Table Of Contents
Troubleshooting
Before Contacting Cisco or Your Reseller
ADSL Troubleshooting
ADSL Cable Requirements
G.SHDSL Troubleshooting
show dsl interface Command
ATM Troubleshooting Commands
ping atm interface Command
show interface Command
debug atm Commands
Before Using Debug Commands
debug atm errors Command
debug atm events Command
debug atm packet Command
Troubleshooting Telephone Interfaces
Troubleshooting Serial Line Problems
Synchronous CSU/DSU Clocking Problems
Detecting Problems
Performing Ping Tests
Performing Loopback Tests
Local Loopback Tests
Remote Loopback Tests
Synchronous Leased Line Problems
Asynchronous Dial-Up Problems
Troubleshooting Problems with Modem and Router Connection
No Connectivity Between Modem and Router
Modem Does Not Dial
Modem Does Not Answer
Modem Hangs Up Shortly After Connecting
Dial-Up Client Receives No EXEC Prompt
Dial-Up Session Sees Garbage
Dial-Up Session Ends Up in Existing Session
Modem Cannot Send or Receive Data
Modem Cannot Send or Receive IP Data
Modem Does Not Disconnect Properly
Link Deactivates Too Quickly
Link Does Not Deactivate or Stays Activated Too Long
Poor Dial-Up Connection Performance
Frame Relay Problems
Frame Relay Link Is Down
Cannot Ping Remote Router
Cannot Ping End to End
X.25 Problems
No Connections over X.25 Link
Excess Serial Errors on X.25 Link
Software Upgrade Methods
Recovering a Lost Password
Changing the Configuration Register
Resetting the Router
Resetting the Password and Saving Your Changes
Resetting the Configuration Register Value
Managing the Cisco Router Web Setup Tool
Pointers to CRWS Documentation
Troubleshooting
Use the information in this chapter to help isolate problems you might encounter with Cisco 800 series and Cisco SOHO series routers or to rule out the router as the source of the problem. This chapter contains the following sections:
•
Before Contacting Cisco or Your Reseller
•ADSL Troubleshooting
•G.SHDSL Troubleshooting
•ATM Troubleshooting Commands
•Troubleshooting Telephone Interfaces
•Troubleshooting Serial Line Problems
•Software Upgrade Methods
•Recovering a Lost Password
•Managing the Cisco Router Web Setup Tool
Before troubleshooting a software problem, you must connect a terminal or PC to the router via the light-blue console port. (For information on making this connection, see the documentation listing in the "Related Documents" section on page xxxi.) With a connected terminal or PC, you can read status messages from the router and enter commands to troubleshoot a problem.
You can also remotely access the interface (Ethernet, ADSL, or telephone) by using Telnet. The Telnet option assumes that the interface is up and running.
Before Contacting Cisco or Your Reseller
If you cannot locate the source of a problem, contact your local reseller for advice. Before you call, you should have the following information ready:
•Chassis type and serial number
•Maintenance agreement or warranty information
•Type of software and version number
•Date you received the hardware
•Brief description of the problem
•Brief description of the steps you have taken to isolate the problem
ADSL Troubleshooting
This section describes some asymmetric digital service line (ADSL) troubleshooting checks that you can perform if the router is not working properly. If you experience trouble with the ADSL connection, make sure to verify the following:
•That the ADSL line is connected and is using pins 3 and 4. For more information on the ADSL connection, refer to the hardware guide for your router.
•That the ADSL CD LED is on. If it is not on, the router may not be connected to the digital subscriber line access multiplexer (DSLAM). For more information on the ADSL LEDs, refer to the hardware installation guide specific to your router.
•That you are using the correct Asynchronous Transfer Mode (ATM) variable path indentifier/variable circuit identifier (VPI/VCI).
•That the DSLAM supports discrete multi-tone (DMT) Issue 2.
ADSL Cable Requirements
The ADSL cable that you connect to the Cisco router must be 10BASE-T Category 5, unshielded twisted-pair (UTP) cable. Using regular telephone cable can introduce line errors.
G.SHDSL Troubleshooting
Symmetrical high-data-rate digital subscriber line (G.SHDSL) is available on Cisco 828 and Cisco SOHO 78 routers. This section describes some G.SHDSL troubleshooting checks that you can perform if the router is not working properly. If you experience trouble with the G.SHDSL connection, verify the following:
•That the G.SHDSL line is connected and is using pins 3 and 4. For more information on the G.SHDSL connection, refer to the Cisco 828 Router and SOHO 78 Router Hardware Installation Guide.
•That the G.SHDSL CD LED is on. If it is not on, the router may not be connected to the DSLAM. For more information on the G.SHDSL LEDs, refer to the Cisco 828 Router and SOHO 78 Router Hardware Installation Guide.
•That you are using the correct ATM VPI/VCI.
•That the DSLAM supports G.SHDSL.
show dsl interface Command
Use the show dsl interface command to display the status of a G.SHDSL physical port on the router.
The following is an example of output for the show dsl interface command:
_Router# show dsl interface atm0
Globespan G.SHDSL/SDSL Chipset Information
Equipment Type: Customer Premise
Operating Mode: G.SHDSL Annex A
Clock Rate Mode: Fixed rate Mode
Loop Attenuation: 0.4294963186 dB
Receiver Gain: 4.2040 dB (2271, 4210, 90)
Last Activation Status: No Failure (0x0)
Provider Code: 0x4E505347
Vendor Data: 0x0 0x0 0x0 0x0
Performance statistics since reload:
Number of LOS failures: 0
Number of LOSQ failures: 0
Number of coding violations: 0
Number of errored seconds: 0
Number of severely errored seconds: 0
Number of unavailable seconds: 0
Performance statistics for: Current 15 mins Current 24
Hours
Time elapsed since beginning of interval: 6Min 0Hr
6Min
Number of LOS seconds: 0 0
Number of LOSQ seconds: 0 0
Number of code violations: 0 0
Number of errored seconds: 0 0
Number of severely errored seconds: 0 0
Number of unavailable seconds: 0 0
Table 9-1 describes possible command output for the show dsl interface command. Each line in the command output example corresponds to a row in this table.
Table 9-1 show dsl interface Command Output Description
Output
|
Description
|
Equipment Type
|
•Customer premises equipment (CPE), if connected to a DSLAM.
•Central offices (COs); if the routers are connected back to back, then one of the routers can act as a CO.
|
Operating Mode
|
G.SHDSL annex configuration
|
Clock Rate Mode
|
Upstream and downstream bit rate configuration. Either AUTO for fixed.
|
Reset Count
|
Number of times the G.SHDSL chip has been reset since power-up.
|
Requested rate
|
User-specified bit rate requirement.
|
Actual rate
|
The actual bit rate that the transceiver is using.
|
Modem Status
|
•Handshake, when local transceiver tries to reach the far-end transceiver.
•Training; indicates that the startup training is in progress.
•Data, if successfully trained.
|
Received SNR
|
The received signal-to-noise ratio (SNR).
|
Loop Attenuation
|
The difference in decibels (dB) between the power received at the near-end and the power transmitted from the far-end.
|
Transmit Power
|
Local symmetric digital subscriber line transmission unit (STU) transmit power.
|
Receiver Gain
|
Total receiver gain.
|
Last Activation Status
|
Defines the last failure state of the G.SHDSL chip.
|
CRC Errors
|
Cyclic redundancy check (CRC) errors.
|
Chipset Version
|
Vendor's chipset information.
|
Firmware Version
|
Vendor's firmware release version.
|
Country Code
|
The country identification for the far end.
|
Provider Code
|
Identification of the vendor.
|
Vendor data
|
Vendor-specific information.
|
Number of LOS failures
|
Loss of synchronization counter increased when it contains one or more error in the framing bits. If the counter continues to increase during or after training, the line might be noisy or the cable is not connected.
|
Number of LOSQ failures
|
Loss of signal quality counter is increased when SNR is below the threshold.
|
Number of code violations
|
Code violation is defined as a count of the CRC anomalies occurring during the accumulation period.
|
Number of errored seconds
|
An errored second is a count of 1-second intervals during which one or more CRC anomalies/loss of sync words are declared.
|
Number of severely errored seconds
|
A severely errored second is a count of 1-second intervals during which 50 or more CRC anomalies are declared.
|
Number of unavailable seconds
|
An unavailable second is a count of 1-second intervals for which the DSL line is unavailable.
|
ATM Troubleshooting Commands
This section describes some ATM troubleshooting commands.
ping atm interface Command
You can use the ping atm interface command to determine if a particular PVC is in use. The PVC does not need to be configured on the router in order for you to use this command.
For example, to test whether PVC 1/200 is in use, use the following command:
Router# ping atm interface atm 0 1 200 seg-loopback
Type escape sequence to abort.
Sending 5, 53-byte segment OAM echoes, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max =
148/148/148 ms
This command sends five OAM F5 loopback packets to the DSLAM (segment OAM packets). If the PVC is configured at the DSLAM, the ping is successful.
To test whether the PVC is being used at the aggregator, enter the following command:
Router# ping atm interface atm 0 1 200 end-loopback
Type escape sequence to abort.
Sending 5, 53-byte end-to-end OAM echoes, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max =
400/401/404 ms
This command sends end-to-end OAM F5 packets, which are echoed back by the aggregator.
show interface Command
Use the show interface command to display the status of all physical ports (Ethernet and ATM) and logical interfaces on the router. Significant messages in the command output are shown in bold. Significant messages are described in Table 9-2.
ATM0 is up, line protocol is up
Hardware is PQUICC_SAR (with Alcatel ADSL Module)
Internet address is 14.0.0.16/8
MTU 1500 bytes, sub MTU 1500, BW 640 Kbit, DLY 80 usec,
reliability 40/255, txload 1/255, rxload 1/255
Encapsulation ATM, loopback not set
Encapsulation(s):AAL5, PVC mode
10 maximum active VCs, 1 current VCCs
VC idle disconnect time:300 seconds
Last input 01:16:31, output 01:16:31, output hang never
Last clearing of "show interface" counters never
Input queue:0/75/0 (size/max/drops); Total output drops:0
Queueing strategy:Per VC Queueing
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
512 packets input, 59780 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 1024 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
426 packets output, 46282 bytes, 0 underruns
0 output errors, 0 collisions, 2 interface resets
0 output buffer failures, 0 output buffers swapped out
Ethernet0 is up, line protocol is up
Hardware is PQUICC Ethernet, address is 0000.Oc13.a4db
Internet address is 170.1.4.101/24
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
reliability 255/255., txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Dialer 1 is up, line protocol is up
Hardware is Dialer interface
Internet address is 1.1.1.1/24
MTU 1500 bytes, BW 100000 Kbit, DLY 100000 usec, reliability
255/255. txload 1/255, rxload 1/255
Encapsulation PPP, loopback not set
DTR is pulsed for 5 seconds on reset
Table 9-2 describes possible command output for the show interface command. Each line in the command output example corresponds to a row in this table.
Table 9-2 show interface Command Output Description
Output
|
Description
|
ATM0 is up, line protocol is up
Other possible messages:
ATM0 is down, line protocol is down
ATM0 is down, line protocol is down
|
•The ATM line is up and operating correctly.
•The ATM interface has been disabled with the shutdown command.
•The ATM line is down, possibly because the ADSL cable is disconnected or because the wrong type of cable is connected to the ATM port.
|
ATM0.1 is up, line protocol is up
Other possible messages:
ATM0.1 is administratively down, line protocol is down
ATM0.1 is down, line protocol is down
|
•The first ATM subinterface is up and operating correctly.
•The ATM subinterface has been disabled with the shutdown command.
•The ATM subinterface is down, possibly because the ATM line has been disconnected (by the service provider).
|
Ethernet0 is up, line protocol is up
Other possible messages:
Ethernet0 is up, line protocol is down
Ethernet0 is administratively down, line protocol is down
|
•The Ethernet interface is connected to the network and operating correctly.
•The Ethernet interface has been correctly configured and enabled, but the Ethernet cable might be disconnected from the LAN.
•The Ethernet interface has been disabled with the shutdown command, and the interface is disconnected.
|
Dialer1 is up, line protocol is up
Another possible message:
Dialer1 is down, line protocol is down
|
•Dialer1 is up and operating correctly.
•Dialer1 is not operating, possibly because the interface has been brought down with the shutdown command or the ADSL cable is disconnected.
|
Dialer1 is down, line protocol is down
|
•This is a standard message and does not indicate anything wrong with the configuration
|
show atm interface Command
To display ATM-specific information about an ATM interface, use the show atm interface atm0 privileged EXEC command. Following is the command syntax:
The following is an example of output from the show interface atm command:
AAL enabled: AAL5 , Maximum VCs:11, Current VCCs:0
Maximum Transmit Channels:0
PLIM Type:INVALID - 640Kbps, Framing is INVALID,
DS3 lbo:short, TX clocking:LINE
0 input, 0 output, 0 IN fast, 0 OUT fast
Table 9-3 describes the fields shown in the command output.
Table 9-3 show atm interface Command Output Description
Field
|
Description
|
ATM interface
|
Interface number. Always 0 for the Cisco 827 routers.
|
AAL enabled
|
Type of AAL enabled. The Cisco 827 routers support AAL5.
|
Maximum VCs
|
Maximum number of virtual connections this interface supports.
|
Current VCCs
|
Number of active virtual channel connections (VCCs).
|
Maximum Transmit
Channels
|
Maximum number of transmit channels.
|
Max Datagram Size
|
The configured maximum number of bytes in the largest datagram.
|
PLIM Type
|
Physical layer interface module (PLIM) type
|
debug atm Commands
This section describes how to use the debug atm commands with additional keywords to troubleshoot the router.
Before Using Debug Commands
You can use the debug commands to troubleshoot configuration problems that you might be having on your network. Debug commands provide extensive, informative displays to help you interpret any possible problems. All debug commands are entered in privileged EXEC mode, and most debug commands take no arguments. Read the information in Table 9-4 before using debug commands.
Caution Debugging is assigned a high priority in your router CPU process, and it can render your router unusable. For this reason, use debug commands only to troubleshoot specific problems. The best time to use debug commands is during periods of low network traffic so that other activity on the network is not adversely affected.
Table 9-4 Important Information About Debug Commands
Additional documentation
|
You can find additional information and documentation about the debug commands in the Debug Command Reference document on the Cisco IOS software documentation CD-ROM that came with your router.
If you are not sure where to find this document on the CD-ROM, use the Search function in the Verity Mosaic browser that comes with the CD-ROM.
|
Disabling debugging
|
To turn off any debugging, enter the undebug all command.
|
Viewing debug message
|
To view debug messages on the console, enter the logging console debug command.
|
Telnet sessions
|
If you want to use debug commands during a Telnet session with your router, you must first enter the terminal monitor command.
|
debug atm errors Command
Use the debug atm errors command to display ATM errors. The no form of this command disables debugging output. Following is the command syntax:
Following is sample debug atm errors output.
ATM errors debugging is on
01:32:02:ATM(ATM0.2):VC(3) Bad SAP received 4500
01:32:04:ATM(ATM0.2):VC(3) Bad SAP received 4500
01:32:06:ATM(ATM0.2):VC(3) Bad SAP received 4500
01:32:08:ATM(ATM0.2):VC(3) Bad SAP received 4500
01:32:10:ATM(ATM0.2):VC(3) Bad SAP received 4500
debug atm events Command
Use the debug atm events command to display ATM events. The no form of this command disables debugging output. Following is the command syntax:
This command displays ATM events that occur on the ATM interface processor and is useful for diagnosing problems in an ATM network. It provides an overall picture of the stability of the network.
If the interface is successfully communication with the DSLAM at the telephone company, the modem state is 0x10. If the interface is not communicating with the DSLAM, the modem state is 0x8.
The following output indicates that the ADSL line is up (training successful):
00:02:57: DSL: Send ADSL_OPEN command.
00:02:57: DSL: Using subfunction 0xA
00:02:57: DSL: Using subfunction 0xA
00:02:57: DSL: Sent command 0x5
00:02:57: DSL: Received response: 0x26
00:02:57: DSL: Unexpected response 0x26
00:02:57: DSL: Send ADSL_OPEN command.
00:02:57: DSL: Using subfunction 0xA
00:02:57: DSL: Using subfunction 0xA
00:02:57: DSL: Sent command 0x5
00:03:00: DSL: 1: Modem state = 0x8
00:03:02: DSL: 2: Modem state = 0x10
00:03:05: DSL: 3: Modem state = 0x10
00:03:07: DSL: 4: Modem state = 0x10
00:03:09: DSL: Received response: 0x24
00:03:09: DSL: Sent command 0x11
00:03:09: DSL: Received response: 0x61
00:03:09: DSL: Read firmware revision 0x1A04
00:03:09: DSL: Sent command 0x31
00:03:09: DSL: Received response: 0x12
00:03:09: DSL: operation mode 0x0001
00:03:09: DSL: SM: [DMTDSL_DO_OPEN -> DMTDSL_SHOWTIME]
In case of failure, you may see the modem state remain at 0x8 and not move to 0x10:
00:02:57: DSL: Send ADSL_OPEN command.
00:02:57: DSL: Using subfunction 0xA
00:02:57: DSL: Using subfunction 0xA
00:02:57: DSL: Sent command 0x5
00:02:57: DSL: Received response: 0x26
00:02:57: DSL: Unexpected response 0x26
00:02:57: DSL: Send ADSL_OPEN command.
00:02:57: DSL: Using subfunction 0xA
00:02:57: DSL: Using subfunction 0xA
00:02:57: DSL: Sent command 0x5
00:03:00: DSL: 1: Modem state = 0x8
00:03:00: DSL: 1: Modem state = 0x8
00:03:00: DSL: 1: Modem state = 0x8
00:03:00: DSL: 1: Modem state = 0x8
00:03:00: DSL: 1: Modem state = 0x8
00:03:00: DSL: 1: Modem state = 0x8
debug atm packet Command
Use the debug atm packet command to display per-packet debugging output. The output reports information online when a packet is received or a transmission is attempted. The no form of this command disables debugging output. Following is the command syntax:
debug atm packet [interface atm number [vcd vcd-number][vc vpi/vci number]]
no debug atm packet [interface atm number [vcd vcd-number][vc vpi/vci number]]
interface atm number
|
(Optional) ATM interface or subinterface number.
|
vcd vcd-number
|
(Optional) Number of the virtual circuit designator (VCD).
|
vc vpi/vci number
|
(Required) The vpi/vci value of the ATM PVC.
|
Following are the keywords used in this command:
The debug atm packet command displays all process-level ATM packets for both outbound and inbound packets. This command is useful for determining whether packets are being received and transmitted correctly.
Caution Because the
debug atm packet command generates a significant amount of output for every packet processed, use it only when network traffic is low so that other system activities are not adversely affected.
Below is sample debug atm packet output.
VCD:0x1 VPI:0x1 VCI:0x64 DM:0x0 SAP:AAAA CTL:03 OUI:000000 TYPE:0800 Length:0x70
01:23:48:4500 0064 0008 0000 FF01 9F80 0E00 0010 0E00 0001 0800 A103 0AF3 17F7 0000
01:23:48:0000 004C BA10 ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD
01:23:48:ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD
01:23:48:ABCD ABCD ABCD ABCD ABCD
VCD:0x1 VPI:0x1 VCI:0x64 Type:0x0 SAP:AAAA CTL:03 OUI:000000 TYPE:0800 Length:0x70
01:23:48:4500 0064 0008 0000 FE01 A080 0E00 0001 0E00 0010 0000 A903 0AF3 17F7 0000
01:23:48:0000 004C BA10 ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD
01:23:48:ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD ABCD
01:23:48:ABCD ABCD ABCD ABCD ABCD
Table 9-5 describes the fields shown in the debug atm packet command output.
Table 9-5 debug atm packet Command Output Description
Field
|
Description
|
ATM0
|
Interface that is generating the packet.
|
(O)
|
Output packet. (I) would mean receive packet.
|
Pak size
|
Packet size in bytes.
|
VCD: 0xn
|
Virtual circuit associated with this packet, where n is some value.
|
VPI: 0xn
|
Virtual path identifier for this packet, where n is some value.
|
DM: 0xn
|
Descriptor mode bits, where n is some value.
|
MUXETYPE: n
|
Multiplex type.
|
Length: n
|
Total length of the packet (in bytes) including the ATM header(s).
|
Troubleshooting Telephone Interfaces
Table 9-6 describes possible problems that your router might be experiencing and solutions for solving the problems. Table 9-7 describes the applicable debug commands.
Table 9-6 Symptoms of Telephone Interfaces Trouble
Symptom
|
Possible Problem
|
Solution
|
Even though you have devices connected to ports 1 and 2, all calls are going to port 1.
|
You have not created dial peers.
|
Create dial peers.
|
You cannot make outgoing calls.
|
You have not specified all ISDN directory numbers with a SPID (North America only).
|
Check the settings of the isdn spid 1 and isdn spid 2 commands to make sure that you have specified all ISDN directory numbers for each SPID.
|
Even though you have created dial peers and set up distinctive ringing and ISDN voice priority, calls meant for secondary or tertiary ISDN directory numbers are routed to the primary number.
|
Incorrect dial peer, distinctive ringing, or ISDN voice priority configurations.
|
•Check dial peer, distinctive ringing, or ISDN voice priority configurations
•Use the debug q931 command.
|
Table 9-7 Troubleshooting Telephone Interface
Command
|
Possible Problem
|
Solution
|
debug pots driver
[1 | 2]
(privileged EXEC mode)
|
Caller ID device is not working either because you have not ordered the feature or because your device is not supported.
|
Contact your telephone service provider to verify that you ordered caller ID or to determine if there is a problem with the feature.
|
debug pots csm [1 | 2]
(privileged EXEC mode)
|
One of your dial peers might contain an invalid destination.
|
Check the settings of the destination pattern in each dial peer. If a setting is incorrect, use the destination-pattern ldn command.
|
Troubleshooting Serial Line Problems
This section describes how to troubleshoot problems in the following areas:
•Synchronous channel service unit/data service unit (CSU/DSU) clocking
•Synchronous leased lines
•Asynchronous dial-up lines
•Frame Relay
•X.25
Synchronous CSU/DSU Clocking Problems
Clocking conflicts in serial connections can lead to either chronic loss of connection service or to degraded performance. This section describes how to detect and solve clocking problems with synchronous CSU/DSUs.
Detecting Problems
Use the following steps to detect clocking conflicts on your serial interface:
Step 1 Enter the show interfaces serial 0 privileged EXEC command on the routers at both ends of the link.
Step 2 Examine the output for cyclic redundancy check (CRC) or framing errors and aborts.
If the number of CRC or framing errors exceeds an approximate range of 0.5 to 2.0 percent of traffic on the serial interface, clocking problems are likely to exist somewhere in the WAN.
Step 3 Isolate the source of the clocking conflicts by performing a series of ping tests and loopback tests (both local and remote).
Step 4 Reenter the show interfaces serial 0 privileged EXEC command on the routers at both ends of the link. Determine if CRC and framing errors are increasing and if so, where they are accumulating.
If input errors are accumulating on both ends of the connection, clocking of the CSU is the likely problem. If input errors are accumulating on one end of the connection, clocking of the DSU or cabling are the likely problems. If aborts are occurring on one end of the connection, the other end could be sending bad information or there could be a problem with the serial line.
Table 9-8 describes possible CSU/DSU clocking problems your router might be experiencing and the solutions for solving those problems.
Table 9-8 Synchronous CSU/DSU Clocking Problems
Symptom
|
Solution
|
Incorrect CSU configuration
|
Perform the following tasks in the following order:
•Determine whether the CSUs at both ends of the serial line agree on the clock source (local or line).
•If the CSUs do not agree, configure them to do so.
•Check the line build out (LBO) setting on the CSU to ensure that the impedance matches that of the physical line. For information on configuring your CSU, refer to your CSU documentation.
|
Incorrect DSU configuration
|
Perform the following steps in the following order:
•Determine whether the DSUs at both ends of the serial line have serial clock transmit external (SCTE) mode enabled.
•If SCTE is not enabled on both ends of the connection, enable it.
•For any interface that is connected to a line of 128 kbps or faster, SCTE must be enabled.
•Make sure that ones density is maintained, which requires that the DSU use the same framing and coding schemes (for example, Extended Superframe Format [ESF] and Binary 8-Zero Substitution [B8ZS]) that are used by the leased line or other carrier service.
•Check with your leased line provider for information on its framing and coding schemes.
•If your carrier service uses Alternate Mark Inversion (AMI) coding, either invert the transmit clock on both sides of the link or run the DSU in bit-stuff mode. For information on configuring your DSU, refer to your DSU documentation.
|
Performing Ping Tests
Use the following steps to perform ping tests:
Step 1 Put the CSU or DSU into local loopback mode.
Step 2 Use the ping privileged EXEC command to send different data patterns and packet sizes.
Performing Loopback Tests
These loopback tests do not apply to Frame Relay or X.25 networks.
Local Loopback Tests
Follow the steps below to perform local loopback tests:
Step 1 Place the CSU/DSU in local loop mode (refer to your CSU/DSU documentation).
In local loop mode, the use of the line clock (from the T1 service) is terminated, and the DSU is forced to use the local clock.
Step 2 Enter the show interfaces serial 0 privileged EXEC command to determine if the line status changes from "line protocol is down" to "line protocol is up (looped)," or if it remains down.
If the line protocol comes up when the CSU or DSU is in local loopback mode, a problem could be occurring on the remote end of the serial connection. If the status line does not change state, there is a possible problem in the router, connecting cable, or CSU/DSU.
If the problem appears to be local, enter the debug serial interface privileged EXEC command and go on to the next step.
Step 3 Take the CSU/DSU out of local loop mode.
When the line protocol is down, the debug serial interface command output will indicate that keepalive counters are not incrementing.
Step 4 Place the CSU/DSU in local loop mode again.
This action should cause the keepalive packets to begin to increment. Specifically, the values for mineseen and yourseen keepalives will increment every 10 seconds. This information will appear in the debug serial interface output.
If the keepalives do not increment, there may be a timing problem on the interface card or on the network.
Step 5 Check the local router and CSU/DSU hardware, and any attached cables.
Make certain the cables are within the recommended lengths (no more than 50 feet [15.24 meters], or 25 feet [7.62 meters] for a T1 link). Make certain the cables are attached to the proper ports. Swap faulty equipment as necessary.
Remote Loopback Tests
Follow the steps below to perform remote loopback tests:
Step 1 Put the remote CSU or DSU into remote loopback mode (refer to the your CSU/DSU documentation).
Step 2 Enter the show interfaces serial 0 privileged EXEC command to determine if the line protocol remains up with the status line indicating "Serial x is up, line protocol is up (looped)," or if it goes down with the status line indicating "line protocol is down."
If the line protocol remains up (looped), the problem is probably at the remote end of the serial connection (between the remote CSU/DSU and the remote router). Perform both local and remote tests at the remote end to isolate the problem source.
If the line status changes to "line protocol is down" when remote loopback mode is activated, make certain that ones density is being properly maintained. The CSU/DSU must be configured to use the same framing and coding schemes used by the leased-line or other carrier service (for example, ESF and B8ZS).
Synchronous Leased Line Problems
Follow the steps below to troubleshoot problems with your synchronous leased line:
Step 1 From privileged EXEC command mode, enter the show interfaces serial 0 command.
If you see the line Serial0 is up, line protocol is up, the serial line is functioning properly. You do not need to take further action.
Step 2 If you see one of the following messages, refer to Table 9-9:
•Serial 0 is down, line protocol is down.
•Serial 0 is up, line protocol is down.
•Serial 0 is up, line protocol is up (looped).
•Serial 0 is administratively down, line protocol is up.
Table 9-9 Leased Line Problems
Line State
|
Problem
|
Solution
|
Serial 0 is down; line protocol is down.
|
The router is not sensing a carrier detect (CD) signal as a result of one of the following:
•Faulty or incorrect cabling of the router.
•Local router hardware failure.
•Local CSU/DSU hardware failure.
•WAN service provider problem, such as the line is down or not connected to the CSU/DSU.
|
Following are some steps you can take to isolate the problem:
•Refer to the Cisco 805 Router Hardware Installation Guide to confirm that you are using the correct serial cable to connect the CSU/DSU and that you connected the CSU/DSU correctly.
•Connect the leased line to another port, if possible. If the connection comes up, there is a hardware failure. Contact your Cisco reseller.
•Check the LEDs on the CSU/DSU for CD activity.
•Contact your WAN service provider.
|
Serial 0 is up; line protocol is down.
|
Possible causes for this line state are:
•Router hardware failure.
•Local or remote CSU/DSU hardware failure.
•Local or remote router misconfigured.
•The serial clock transmit external is not set on the CSU/DSU.
•The remote router is not sending keepalive packets.
•Problem with the leased line.
|
Following are some steps you can take to isolate the problem:
•Refer to the Cisco 805 Router Hardware Installation Guide to confirm that you are using the correct serial cable to connect the CSU/DSU and that you connected the CSU/DSU correctly.
•Connect the leased line to another port, if possible. If the connection comes up, there is a hardware failure. Contact your Cisco reseller.
•Check the LEDs on the CSU/DSU for CD activity.
•Perform CSU/DSU loopback tests. During local loopback, enter the show interfaces serial 0 command. If the line protocol is shown as up, there might be a problem with the WAN service provider, or the remote router is down.
•Contact your WAN service provider.
|
Serial 0 is up; line protocol is up (looped).
|
The possible cause is a loop in the circuit. The sequence number in the keepalive packet changes to a random number when a loop is first detected. If the same random number is returned over the line, a loop exists.
|
Following are some steps you can take to isolate the problem:
•Use the write terminal privileged EXEC command to display any instances of the loopback command. If the router has been configured with the loopback command, enter the no loopback command to remove the loop.
•Check to see whether the CSU/DSU is configured in manual loopback mode. If it is, disable manual loopback.
•Reset the CSU/DSU.
•If you are unable to isolate the problem, contact your WAN service provider for help with troubleshooting.
|
Serial 0 is administratively down; line protocol is up.
|
The possible causes for this state are:
•The serial interface has been disabled with the shutdown command.
•Different interfaces on the router are using the same IP address.
|
Following are some steps you can take to isolate the problem:
•Use the show configuration privileged EXEC command to display the serial port configuration. If "shutdown" is displayed after "interface Serial0," use the no shutdown command in serial interface configuration mode to enable the interface.
•Use the show interface privileged EXEC command to display the IP addresses for all router interfaces. Take the appropriate action to assign a unique IP address to each router interface. (If you set up your network per the sample networks in the this guide, refer to that particular sample network for information on how to assign a unique IP address to the router interfaces.
|
Asynchronous Dial-Up Problems
This section describes how to use the show line 1 command to troubleshoot problems with the connection between your modem and router. It also describes the following symptoms, problems, and solutions:
•Troubleshooting Problems with Modem and Router Connection
•No Connectivity Between Modem and Router
•Modem Does Not Dial
•Modem Does Not Answer
•Modem Hangs Up Shortly After Connecting
•Dial-Up Client Receives No EXEC Prompt
•Dial-Up Session Sees Garbage
•Dial-Up Session Ends Up in Existing Session
•Modem Cannot Send or Receive Data
•Modem Cannot Send or Receive IP Data
•Modem Does Not Disconnect Properly
•Link Deactivates Too Quickly
•Link Does Not Deactivate or Stays Activated Too Long
•Poor Dial-Up Connection Performance
Troubleshooting Problems with Modem and Router Connection
Follow the steps below to troubleshoot problems with the connection between your modem and router:
Step 1 In privileged EXEC command mode, enter the show line 1 command.
Check the Modem state field in the output. If the modem state is Idle and CTS noDSR DTR RTS, the connection between your modem and router is functioning properly.
Step 2 If you see one of the following modem states, see Table 9-10:
•Ready -
•Ready not CTS noDSR DTR RTS
•Ready CTS DSR DTR RTS
•Ready CTS* DSR* DTR RTS
Table 9-10 Problems with Modem and Router Connection
Modem State
|
Problem
|
Ready -
|
•Modem control is not configured on the router. Enter the modem inout command in serial interface configuration mode.
•A session exists on the line. Enter the show users privileged EXEC command and the clear line 0 privileged EXEC command to stop the session if desired.
•Data set ready (DSR) is high. There are two possible reasons for this:
–Cabling problems—If your modem connector uses DB-25 pin 6 and has no pin 8, you must move the pin from 6 to 8 or get the appropriate connector.
–Modem configured for data carrier detect (DCD) always high—The modem should be reconfigured to have DCD high only on carrier detect (CD), which is usually done with the &C1 modem command. Check your modem documentation for the exact syntax for your modem.
•If your software does not support modem control, you must configure the router line to which the modem is connected with the no exec command in asynchronous line configuration mode. Clear the line with the clear line privileged EXEC command, initiate a reverse Telnet session with the modem, and reconfigure the modem so that DCD is high only on CD. End the Telnet session by entering disconnect and reconfigure the router line with the EXEC command in asynchronous line configuration mode.
|
Ready noCTS noDSR DTR RTS
|
•The modem is turned off.
•The modem is not properly connected to the router. Refer to the Cisco 805 Router Hardware Installation Guide for information on how to select the serial cable and how to connect the modem.
•The modem is not configured for hardware flow control. Disable hardware flow control on the router by entering the no flowcontrol hardware command in asynchronous line configuration mode. Enable hardware flow control on the modem via a reverse Telnet session. (Consult your modem documentation.) Reenable hardware flow control on the router by entering the flowcontrol hardware command in asynchronous line configuration mode.
|
Ready CTS DSR DTR RTS
|
•Incorrect cabling. Refer to the Cisco 805 Router Hardware Installation Guide for information on how to select the serial cable.
•The modem is configured for DCD always high. Reconfigure the modem so that DCD is only high on CD, which is usually done with the &C1 modem command. Check your modem documentation for the exact syntax for your modem.
Configure the router line to which the modem is connected by entering the no exec command in asynchronous line configuration mode. Clear the line with the clear line privileged EXEC command, initiate a reverse Telnet session with the modem, and reconfigure the modem so that DCD is high only on CD. End the Telnet session by entering disconnect. Reconfigure the router line with the exec command in asynchronous line configuration mode.
|
Note Ready CTS* DSR* DTR RTS1
|
If this string appears in the Modem state field, modem control is probably not enabled on the router. Enter the modem inout command in asynchronous line configuration mode to enable modem control on the line.
|
No Connectivity Between Modem and Router
The connection between a modem and a Cisco router does not work. Attempts to initiate a reverse Telnet session to the modem have no result, or you receive a "Connection Refused by Foreign Host" message.
Table 9-11 outlines the problems that might cause this connectivity failure and describes possible solutions.
Table 9-11 No Connectivity Between Modem and Router
Problem
|
Solution
|
Incorrect cabling.
|
Check the cabling between the modem and the router. Refer to the Cisco 805 Router Hardware Installation Guide for information on how to select the serial cable and how to connect the modem.
|
Hardware problem.
|
•Check the cabling between the modem and the router. Refer to the Cisco 805 Router Hardware Installation Guide for information on how to select the serial cable and how to connect the modem.
•Check all hardware for damage, including cabling (broken wires), adapters (loose pins), ports, and modem.
|
Modem control is not enabled on the router.
|
•Use the show line 1 privileged EXEC command on the router. The output should show inout or RIisCD in the Modem column, which indicates that modem control is enabled on the line of the router.
•If necessary, configure modem control by using the modem inout command in asynchronous line configuration mode.
|
Modem Does Not Dial
Dial-up sessions cannot be established because the modem does not dial properly.
Table 9-12 outlines the problems that might cause this symptom and describes solutions to those problems.
Table 9-12 Modem Does Not Dial
Problem
|
Solution
|
Incorrect cabling
|
Check the cabling between the modem and the router. Refer to the Cisco 805 Router Hardware Installation Guide for information on how to select the serial cable and how to connect the modem.
|
Modem hardware problem
|
Check the modem's physical connection. Make sure the modem is on and is connected securely to the correct port. Make sure the transmit and receive indicator lights flash when the chat script is running.
|
No packets of interest defined
|
•Use the show running-config privileged EXEC command to view the router configuration. Check the dialer-list command entries to see which access lists, if any, are being used to define interesting traffic.
•Make sure that the access lists referenced by the dialer-list commands specify all traffic that should bring the link up (interesting traffic).
•If necessary, modify the access list commands so that they define the proper traffic as interesting.
|
Missing chat script
|
•Use the debug chat privileged EXEC command to check whether there is a chat script running.
•If there is no chat script running, use the start-chat privileged EXEC command or another appropriate command to start the chat script on the line.
|
Bad chat script
|
•Establish a reverse Telnet session to the modem, and step through each step of the chat script.
•Verify that the command response to each chat script step is correct.
•Fix any inconsistencies you find in the chat script.
|
Modem Does Not Answer
When attempting to open a dial-up connection to a modem, the modem does not answer the call.
Table 9-13 describes possilbe causes of and solutions to this problems.
Table 9-13 Modem Does Not Answer
Problem
|
Solution
|
Incorrect cabling
|
Check the cabling between the modem and the router. Refer to the Cisco 805 Router Hardware Installation Guide for information on how to select the serial cable and how to connect the modem.
|
Modem control not enabled on router
|
•Observe the remote modem to see whether it is receiving a data terminal ready (DTR) signal from the router. Most modems have a DTR indicator light. Check the modem documentation to interpret the indicator lights.
•If the DTR indicator light is on, the modem is seeing a DTR signal from the router. You can also enter the show line 1 privileged EXEC command to check for DTR. If the Modem state shows the string noDTR, then the router is configured to hold DTR low, and the modem is not seeing a DTR signal.
•Configure modem control by entering either the modem inout or the modem ri-is-cd command in the asynchronous line configuration mode.
|
Remote modem not set to auto-answer
|
•Check the remote modem to see if it is set to auto-answer. Usually, an AA indicator light will be on when auto-answer is set.
•Set the remote modem to auto-answer if it is not already set. To find out how to verify and change the modem's settings, refer to your modem documentation.
|
Wrong telephone line attached to remote modem
|
•Make sure that you are using the correct telephone line. Replace the remote modem with a telephone, and call again. If the phone rings, you are using the correct telephone line.
•Contact the telephone company to make sure that the line is good.
|
Remote modem not attached to a router
|
•Make sure that the remote modem is attached to a router or other device that is asserting DTR.
•Most modems have an LED indicator for DTR. Check to make sure that this indicator comes on.
|
Modem Hangs Up Shortly After Connecting
A dial-up connection is successful but the modem hangs up after 30 to 90 seconds.
Table 9-14 outlines the problems that might cause this symptom and describes solutions to those problems.
Table 9-14 Modem Hangs Up Shortly After Connecting
Problem
|
Solution
|
Modem speed setting is not locked.
|
•Enter the show line 1 privileged EXEC command on the router. The output for the serial port should indicate the currently configured transmit (Tx) and receive (Rx) speeds.
•If the line is not configured to the correct speed, use the speed command in asynchronous line configuration mode to set the speed on the router line. Set the value to the highest speed in common between the modem and the router port. If for some reason you cannot use flow control, limit the line speed to 9600 bps. Faster speeds are likely to result in lost data.
•Use the show line 1 command again, and confirm that the line speed is set to the desired value.
•When you are certain that the router line is configured for the desired speed, initiate a reverse Telnet session to the modem on that line.
•Use a modem command string that includes the lock DTE speed command for your modem. See your modem documentation for exact configuration command syntax.
The lock DTE speed command, which might also be referred to as port rate adjust or buffered mode, is often related to the way in which the modem handles error correction. This command varies widely between modems.
Locking the modem speed ensures that the modem always communicates with the Cisco router at the speed configured on the Cisco serial port. If this command is not used, the modem will revert to the speed of the data link (the telephone line) instead of communicating at the speed configured on the router.
|
Modem control is not enabled on the router.
|
•Use the show line 1 privileged EXEC command on the router. The output for the port should show inout or RIisCD in the Modem column, which indicates that modem control is enabled on the line of the router.
•If necessary, configure modem control by using the modem inout command in asynchronous line configuration mode.
|
PPP authentication fails.
|
•Use the debug ppp chap privileged EXEC command to see whether PPP authentication was successful. Check the output for the phrase Passed authentication with remote. If you see this output, authentication was successful.
•If PPP authentication was not successful, verify the username and password configured on the router. The username and password you enter must be identical to those configured on the router. Usernames and passwords are case-sensitive.
|
Local router not waiting long enough to connect.
|
•Enter the show dialer privileged EXEC command to see the configured dialer timeout. A timeout value of less than 120 seconds will not be long enough.
•Configure the local router to wait longer for the connection by entering the dialer wait-for-carrier-time command in the serial interface configuration mode. Make sure that you specify at least a 120-second timeout.
|
Chat script problem.
|
•Enter the debug chat privileged EXEC command. If you see the output "Success" at the end of the chat script, the chat script completed successfully.
•Make the timeout in the chat script longer at the point where it fails.
•If the problem persists, verify that the command response to each chat script step is correct. Open a reverse Telnet session to the modem and step through the chat script.
•Fix any inconsistencies you find in the chat script.
|
Dial-Up Client Receives No EXEC Prompt
A remote dial-up client opens a session and appears to be connected, but the user does not receive an EXEC prompt (for example, a Username> or Router> prompt).
Table 9-15 outlines the problems that might cause this symptom and describes solutions to those problems.
Table 9-15 Dial-Up Client Receives No EXEC Prompt
Problem
|
Solution
|
Autoselect is enabled on the line
|
Try to access privileged EXEC mode by entering a carriage return.
|
Line is configured with the no exec command.
|
•Use the show line 1 privileged EXEC command to view the status of the appropriate line. Check the Capabilities field for the phrase says EXEC suppressed. If this is the case, the no exec line configuration command is enabled.
•Configure the exec command in asynchronous line configuration mode to allow EXEC sessions to be initiated.
|
Flow control is not enabled, is enabled only on one device (either DTE or DCE), or is misconfigured.
|
•Enter the show line 0 privileged EXEC command, and look for the following in the Capabilities field:
Capabilities: Hardware Flowcontrol In, Hardware Flowcontrol
Out...
If there is no mention of hardware flow control in this field, hardware flow control is not enabled on the line.
•Configure hardware flow control on the line using the flowcontrol hardware command in asynchronous line configuration mode. If for some reason you cannot use flow control, limit the line speed to 9600 bps. Faster speeds are likely to result in lost data.
•After enabling hardware flow control on the router line, initiate a reverse Telnet session to the modem via that line.
•Use a modem command string that includes the RTS/CTS flow command for your modem. This command ensures that the modem is using the same method of flow control (that is, hardware flow control) as the Cisco router. See your modem documentation for the exact configuration command syntax.
|
Modem speed setting is not locked.
|
•Enter the show line 1 privileged EXEC command on the router. The output for the serial port should indicate the currently configured transmit (Tx) and receive (Rx) speeds.
•If the line is not configured to the correct speed, use the speed command in asynchronous line configuration mode to set the speed on the router line. Set the value to the highest speed in common between the modem and the router port. If for some reason you cannot use flow control, limit the line speed to 9600 bps. Faster speeds are likely to result in lost data.
•Use the show line 1 command again, and confirm that the line speed is set to the desired value.
•When you are certain that the router line is configured for the desired speed, initiate a reverse Telnet session to the modem on that line.
•Use a modem command string that includes the lock DTE speed command for your modem. See your modem documentation for the exact configuration command syntax.
The lock DTE speed command, which might also be referred to as port rate adjust or buffered mode, is often related to the way in which the modem handles error correction. This command varies widely between modems.
Locking the modem speed ensures that the modem always communicates with the Cisco router at the speed configured on the Cisco serial port. If this command is not used, the modem will revert to the speed of the data link (the telephone line) instead of communicating at the speed configured on the router.
|
Dial-Up Session Sees Garbage
Attempts to establish remote dial-up sessions over a modem to a Cisco router return garbage and ultimately result in no connection to the remote site. Users might see a Connection Closed by Foreign Host message.
Table 9-16 outlines causes of this problem and describes possible solutions.
Table 9-16 Dial-Up Session Sees Garbage
Problem
|
Solution
|
Modem speed setting is not locked.
|
•Enter the show line 1 privileged EXEC command on the router. The output for the serial port should indicate the currently configured transmit (Tx) and receive (Rx) speeds.
•If the line is not configured to the correct speed, use the speed command in asynchronous line configuration mode to set the speed on the router line. Set the value to the highest speed in common between the modem and the router port. If for some reason you cannot use flow control, limit the line speed to 9600 bps. Faster speeds are likely to result in lost data.
•Use the show line 1 command again, and confirm that the line speed is set to the desired value.
•When you are certain that the router line is configured for the desired speed, initiate a reverse Telnet session to the modem on that line.
•Use a modem command string that includes the lock DTE speed command for your modem. See your modem documentation for the exact configuration command syntax.
The lock DTE speed command, which might also be referred to as port rate adjust or buffered mode, is often related to the way in which the modem handles error correction. This command varies widely between modems.
Locking the modem speed ensures that the modem always communicates with the Cisco router at the speed configured on the Cisco serial port. If this command is not used, the modem will revert to the speed of the data link (the telephone line) instead of communicating at the speed configured on the router.
|
Dial-Up Session Ends Up in Existing Session
A remote dial-up session ends up in an already existing session initiated by another user. That is, instead of getting a login prompt, a dial-up user sees a session established by another user (which might be a UNIX command prompt, a text editor session, and so forth).
Table 9-17 outlines causes of this problems and describes possible solutions.
Table 9-17 Dial-Up Session Ends Up in Existing Session
Problems
|
Solutions
|
Incorrect cabling.
|
Check the cabling between the modem and the router. Refer to the Cisco 805 Router Hardware Installation Guide for information on how to select the serial cable and how to connect the modem.
|
Modem control is not enabled on the router.
|
•Enter the show line 1 privileged EXEC command on the router. The output for the serial port should show inout or RIisCD in the Modem column, which indicates that modem control is enabled on the router line.
•Configure modem control by entering either the modem inout or the modem ri-is-cd command in the asynchronous line configuration mode.
|
Modem configured for DCD is always high.
|
•The modem should be reconfigured to have DCD high only on CD, which is usually configured with the &C1 modem command string. Check your modem documentation for the exact syntax for your modem.
•You might have to configure the router line to which the modem is connected with the no exec command in asynchronous line configuration mode. Clear the line with the clear line privileged EXEC command, initiate a reverse Telnet session with the modem, and reconfigure the modem so that DCD is high only on CD.
•End the Telnet session by entering disconnect and reconfigure the router line with the exec line configuration command.
|
Modem Cannot Send or Receive Data
After a dial-up connection is established, a modem cannot send or receive data of any kind.
Table 9-18 outlines causes of this problem and describes possible solutions.
Table 9-18 Modem Cannot Send or Receive Data
Problem
|
Solution
|
Modem speed setting is not locked.
|
•Enter the show line 1 privileged EXEC command on the router. The output for the serial port should indicate the currently configured transmit (Tx) and receive (Rx) speeds.
•If the line is not configured to the correct speed, use the speed command in asynchronous line configuration mode to set the speed on the router line. Set the value to the highest speed in common between the modem and the router port. If for some reason you cannot use flow control, limit the line speed to 9600 bps. Faster speeds are likely to result in lost data.
•Use the show line 1 command again, and confirm that the line speed is set to the desired value.
•When you are certain that the router line is configured for the desired speed, initiate a reverse Telnet session to the modem on that line.
•Use a modem command string that includes the lock DTE speed command for your modem. See your modem documentation for the exact configuration command syntax.
The lock DTE speed command, which might also be referred to as port rate adjust or buffered mode, is often related to the way in which the modem handles error correction. This command varies widely between modems.
Locking the modem speed ensures that the modem always communicates with the Cisco router at the speed configured on the Cisco serial port. If this command is not used, the modem will revert to the speed of the data link (the telephone line) instead of communicating at the speed configured on the router.
|
Hardware flow control not configured on local or remote modem or router
|
•Enter the show line 0 privileged EXEC command, and look for the following in the Capabilities field:
Capabilities: Hardware Flowcontrol In, Hardware Flowcontrol
Out...
If there is no mention of hardware flow control in this field, hardware flow control is not enabled on the line.
•Configure hardware flow control on the line using the flowcontrol hardware command in asynchronous line configuration mode. If for some reason you cannot use flow control, limit the line speed to 9600 bps. Faster speeds are likely to result in lost data.
•After enabling hardware flow control on the router line, initiate a reverse Telnet session to the modem via that line.
•Use a modem command string that includes the RTS/CTS flow command for your modem. This command ensures that the modem is using the same method of flow control (that is, hardware flow control) as the Cisco router is using. See your modem documentation for the exact configuration command syntax.
|
Problem with dialing modem
|
Make sure that the dialing modem is operational and is securely connected to the correct port. Check whether another modem works when connected to the same port.
|
Modem Cannot Send or Receive IP Data
After a dial-up connection is established, a modem cannot send or receive IP data.
Table 9-19 outlines causes of this problem and describes possible solutions.
Table 9-19 Modem Cannot Send or Receive IP Data
Problem
|
Solution
|
IP routing not enabled on local or remote router
|
Make sure that IP routing is enabled on the local and remote routers.
|
No default gateway specified on PC
|
•Enter the show slip privileged EXEC command. Make sure that the specified IP address is the same as the default gateway specification on the PC.
•Check the specified default gateway address on the PC. If the IP address is not correct, specify the correct address. For instructions on verifying and changing the default gateway address on the workstation, refer to the vendor documentation.
|
Hardware flow control not configured on local or remote modem or router
|
•Enter the show line 0 privileged EXEC command, and look for the following in the Capabilities field:
Capabilities: Hardware Flowcontrol In, Hardware Flowcontrol
Out...
If there is no mention of hardware flow control in this field, hardware flow control is not enabled on the line.
•Configure hardware flow control on the line using the flowcontrol hardware command in asynchronous line configuration mode. If for some reason you cannot use flow control, limit the line speed to 9600 bps. Faster speeds are likely to result in lost data.
•After enabling hardware flow control on the router line, initiate a reverse Telnet session to the modem via that line.
•Use a modem command string that includes the RTS/CTS flow command for your modem. This command ensures that the modem is using the same method of flow control (that is, hardware flow control) as the Cisco router is using. See your modem documentation for the exact configuration command syntax.
|
Static routes not configured
|
•Use the show ip route privileged EXEC command to check whether there is a static route to the remote network in the routing table.
•If there is no static route to the remote network, configure one, using the ip route command. The static route should point to the remote network.
|
Domain Name System (DNS) server not specified on router or workstation
|
•Check whether the workstation and router both have DNS information specified. On the router, use the show running-config privileged EXEC command to see if DNS is configured. For information on verifying the workstation configuration, refer to the vendor documentation.
•If the router and workstation are not configured to use DNS, use the ip domain-lookup, ip domain-name, and ip name-server commands to configure the router.
•Configure a DNS server address in the TCP/IP software on the PC. For more information, refer to the vendor documentation.
|
Modem Does Not Disconnect Properly
The modem does not disconnect properly. Connections to the modem do not terminate when the quit command is entered.
Table 9-20 outlines causes of this problem and describes possible solutions.
Table 9-20 Modem Does Not Disconnect Properly
Problem
|
Solution
|
Modem is not sensing DTR.
|
Enter the hangup DTR modem command string. This command tells the modem to drop carrier when the DTR signal is no longer being received. For the exact syntax of this command, see the your modem documentation.
|
Modem control is not enabled on the router.
|
•Use the show line 1 privileged EXEC command on the router. The output should show inout or RIisCD in the Modem column, which indicates that modem control is enabled on the line of the router.
•If necessary, configure modem control by using the modem inout command in asynchronous line configuration mode.
|
Link Deactivates Too Quickly
After a dial-up connection is established, the link deactivates too quickly.
Table 9-21 outlines causes of this problem and describes possible solutions.
Table 9-21 Link Deactivates Too Soon
Problem
|
Solution
|
Dialer timeout is too short
|
•Use the show running-config privileged EXEC command to view the router configuration. Check the value configured with the dialer idle-timeout command.
•Increase the timeout value, using the dialer idle-timeout seconds command. The default is 120 seconds.
|
Dialer lists are too restrictive
|
•Use the show running-config privileged EXEC command to view the router configuration. Check the access lists, if any, referenced by dialer list commands.
•Make sure that the access lists describe all the traffic that should keep the link active. Reconfigure the access lists to include additional traffic if necessary.
|
Link Does Not Deactivate or Stays Activated Too Long
After a dial-up connection is established, the link activates indefinitely or stays activated too long in an idle state.
Table 9-22 outlines causes of this problem and describes possible solutions.
Table 9-22 Link Does Not Deactivate or Stays Activated Too Long
Problem
|
Solution
|
Dialer lists not restrictive enough
|
•Use the show running-config privileged EXEC command to view the router configuration. Check the access lists, if any, referenced by dialer list commands.
•Make sure that the access lists do not describe traffic that should not keep the link active. Reconfigure the access lists if necessary.
|
Modems misconfigured
|
Make sure that the local and remote modems are properly configured. In particular, both modems should be configured to disconnect on loss of DTR (Hangup DTR). For the exact syntax of this command, see your modem documentation.
|
Poor Dial-Up Connection Performance
After a dial-up connection is established, performance over the link is slow or unreliable, often as a result of a high rate of data loss.
Table 9-23 outlines causes of this problem and describes possible solutions.
Table 9-23 Poor Dial-Up Connection Performance
Problem
|
Solution
|
Error correction is not configured on the modem.
|
Make certain the modem is configured for error correction. For the exact syntax of the command, see your modem documentation.
|
Flow control is not enabled, is enabled only on one device (either DTE or DCE), or is misconfigured.
|
•Enter the show line 0 privileged EXEC command, and look for the following in the Capabilities field:
Capabilities: Hardware Flowcontrol In, Hardware Flowcontrol
Out...
If there is no mention of hardware flow control in this field, hardware flow control is not enabled on the line.
•Configure hardware flow control on the line using the flowcontrol hardware command in asynchronous line configuration mode. If for some reason you cannot use flow control, limit the line speed to 9600 bps. Faster speeds are likely to result in lost data.
•After enabling hardware flow control on the router line, initiate a reverse Telnet session to the modem via that line.
•Use a modem command string that includes the RTS/CTS flow command for your modem. This command ensures that the modem is using the same method of flow control (that is, hardware flow control) as the Cisco router. See your modem documentation for the exact configuration command syntax.
|
Congestion or line noise.
|
•If the network is congested, dial-up connections can freeze for a few seconds. The only solution is to reduce congestion on the network by increasing bandwidth or redesigning the network.
•Line noise can also freeze up a dial-up connection. For information on how to account for line noise for your modem, refer to the vendor documentation.
|
Frame Relay Problems
This section describes how to troubleshoot the following Frame Relay symptoms:
•Frame Relay Link Is Down
•Cannot Ping Remote Router
•Cannot Ping End to End
Frame Relay Link Is Down
Connections over a Frame Relay link fail. Table 9-24 outlines causes of this problem and describes possible solutions.
Table 9-24 Frame Relay Link Is Down
Problem
|
Solution
|
Cabling, hardware, or carrier problem
|
Perform these steps on the local and remote routers.
•Use the show interfaces serial 0 command to see if the interface and line protocol are up.
•If the interface and line protocol are down, refer to the Cisco 805 Router Hardware Installation Guide to confirm that you are using the correct serial cable to connect the CSU/DSU and that you connected the CSU/DSU correctly. Make sure that cables are securely attached.
•If the cable is correct, try moving it to a different port. If that port works, then the first port is defective. Replace the router.
•If the cable does not work on the second port, replace the cable. If it still does not work, there might be a problem with the DCE. Contact your carrier about the problem.
|
Local management interface (LMI) type mismatch
|
•Use the show interfaces serial 0 command to check the state of the interface.
•If the output shows the interface is up but the line protocol is down, enter the show frame-relay lmi privileged EXEC command to see which LMI type is configured on the Frame Relay interface.
•Make sure that the LMI type is the same for all devices in the path from source to destination. Enter the frame-relay lmi-type {ansi | cisco | q933a} command in serial interface configuration mode to change the LMI type on the router.
|
Keepalives not being sent
|
•Enter the show interfaces serial 0 command to find out if keepalives are configured. If you see a line that says "keepalives not set," keepalives are not configured.
•Use the keepalive seconds command in serial interface configuration mode to configure keepalives. The default value for this command is 10 seconds.
|
Encapsulation mismatch
|
•When connecting Cisco devices with non-Cisco devices, you must use Internet Engineering Task Force (IETF) encapsulation on both devices. Check the encapsulation type on the Cisco device by using the show frame-relay map privileged EXEC command.
•If the Cisco device is not using IETF encapsulation, use the encapsulation frame-relay ietf command in serial interface configuration mode to configure IETF encapsulation on the Cisco Frame Relay interface. For information on viewing or changing the configuration of the non-Cisco device, refer to the vendor documentation.
|
Data-link connection identifier (DLCI) inactive or deleted
|
•Enter the show frame-relay pvc privileged EXEC command to view the status of the interface PVC.
•If the output shows that the PVC is inactive or deleted, there is a problem along the path to the remote router. Check the remote router or contact your carrier to check the status of the PVC.
|
DLCI assigned to wrong subinterface
|
•Use the show frame-relay pvc privileged EXEC command to check the assigned DLCIs. Make sure that the correct DLCIs are assigned to the correct subinterface.
•If the DLCIs appear to be correct, shut down the main interface by entering the shutdown command in serial interface configuration mode, then bring the interface back up entering the no shutdown command.
|
Cannot Ping Remote Router
Attempts to ping the remote router across a Frame Relay connection fail. Table 9-25 outlines causes of this problem and describes possible solutions.
Table 9-25 Cannot Ping Remote Router
Problem
|
Solution
|
Encapsulation mismatch
|
•When connecting Cisco devices to non-Cisco devices, you must use IETF encapsulation on both devices. Check the encapsulation type on the Cisco device by using the show frame-relay map privileged EXEC command.
•If the Cisco device is not using IETF encapsulation, use the encapsulation frame-relay ietf command in serial interface configuration mode to configure IETF encapsulation on the Cisco Frame Relay interface. For information on viewing or changing the configuration of the non-Cisco device, refer to the vendor documentation.
|
DLCI inactive or deleted
|
•Enter the show frame-relay pvc privileged EXEC command to view the status of the interface PVC.
•If the output shows that the PVC is inactive or deleted, there is a problem along the path to the remote router. Check the remote router, or contact your carrier to check the status of the PVC.
|
DLCI assigned to wrong subinterface
|
•Use the show frame-relay pvc privileged EXEC command to check the assigned DLCIs. Make sure that the correct DLCIs are assigned to the correct subinterface.
•If the DLCIs appear to be correct, shut down the main interface by entering the shutdown command in serial interface configuration mode. Then bring the interface back up by entering the no shutdown command.
|
Misconfigured access list
|
•Enter the show access-list privileged EXEC command to see whether there are access lists configured on the router.
•If access lists are configured, test connectivity by disabling access lists by entering the no access-group command in global configuration mode. Check to see whether connectivity is restored.
•If connections work, reenable access lists one at a time, checking connections after enabling each access list.
•If enabling an access list blocks connections, make sure that the access list does not deny necessary traffic. Make sure to configure explicit permit statements for any traffic you want to pass.
•Continue testing access lists until all access lists are restored and connections still work.
|
frame-relay map command missing
|
•Enter the show frame-relay map privileged EXEC command to see whether an address map is configured for the DLCI.
•If you do not see an address map for the DLCI, enter the clear frame-relay-inarp privileged EXEC command. Then enter the show frame-relay map command again to see if there is now a map to DLCI.
•If there is no map to the DLCI, add a static address map by entering the frame-relay map command in serial interface configuration mode.1 For complete information on configuring Frame Relay address maps, refer to the Cisco IOS Wide-Area Networking Configuration Guide publication.
•Make sure that the DLCIs and next-hop addresses specified in frame-relay map commands are correct. The specified protocol address should be in the same network as your local Frame Relay interface.
|
No broadcast keyword in frame-relay map statements
|
•Enter the show running-config privileged EXEC command on the local and remote routers to view the router configuration. Check frame-relay map command entries to see if the broadcast keyword is specified.
•If the keyword is not specified, add the broadcast keyword to all frame-relay map commands. By default, the broadcast keyword is added to dynamic maps learned via Inverse ARP.
|
Cannot Ping End to End
Attempts to ping devices on a remote network across a Frame Relay connection fail. Table 9-26 outlines causes of this problem and describes possible solutions.
Table 9-26 Cannot Ping End to End
Problem
|
Solution
|
Split horizon problem
|
In a partially meshed Frame Relay environment, you must configure subinterfaces to avoid problems with split horizon. For detailed information on configuring subinterfaces, refer to the Wide-Area Networking Configuration Guide and Wide-Area Networking Command Reference.
|
No default gateway on workstation
|
•From a local workstation or server, try to ping the remote workstation or server. Make several attempts to ping the remote device if the first ping is unsuccessful.
•If all your attempts fail, check to see whether the local workstation or server can ping the Frame Relay interface of the local router.
•If you are unable to ping the Frame Relay interface of the local router, check the local workstation or server to see whether it is configured with a default gateway specification.
•If there is no default gateway specified, configure the device with a default gateway. The default gateway should be the address of the LAN interface of the local router. For information on viewing or changing the default gateway of the workstation or server, refer to the vendor documentation.
|
X.25 Problems
This section describes how to troubleshoot the following X.25 symptoms:
•No Connections over X.25 Link
•Excess Serial Errors on X.25 Link
No Connections over X.25 Link
Connections over an X.25 link fail.
Table 9-27 outlines causes of this problem and describes possible solutions.
Table 9-27 No Connections over X.25 Link
Problem
|
Solution
|
Incorrect cabling or bad router hardware
|
•Check all cabling and hardware for damage or wear. Replace cabling or hardware as required. For more information on the Cisco 805 router and serial cables, refer to the Cisco 805 Router Hardware Installation Guide.
•Enter the show interfaces serial 0 privileged EXEC command to determine the status of the interface.
•If the interface is down, see the "Troubleshooting Serial Line Problems" section. If the interface is up but the line protocol is down, check the Link Access Procedure, Balanced (LAPB) state in the output of the show interfaces serial 0 command.
•If the LAPB state is not CONNECT, use the debug lapb privileged EXEC command (or attach a serial analyzer) to look for set asynchronous balance mode requests (SABMs) being sent, and for UA packets being sent in reply to SABMs. If UAs are not being sent, one of the other possible problems described in this table is the likely cause.
•If the show interfaces serial 0 command indicates that the interface and line protocol are up but no connections can be made, there is probably a router or switch misconfiguration. Refer to the other possible problems outlined in this table.
|
Link is down
|
Enter the show interfaces serial 0 privileged EXEC command to determine whether the link is down. If the link is down, see the "Troubleshooting Serial Line Problems" section.
|
Misconfigured protocol parameters
|
•Enable the debug lapb privileged EXEC command and look for set asynchronous balance mode requests (SABMs) being sent. If no SABMs are being sent, disable the debug lapb command and enable the debug x25 events privileged EXEC command.
•Look for RESTART messages (for PVCs) or CLEAR REQUESTS with non-zero cause codes (for SVCs).
•To interpret X.25 cause and diagnostic codes provided in the debug x25 events output, refer to the Debug Command Reference document.
•Verify that all critical LAPB parameters (modulo, T1, N1, N2, and k) and the critical X.25 parameters (modulo, X.121 addresses, SVC ranges, PVC definitions, and default window and packet sizes) match the parameters required by the X.25 service provider.
|
Misconfigured x25 map command
|
•Use the show running-config privileged EXEC command to view the router configuration. Look for x25 map command entries under the serial interface.
•Make sure that x25 map commands specify the correct address mappings.
•If dynamic routing is being used in the network, verify that the broadcast keyword is included in the x25 map command.
•Make sure that all router X.25 configuration options match the settings of attached switches. Reconfigure the router or the switch as necessary.
•Enable the debug x25 events privileged EXEC command and look for RESTART messages (for PVCs) or CLEAR REQUESTS with non-zero cause codes (for SVCs). To interpret X.25 cause and diagnostic codes provided in the debug x25 events output, refer to the Debug Command Reference document.
|
Excess Serial Errors on X.25 Link
The output of the show interfaces serial 0 privileged EXEC command shows rejects (REJs), receiver not ready events (RNRs), protocol frame errors (FRMRs), restarts (RESTARTs), or disconnects (DISCs) in excess of 0.5 percent of information frames (IFRAMEs).
Note If any of these fields is increasing and represents more than 0.5 percent of the number of IFRAMEs, there is likely a problem somewhere in the X.25 network. There should always be at least one SABM. However, if there are more than 10, the packet switch probably is not responding.
Table 9-28 outlines causes of this problem and describes possible solutions.
Table 9-28 No Connections over X.25 Link
Problem
|
Solution
|
Incorrect cabling or bad router hardware
|
•Check all cabling and hardware for damage or wear. Replace cabling or hardware as required. For more information on the Cisco 805 router and serial cables, refer to the Cisco 805 Router Hardware Installation Guide.
•Enter the show interfaces serial 0 privileged EXEC command to determine the status of the interface.
•If the interface is down, see the "Troubleshooting Serial Line Problems" section. If the interface is up but the line protocol is down, check the LAPB state in the output of the show interfaces serial 0 command.
•If the LAPB state is not CONNECT, use the debug lapb privileged EXEC command (or attach a serial analyzer) to look for SABMs being sent, and for UA packets being sent in reply to SABMs. If UAs are not being sent, one of the other possible problems described in this table is the likely cause.
•If the show interfaces serial 0 command indicates that the interface and line protocol are up but no connections can be made, there is probably a router or switch misconfiguration. Refer to the other possible problems outlined in this table.
|
Software Upgrade Methods
Following are the methods for upgrading software on Cisco 800 series and Cisco SOHO series routers:
•Copy the new software image to Flash memory over the LAN or WAN while the existing Cisco IOS software image is operating.
•Copy the new software image to Flash memory over the LAN while the boot image (ROM monitor) is operating.
•Copy the new software image over the console port while in ROM monitor mode.
•From the ROM monitor mode, boot the router from a software image that is loaded on a TFTP server. To use this method, the TFTP server must be on the same LAN as the router.
Recovering a Lost Password
This section describes how to recover a lost enable or enable secret password. The process of recovering a password consists of the following major steps:
1. Changing the Configuration Register
2. Resetting the Router
3. Resetting the Password and Saving Your Changes (for lost enable secret passwords only)
4. Resetting the Configuration Register Value
Note These procedures can be done only when you are connected to the router through the console port. These procedures cannot be performed through a Telnet session.
Note See the "Hot Tips" section on Cisco Connection Online (CCO) for additional information on replacing enable secret passwords.
Changing the Configuration Register
Follow these steps to change a configuration register.
Step 1 Connect an ASCII terminal or a PC running a terminal emulation program to the CONSOLE port on the rear panel of the router. Refer to the "Connecting the Router to a PC" section in the "Installation" chapter of the Cisco 827 Routers Hardware Installation Guide.
Step 2 Configure the terminal to operate at 9600 baud, 8 data bits, no parity, and 1 stop bit.
Step 3 At the privileged EXEC prompt (router_name >), enter the show version command to display the existing configuration register value :
Cisco Internetwork Operating System Software
IOS (tm) C827 Software (C827-NSY6-M), Version 12.0
Copyright (c) 1986-1999 by cisco Systems, Inc.
Compiled Mon 22-Nov-99 11:20 by dahsue
Image text-base:0x80013170, data-base:0x8081B748
ROM:System Bootstrap, Version 12.0(19990519:174856)
[jakumar-twister_dev 1055], DEVELOPMENT SOFTWARE
System returned to ROM by reload
CISCO C827 (MPC855T) processor (revision 0x00) with 19456K/1024K bytes
of memory.
Processor board ID 00000000, with hardware revision 0000
1 Ethernet/IEEE 802.3 interface(s)
1 ATM network interface(s)
128K bytes of non-volatile configuration memory.
16384K bytes of processor board System flash (Read/Write)
Configuration register is 0x100
Step 4 Record the setting of the configuration register. It is usually 0x2100 or 0x100.
Step 5 Record the break setting:
•Break enabled—bit 8 is set to 0.
•Break disabled (default setting)—bit 8 is set to 1.
Note To enable break, enter the config-register 0x01 command while in privileged EXEC mode.
Resetting the Router
Follow these steps to reset the router.
Step 1 If break is enabled, go to Step 2. If break is disabled, turn the router off ( O ), wait 5 seconds, and turn it on ( | ) again. Within 60 seconds, press the Break key. The terminal displays the ROM monitor prompt. Go to Step 3.
Note Some terminal keyboards have a key labeled Break. If your keyboard does not have a Break key, refer to the documentation that came with the terminal for instructions on how to send a break.
Step 2 Press Break. The terminal displays the following prompt:
Step 3 Enter confreg 0x142 to reset the configuration register:
Step 4 Initialize the router by entering the reset command:
The router cycles its power, and the configuration register is set to 0x142. The router uses the boot ROM system image, indicated by the system configuration dialog:
--- System Configuration Dialog ---
Step 5 Enter no in response to the prompts until the following message is displayed:
Press RETURN to get started!
Step 6 Press Return. The following prompt appears:
Step 7 Enter the enable command to enter enable mode. Configuration changes can be made only in enable mode:
The prompt changes to the privileged EXEC prompt:
Step 8 Enter the show startup-config command to display an enable password in the configuration file:
Router# show startup-config
If you are recovering an enable password, skip the following "Resetting the Password and Saving Your Changes" section, and complete the password recovery process by performing the steps in the "Resetting the Configuration Register Value" section.
If you are recovering an enable secret password, it is not displayed in the show startup-config command output. Complete the password-recovery process by performing the steps in the following "Resetting the Password and Saving Your Changes" section.
Resetting the Password and Saving Your Changes
Follow these steps to reset your password and save the changes.
Step 1 Enter the configure terminal command to enter configuration mode:
Router# configure terminal
Step 2 Enter the enable secret command to reset the enable secret password in the router:
Router(config)# enable secret password
Step 3 Enter exit to exit configuration mode:
Step 4 Save your configuration changes:
Router# copy running-config startup-config
Resetting the Configuration Register Value
After you have recovered or reconfigured a password, reset the configuration register value:
Step 1 Enter the configure terminal command to enter configuration mode:
Router# configure terminal
Step 2 Enter the configure register command and the original configuration register value that you recorded.
Router(config)# config-reg value
Step 3 Enter exit to exit configuration mode:
Note To return to the configuration being used before you recovered the lost enable password, do not save the configuration changes before rebooting the router.
Step 4 Reboot the router, and enter the recovered password.
Managing the Cisco Router Web Setup Tool
The Cisco Router Web Setup tool is a free software configuration utility, supporting the Cisco 800 series DSL routers, the Cisco 806 and 831 dual Ethernet routers, and the Cisco SOHO series routers. It includes a Web-based GUI that offers the following features:
•Simplified setup
•Advanced configuration
•Router security
•Router monitoring
Pointers to CRWS Documentation
To find the CRWS Introduction, go to:
http://www.cisco.com/go/CRWS
To see the CRWS Troubleshooting Guide, go to:
http://www.cisco.com/en/US/products/sw/netmgtsw/ps2076/prod_troubleshooting_guide09186a0080132c3c.html
