927 9662206 126529 72008199 0 5681
The Ratelimit DSPktDrop field shows how many times the CMTS has dropped packets destined for the
cable modem due to the modem trying to exceed its allowed downstream throughput.
The Ratelimit BWReqDrop field shows how many times the CMTS has refused to let a cable modem
send a packet in the upstream path due to the modem trying to exceed its allowed upstream throughput.
In most circumstances this counter should always remain at 0. If it rises significantly above zero then it
may be that the cable modem being observed is not performing upstream rate limiting properly.
It should be noted that the values displayed by the show interface cable X/Y sid Z counters command
may be reset to zero by issuing the clear counters command as seen in the example below.
uBR7246-VXR# show interface cable 3/0 sid counters
Sid Inpackets Inoctets Outpackets Outoctets Ratelimit Ratelimit
BWReqDrop DSPktDrop
1 7 1834 7 1300 0 0
2 2052 549150 0 0 0 0
3 2 1244 2 708 0 0
4 2 1244 2 714 0 0
5 160158 10253220 134294 76423270 0 6023
6 2 1244 2 712 0 0
7 9 1906 4 858 0 0
9 6 1076 3 483 0 0
12 616 165424 0 0 0 0
uBR7246-VXR# clear counters
Clear "show interface" counters on all interfaces [confirm] <press enter here>
uBR7246-VXR# show interface cable 3/0 sid counters
Sid Inpackets Inoctets Outpackets Outoctets Ratelimit Ratelimit
BWReqDrop DSPktDrop
1 0 0 0 0 0 0
2 0 0 0 0 0 0
3 0 0 0 0 0 0
4 0 0 0 0 0 0
5 111 7104 92 52728 0 6
6 0 0 0 0 0 0
7 0 0 0 0 0 0
9 0 0 0 0 0 0
12 0 0 0 0 0 0
See the Cisco Cable Modem Termination System Command Reference for more information about the
show interface cable X/Y sid <Z> counters command.