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ping docsis
If a CM responds to the ping docsis command, but does not respond to an IP ping, the problem could be
one of the following:
The CM is still in the registration process and has not yet come completely online. In particular, the
•
CM could be waiting for the DHCP server to assign it an IP address.
Severe interference or other faults on the physical layer (either the upstream or downstream).
•
Significant upstream signal error, distortion, or amplitude errors, often resulting in frequent power
•
adjustments (which are shown in the cable flap list).
A non-DOCSIS compliant upstream carrier-to-noise power ratio (C/N) that is between 14 and
•
21 dB, along with a mixed modulation profile, such as ranging request/response messages being sent
in QPSK mode and short and long data grants in 16-QAM mode.
The ping docsis command is a DOCSIS-compliant process that can be used with any two-way DOCSIS-
Note
compliant CM; the CM does not require any special features or code. The ping docsis command cannot
be used with telco-return CMs.
Table 2-23
Table 2-23 ping docsis Command Output Characters
Output Character Description
!
.
a
f
If a CM is already in the flap list, the ping docsis command increments the hit, miss, and power-
Note
adjustment fields for it in the cable flap list.
Cisco Broadband Cable Command Reference Guide
2-466
explains the different characters that can appear in the output for the ping docsis command:
Indicates that a successful response was received from the ping request. This
indicates that the CM is reachable from the CMTS and can respond to CMTS
requests at the DOCSIS MAC layer.
Indicates that a DOCSIS ping request was sent out but that the ping request timed
out without receiving a response. This indicates that the CM is having difficulties
maintaining DOCSIS MAC layer connectivity to the CMTS.
Note
If the ping docsis command displays a number of periods (.) along with
exclamation points (!), it strongly indicates the presence of RF noise or
physical cable and plant issues that is causing a loss of MAC layer
connectivity.
Indicates that a response was received but that an adjustment of frequency, power, or
timing was also made in the response. This indicates that, although the upstream
channel is functional, some sort of problem is forcing power averaging and other
misreads of the upstream received power signals.
Indicates that the CMTS failed to send the DOCSIS ping request because the CM is
offline, and therefore MAC-layer communication is not possible. This indicates that
the CM had previously registered with the CMTS, but that at some point it stopped
responding to the DOCSIS station maintenance messages and that the CMTS
eventually marked the CM as offline. The CM might have lost power or might have
been disconnected from the coaxial cable.
Tip
Use the
show cable modem
you used with the ping docsis command to show the current status of this
CM.
Chapter 2
Cisco CMTS Configuration Commands
command with the same MAC or IP address as
OL-1581-08
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