C H A P T E R 4 Troubleshooting the System This chapter contains troubleshooting information.
Chapter 4 Troubleshooting the System Managing Cable Modems on the HFC Network Tips The SNR estimate for a cable modem installed at a headend should be between 35 dB and 39 dB. Although the exact value displayed will vary from cable modem to cable modem, values collected on the same cable modem from measurement to measurement will be consistent. Maximizing SNR optimizes cable modem reliability and service quality.
Chapter 4 Troubleshooting the System Managing Cable Modems on the HFC Network Verify Sync Message Interval To verify whether or not a sync message interval is configured, enter the show running-config command and look for the cable interface configuration information. If the sync message interval is deactivated or reset to its default value, the no sync interval command line appears in the output.
Chapter 4 Troubleshooting the System Managing Cable Modems on the HFC Network To activate cable modem upstream address verification, use the following cable interface configuration command. Table 4-3 Instructions to Activate Cable Modem Upstream Address Verification Command Purpose CMTS01(config-if)# cable source-verify [dhcp] Activate cable modem upstream verification. The dhcp option specifies that queries be sent to verify unknown IP addresses in upstream data packets.
Chapter 4 Troubleshooting the System Managing Cable Modems on the HFC Network Although the binary exponential backoff algorithm operates in a distributed fashion at different CMs, the CMTS provides centralized control for the backoff algorithm. To achieve this, it remotely monitors traffic load—the backlog developing on the contention channel—and then varies the backoff start and end specified in the MAPs for that upstream channel. This ensures colliding CMs are properly randomized in time.
Chapter 4 Troubleshooting the System Managing Cable Modems on the HFC Network Caution Only a trained CMTS administrator should adjust these values. To configure the dynamic map advance algorithm, use the following command in cable interface configuration mode.
Chapter 4 Troubleshooting the System Managing Cable Modems on the HFC Network To configure per modem filters, use the following commands in cable interface configuration mode. Table 4-6 Instructions to Configure Per Modem Filters Command Purpose CMTS01(config-if)# cable {modem | host | device} { | } access group Configure access lists to be specified on a per-interface and per-direction basis.
Chapter 4 Troubleshooting the System Managing Cable Modems on the HFC Network Configure the Maximum Number of Hosts Attached to a Cable Modem To specify the maximum number of hosts that can be attached to a subscriber’s cable modem, use the following command in cable interface configuration mode.
Chapter 4 Troubleshooting the System Managing Cable Modems on the HFC Network Table 4-9 Instructions to Clear Cable Modem Reset Command Purpose CMTS01(config-if)# clear cable modem mac-addr reset Remove the cable modem with a specific MAC address from the station maintenance list and reset it. CMTS01(config-if)# clear cable modem ip-addr reset Remove the cable modem with a specific IP address from the station maintenance list and reset it.
Chapter 4 Troubleshooting the System Managing Cable Modems on the HFC Network Verify Clear Cable Modem Counters To verify whether or not the counters in the Station Maintenance List are cleared, enter the following command. The station maintenance list counter will be 0. Configure Traffic Shaping Configure Downstream Rate Limiting and Shaping To configure downstream rate limiting or shape downstream traffic, use the following command in cable interface configuration mode.
Chapter 4 Troubleshooting the System Managing Cable Modems on the HFC Network To configure this, use the following command in cable interface configuration mode. Table 4-12 Instructions to Configure Upstream Shaping Command Purpose CMTS01(config-if)#[no] cable upstream rate-limit [token-bucket] Enables or disables DOCSIS rate limiting or shaping on an upstream channel. depends on the number of upstream channels on the specific cable modem card. Using Cisco IOS Release 12.
Chapter 4 Troubleshooting the System Managing Cable Modems on the HFC Network • Using time scheduled spectrum management, the upstream channel frequency reassignment process is initiated at a configured time of day or week. With combined blind and time scheduled strategies, blind hop tables are given time-variant configurability. The frequency or subband list can change with time. Blind frequency hop is performed within the spectrum specified to be currently available.
Chapter 4 Troubleshooting the System Managing Cable Modems on the HFC Network Sample output: noisy1#show cable spec Group Frequency Upstream No. Band Port (Mhz) 1 1 1 1 1 2 2 3 3 3 3 3 3 4 4 5 5 5 5 5 5 5 6 6 6 10.000- 0.000 11.000- 0.000 12.000- 0.000 13.000- 0.000 14.000- 0.000 10.000-15.000 10.208 [0.40] 20.000- 0.000 21.000- 0.000 22.000- 0.000 23.000- 0.000 24.000- 0.000 0.400 [0.80] 20.000-25.000 20.800 [1.60] 10.000- 0.000 11.000- 0.000 12.000- 0.000 13.000- 0.000 14.000- 0.000 13.000- 0.000 1.
Chapter 4 Troubleshooting the System Managing Cable Modems on the HFC Network Sample output: noisy1#show cable hop Upstream Port Port Status Cable3/0/U0 Cable3/0/U1 Cable3/0/U2 Cable3/0/U3 Cable3/0/U4 Cable3/0/U5 Cable4/0/U0 Cable6/0/U0 Poll Rate (ms) down 1000 admindown 1000 admindown 1000 admindown 1000 admindown 1000 admindown 1000 10.
Chapter 4 Troubleshooting the System Managing Cable Modems on the HFC Network Table 4-14 Show Cable Hop Parameter Descriptions Field Description Upstream Port The upstream port for this information line Port Status Show “down” if frequency is unassigned, “admindown” if the port is shutdown, or the center frequency of the channel if the port is up Poll Rate The rate station maintenance polls are generated (msec) Missed Poll Count The number of missing polls Min Poll Sample The number of polls
Chapter 4 Troubleshooting the System Polling Cable Modems Table 4-15 Upstream Port Parameter Descriptions (continued) Field Description Corr FEC Errors The number of correctable FEC errors on this upstream port Uncorr FEC Errors The number of uncorrectable FEC errors on this upstream port Sample output: noisy1#show cable hop Upstream Port Port Status Cable3/0/U0 Cable3/0/U1 Cable3/0/U2 Cable3/0/U3 Cable3/0/U4 Cable3/0/U5 Cable4/0/U0 Cable6/0/U0 Poll Rate (ms) down 1000 admindown 1000 admindown 1
Chapter 4 Troubleshooting the System Polling Cable Modems Enable SNMP Command Purpose Router(config)# snmp-server manager Opens the SNMP manager Router(config)# snmp-server community [Community String] [Permissions] Defines user permissions Configure Remote Modem Monitoring Command Purpose Router(config)# cable modem remote-query [polling interval] [Community string] Specifies how often SNMP polls the modem and allows you to configure access Verifying Remote Query Information To display informat
Chapter 4 Troubleshooting the System Understanding Show Command Responses Monitoring and Maintaining Remote Querying Use the following show commands to gather status information about the specified modems. Command Purpose Router# show cable flap-list Displays statistics on the quality of the modem connection. Router# show cable modem Displays statistics on modem states. Router# show cable modem remote-query Displays statistics gathered by SNMP agents on modem states.
Chapter 4 Troubleshooting the System Understanding Show Command Responses • The show cable flap-list and show cable modem commands now indicate when the Cisco uBR7200 series router has detected an unstable return path for a particular modem and has compensated with a power adjustment.
Chapter 4 Troubleshooting the System Understanding Show Command Responses See the sample command output below: router# show cable modem Interface Prim Online Sid State Cable3/0/U0 1 online Cable3/0/U0 2 online Cable3/0/U0 3 online Cable3/0/U0 4 online Cable3/0/U0 5 online Cable3/0/U0 6 online Cable3/0/U0 7 online Cable3/0/U0 8 online Cable3/0/U0 9 online Cable3/0/U0 10 online Cable3/0/U0 11 online Timing Rec Offset Power 2257 0.00 2262 *-0.50 2260 0.25 2256 *0.75 2265 *0.50 2256 0.00 4138 !-1.
Chapter 4 Troubleshooting the System Understanding Show Command Responses Note * means the noise power adjustment method is active for this modem; ! means the modem has reached its maximum transmit power • The QoS column contains the service class assigned to the modem • The CPE column identifies the number of devices behind the modem • The Max CPE column identifies the maximum number of devices configured for the modem • The IP address reveals the modem’s IP address • The MAC address reveals t
Chapter 4 Troubleshooting the System Understanding Show Command Responses See the following sample for detailed output of the show cable modem command: router#show Interface Cable3/0/U0 Cable3/0/U0 Cable3/0/U0 Cable3/0/U0 Cable3/0/U0 Cable3/0/U0 Cable3/0/U0 Cable3/0/U0 Cable3/0/U0 Cable3/0/U0 Cable3/0/U0 Cable3/0/U0 Cable3/0/U0 Cable3/0/U0 Cable3/0/U0 Cable4/0/U0 Cable4/0/U1 Cable4/0/U1 Cable4/0/U0 Cable4/0/U1 Cable4/0/U1 Cable4/0/U0 Cable4/0/U0 Cable4/0/U1 Cable4/0/U1 Cable4/0/U1 Cable4/0/U0 Cable4/0/U1
Chapter 4 Troubleshooting the System Understanding Show Command Responses See the following sample output of unregistered modems connected on upstream channel 0 for cable interface 3, port 0: router#show cable modem cable 3/0 upstream 0 unregistered Interface Prim Online Timing Rec QoS CPE IP address Sid State Offset Power Cable3/0/U0 1 offline 2264 -0.50 2 0 209.165.200.2 Cable3/0/U0 2 offline 4137 !-3.50 2 0 209.165.200.9 Cable3/0/U0 3 init(d) 4136 !-2.75 2 0 209.165.200.
Chapter 4 Troubleshooting the System Understanding Show Command Responses Following is a response to the show cable modem maintenance command using Cisco IOS Release 12.0(5)T1: uBR7200#show cable modem maintenance Interface SID MAC Address Cable4/0/U1 Cable4/0/U0 Cable4/0/U2 Cable4/0/U0 Cable4/0/U0 Cable4/0/U0 Cable4/0/U2 Cable4/0/U1 Cable4/0/U2 Cable4/0/U1 Cable4/0/U1 Cable4/0/U1 Cable4/0/U1 Cable4/0/U2 Cable4/0/U1 1 2 11 13 16 20 24 27 28 30 31 32 33 35 36 0010.7b6b.5e27 0010.7b6b.5e15 0050.731c.
Chapter 4 Troubleshooting the System Understanding Show Command Responses Table 4-16 Show Interface Cable Command Field Descriptions Field Description Cable slot/port is up/...administratively down Indicates whether the interface hardware is currently active or taken down by the administrator line protocol is up/...
Chapter 4 Troubleshooting the System Understanding Show Command Responses Table 4-16 Show Interface Cable Command Field Descriptions (continued) Field Description drops Indicates the number of packets dropped due to a full queue Five minute input rate Five minute output rate Average number of bits and packets transmitted per second in the last five minutes packets input Total number of error-free packets received by the system bytes input Total number of bytes, including data and MAC encapsula
Chapter 4 Troubleshooting the System Understanding Show Command Responses Table 4-16 Show Interface Cable Command Field Descriptions (continued) Field Description output buffer failures Number of times the output buffer has failed output buffer swapped out Number of times the output buffer has been swapped out See the following sample output for the downstream cable interface of slot 6 on port 0 from the show interface cable downstream command: router# show interface cable 6/0 downstream Cable6/0:
Chapter 4 Troubleshooting the System Understanding Show Command Responses Table 4-18 Show Interface Cable Upstream Command Field Descriptions Field Description Cable Indicates the location of the upstream interface Upstream is up/...
Chapter 4 Troubleshooting the System Understanding Show Command Responses Table 4-18 Show Interface Cable Upstream Command Field Descriptions (continued) Field Description CIR admission control (formerly: Current Admission Control Status) Indicates the status of admission control on the upstream channel ENFORCED status allows users to enable admission control on a per port basis. This controls how limited bandwidth is allocated. NOT ENFORCED status indicates that there is no admission control.
Chapter 4 Troubleshooting the System Understanding Show Command Responses Table 4-18 Show Interface Cable Upstream Command Field Descriptions (continued) Field Description Avg percent minislots lost on late MAPs Indicates on average what percent of slots are lost because a MAP interrupt was too late Current minislot count (formerly: Last Minislot Stamp (current_time_base)) Indicates the current minislot count at the CMTS. FLAG indicates the timebase reference.
Chapter 4 Troubleshooting the System Understanding Show Command Responses • Counters for each type of upstream slot scheduled in the MAPs for this upstream channel---The “Init Mtn IEs 800” means that the MAC scheduler has added 800 initial maintenance information elements (slots) at the time the show command was issued. • MAC scheduling statistics to display what percentage of the upstream bandwidth is utilized for each type of slot on an average.
Chapter 4 Troubleshooting the System Understanding Show Command Responses See the following display output for the verbose keyword extension for all SIDs on the specified interface: router# show interface c3/0 sid counters verbose Sid : 1 Input packets : 39 Input octets : 15964 Output packets : 30 Output octets : 8796 BW requests received : 40 Grants issued : 40 Rate exceeded BW request drops : 0 Rate exceeded DS packet drops : 0 Sid : 2 Input packets : 0 Input octets : 0 Output packets : 0 Output octets
Chapter 4 Troubleshooting the System Understanding Show Command Responses See the following display for the counters of the SIDs connected to the specified interface: router# show interface c3/0 sid counters Sid Inpackets Inoctets Outpackets Outoctets 1 2 3 40 0 0 16586 0 0 31 0 0 9160 0 0 Ratelimit BWReqDrop 0 0 0 Ratelimit DSPktDrop 0 0 0 See the following display for the counters of SID 1 on the specified interface: router# show interface c3/0 sid 1 counters Sid Inpackets Inoctets Outpackets Out
Chapter 4 Troubleshooting the System Troubleshooting Using Cable Flap Lists Table 4-19 show interface cable sid Command Field Descriptions (continued) Field Description Rate exceeded DS packet drops Number of downstream packets lost by this SID Ratelimit BWReqDrop Number of bandwidth requests not granted by this SID Ratelimit DSPktDrop Number of downstream packets lost by this SID 1st time online Time at which the modem with this SID connected Times online Number of times the modem with this
Chapter 4 Troubleshooting the System Troubleshooting Using Cable Flap Lists list keeps track of the cable modem MAC address, up and down transitions, registration events, missed periodic ranging packets, upstream power adjustments and the physical interface on the Cisco uBR7200 series. Note Although this is a Cisco proprietary CMTS feature, it is compatible with all DOCSIS-compliant cable modems. Unlike SNMP, the flap list uses zero bandwidth.
Chapter 4 Troubleshooting the System Troubleshooting Using Cable Flap Lists Tips In Cisco IOS Release 12.0(7)XR2, Cisco IOS Release 12.1(1a)T1, and higher, the system supports automatic power adjustments. The show cable flap-list and show cable modem commands now indicate when the Cisco uBR7200 series router has detected an unstable return path for a particular modem and has compensated with a power adjustment.
Chapter 4 Troubleshooting the System Troubleshooting Using Cable Flap Lists Following is a sample response to the show cable flap command: uBR7200#show cable flap Mac Addr 0010.9500.461f 0010.9500.446e 0010.9500.38ec 0010.9500.4474 0010.9500.4672 0010.9500.38f0 0010.9500.e8cb 0010.9500.38f6 0010.9500.4671 0010.9500.38eb 0010.9500.3ce2 0010.9500.e8d0 0010.9500.4674 0010.9500.4677 0010.9500.4614 0010.9500.3be9 0010.9500.4609 0010.9500.3cb8 0010.9500.460d 0010.9500.3cba 0010.9500.3cb4 0010.9500.
Chapter 4 Troubleshooting the System Troubleshooting Using Cable Flap Lists Table 4-20 Flap List Statistics Description Statistic Description MAC ID This is the MAC-layer address of a cable modem. The first six digits indicate the vendor ID of the cable modem manufacturer, followed by six digits indicating a unique host address. Each cable modem's MAC address is unique. Cable IF This is the physical upstream interface on the Cisco uBR7200.
Chapter 4 Troubleshooting the System Troubleshooting Using Cable Flap Lists Table 4-20 Flap List Statistics Description Hit and Miss The HIT and MISS columns are keepalive polling statistics between the Cisco uBR7200 series and the cable modem. The station maintenance process occurs for every modem approximately every 25 seconds. When the CMTS receives a response from the modem, the event is counted as a Hit. If the CMTS does not receive a response from the cable modem, the event is counted as a Miss.
Chapter 4 Troubleshooting the System Troubleshooting Using Cable Flap Lists Table 4-20 Flap Flap List Statistics Description The Flap counter indicates the number of times the modem has flapped. This counter is incremented when one of the following events is detected: Unusual modem insertion or reregistration attempts.
Chapter 4 Troubleshooting the System Troubleshooting Using Cable Flap Lists Set Cable Flap List Aging You can specify the number of days to record and retain flapping activity on cable modems currently in the flap-list table. This value is known as the age of the flap list. The valid range is from 1 to 60 days. To set the age of the flap list, use the following command in global configuration mode.
Chapter 4 Troubleshooting the System Troubleshooting Using Cable Flap Lists Set Cable Flap List Power Adjustment Threshold You can specify the power adjustment threshold that will cause a flap-list event to be recorded. When the power adjustment of a cable modem meets or exceeds the threshold, the cable modem is placed in the flap list. The valid range is from 1 to 10 dBmV. Note A power adjustment threshold of less than 2 dBmV might cause excessive flap list event recording.
Chapter 4 Troubleshooting the System Troubleshooting Using Cable Flap Lists Verify Cable Flap List Miss Threshold To verify the cable flap list miss threshold, enter the show cable flap list command: CMTS01# show cable flap list Mac Addr CableIF Ins 0010.7b6b.5d1d C3/0 U0 0 0010.7b6b.5e15 C3/0 U0 1 0010.7b6b.5e27 C3/0 U0 1 0010.7b6b.5d29 C3/0 U0 1 0010.7b6b.
Chapter 4 Troubleshooting the System Troubleshooting Using Cable Flap Lists Customize Other Flap List Values and Related Commands The following displays flap list with different sorting options: show cable modem flap-list [cable | sort-flap | sort-time | sort-interface] The following sets the threshold value for link establishment: [no] cable flap-list insertion-time Note A modem is tagged as flapping if the insertion time exceeds this value.
Chapter 4 Troubleshooting the System Performing Amplitude Averaging 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—known as flapping. To avoid dropping flapping cable modems, the Cisco uBR7200 series universal broadband router averages a configurable number of RNG-REQ messages before it makes power adjustments.
Chapter 4 Troubleshooting the System Performing Amplitude Averaging Table 4-27 Note Caution Note Cable Upstream Power Adjust Syntax Descriptions Syntax Valid Values n Specifies the upstream port number. threshold # Specifies the power adjustment threshold. The threshold range is from 0 through 10 dB. The default is 1 dB. tolerable value Determines if the status of the RNG-RSP should be set to CONTINUE or SUCCESS. The range is from 2 through 15 dB. The default is 2 dB.
Chapter 4 Troubleshooting the System Setting Downstream Test Signals Table 4-28 Cable Upstream Freq-adj Averaging Syntax Descriptions Syntax Valid Values n Specifies the upstream port number. averaging Specifies that a percentage of frequency adjustment packets is required to change the adjustment method from the regular power adjustment method to the noise power adjustment method.
Chapter 4 Troubleshooting the System Pinging Unresponsive Cable Modems Configure PRBS Test Signals Table 4-30 Instructions to Configure PRBS Test Signals Step Command Purpose 1. # router(config-if)# cable downstream if-output prbs Generates a PRBS test signal on the downstream channel. The interface is shut down. 2. Router(config-if)# no cable downstream if-output Stops sending test signals. Note Remember to reenable the interface to resume normal operations.
Chapter 4 Troubleshooting the System Using Cable Interface Debug Commands Verify the Ping The ping docsis command returns a verification from a cable modem that is pinged: Queueing 5 MAC-layer station maintenance intervals, timeout is 25 msec: !!!!! Success rate is 100 percent (5/5) Tips If you are having trouble, make sure you are using a valid MAC or IP address for the cable modem you want to ping.
Chapter 4 Troubleshooting the System Using Cable Interface Debug Commands Debug Environmental Monitor Messages This command activates debugging of the Cisco uBR7200 series environmental monitor. When this command is activated, all environmental monitor messages are displayed on the Cisco uBR7200 series console.
Chapter 4 Troubleshooting the System Using Cable Interface Debug Commands To deactivate debugging of cable MAC messages, use the following command: CMTS01# no debug cable mac-messages Debug Cable Maps This command activates debugging of cable maps that identify data on cable interfaces. When this command is activated, messages related to cable maps are displayed on the Cisco uBR7200 series console.
Chapter 4 Troubleshooting the System Using Cable Interface Debug Commands Debug Cable Modem Ranging Messages This command activates debugging of ranging messages from cable modems on the HFC network. When this command is activated, ranging messages generated when cable modems request or change their upstream frequencies are displayed on the Cisco uBR7200 series console.
Chapter 4 Troubleshooting the System Using Cable Interface Debug Commands Debug Spectrum Management This command activates debugging of spectrum management (frequency agility) on the HFC network. When this command is activated, messages generated because of spectrum group activity are displayed on the Cisco uBR7200 series console. Spectrum group activity can be additions or changes to spectrum groups, or frequency and power level changes controlled by spectrum groups.
Chapter 4 Troubleshooting the System Managing the Cisco uBR7246 VXR Clock Card Debug Upstream Channel Description (UCD) Messages This command activates debugging of upstream channel descriptor (UCD) messages. UCD messages contain information about upstream channel characteristics and are sent to the cable modems on the HFC network. Cable modems that are configured to use enhanced upstream channels use these UCD messages to identify and select an enhanced upstream channel to use.
Chapter 4 Troubleshooting the System Managing the Cisco uBR7246 VXR Clock Card Force Alternate Clock To select the external timing source when the clock card is in holdover mode, use the cable clock force global configuration command. To disable the selection and return to the default, use the no form of this command. cable clock force {primary | secondary} no cable clock force Setting the cable clock to primary forces the primary source to act as the clock reference.
Chapter 4 Troubleshooting the System Managing the Cisco uBR7246 VXR Clock Card The following sample output from the show cable clock command shows both external sources are available and the clock card is providing the clock reference: Router# show cable clock Clockcard primary input is present Clockcard secondary input is present Cable clock reference is clockcard primary input Cable3/0 Timestamp clock reference is from Clockcard Cable4/0 Timestamp clock reference is from Clockcard Show Clock Hardware
Chapter 4 Troubleshooting the System Managing the Cisco uBR7246 VXR Clock Card The following is sample output from the show diag command displaying diagnostic information for the cable clock card: router# show diag Clockcard: National clock card with T1 controller EEPROM contents at hardware discovery: Hardware Revision :1.
Chapter 4 Troubleshooting the System Managing the Cisco uBR7246 VXR Clock Card Show Clock Frames To display information about the midplane TDM clock reference, use the show frame-clocks privileged EXEC command.