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Chapter 9      Troubleshooting
Troubleshooting Serial Line Problems
Modem Cannot Send or Receive IP Data
After a dial-up connection is established, a modem cannot send or receive IP data.
Ta b l e 9 - 1 9 outlines causes of this problem and describes possible solutions. 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...

 
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Table 9-19 Modem Cannot Send or Receive IP Data
Problem Solution
IP routing not enabled on 
local or remote routerMake 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...

 
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Chapter 9      Troubleshooting
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Modem Does Not Disconnect Properly
The modem does not disconnect properly. Connections to the modem do not 
terminate when the quit command is entered.
Ta b l e 9 - 2 0 outlines causes of this problem and describes possible solutions. Static routes not 
configured
Use the show ip route privileged EXEC command to check whether 
there is a static route to the remote network...

 
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Link Deactivates Too Quickly
After a dial-up connection is established, the link deactivates too quickly.
Ta b l e 9 - 2 1 outlines causes of this problem and describes possible solutions.
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.
Ta b l e 9 -...

 
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Chapter 9      Troubleshooting
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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.
Ta b l e 9 - 2 3 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...

 
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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...

 
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Chapter 9      Troubleshooting
Troubleshooting Serial Line Problems
Frame Relay Problems
This section describes how to troubleshoot the following Frame Relay symptoms:
Frame Relay Link Is Down, page 9-45
Cannot Ping Remote Router, page 9-48
Cannot Ping End to End, page 9-51
Frame Relay Link Is Down
Connections over a Frame Relay link fail. Ta b l e 9 - 2 4 outlines causes of this 
problem and describes possible solutions.
Table 9-24 Frame...

 
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Local management interface 
(LMI) type mismatchUse 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...

 
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Cannot Ping Remote Router
Attempts to ping the remote router across a Frame Relay connection fail. 
Ta b l e 9 - 2 5 outlines causes of this problem and describes possible solutions. 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...

 
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DLCI inactive or deletedEnter 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...