Troubleshooting guide

7-6
Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
OL-5169-01
Chapter 7 Troubleshooting the CMTS
Troubleshooting the Cisco uBR7246VXR
The Cisco uBR7246VXR software provides commands to help diagnose problems with:
• Media Terminal Adapters (MTAs) and the cable plant—Cisco uBR7246VXR software includes a
flap list that helps isolate problems between the cable plant (such as ingress noise or incorrect power
levels) and specific MTAs.
A “flap” is defined as an MTA being registered on the Cisco uBR7246VXR, de-registering, and then
immediately reregistering. With the flap list, you can quickly learn how to characterize trouble
patterns in the network, determine which amplifier or feeder line is faulty, distinguish an upstream
path problem from a downstream path problem, and isolate an ingress noise impairment from a plant
equipment problem.
Additional show commands are also available to help you diagnosis problems with cable modems.
• TCP/IP and provisioning problems—the system supports tracing and debugging DHCP related
messages on an administrator-specified uBR network interface, tracing and debugging all
MAC-layer DOCSIS messages for an administrator-defined MAC address, as well as other
debugging commands to monitor specific processes.
Troubleshooting the Cable Modem State
This section provides information on understanding the online state of the cable modem, and
troubleshooting problems indicated by this state, including RF problems.
Note Many but not all of the problems addressed in this section are RF-related. You should review this
section to generally understand troubleshooting the problems between the Cisco uBR7246VXR and
the MTAs in its domain.
The first and most useful command to use at the Cisco uBR7246VXR is show cable modem:
#show cable modem
The Online State field shows what status the MTA is in.
Table 7-1 displays the possible values for the state.
Interface Prim
Sid
Online
State
Timing
Offset
Rec
Power QoS CPE IP address MAC address
Cable2/0/U0 5 online(pt) 2290 -0.25 5 0 10.1.1.25 0050.7366.2223
Cable2/0/U0 6 offline 2287 -0.25 2 0 10.1.1.26 0050.7366.2221
Table 7-1 State Values
State Value Description
offline Cable modem considered offline
init (r1) Cable modem sent initial ranging
init (r2) Cable modem is ranging
init (rc) Cable modem ranging complete
init (d) Dhcp request received
init (i) Dhcp reply received; IP address assigned