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Chapter 9      Troubleshooting
Troubleshooting Serial Line Problems
Modem Does Not Dial
Dial-up sessions cannot be established because the modem does not dial properly.
Ta b l e 9 - 1 2 outlines the problems that might cause this symptom and describes 
solutions to those problems.
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...

 
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Modem Does Not Answer
When attempting to open a dial-up connection to a modem, the modem does not 
answer the call. 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...

 
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Ta b l e 9 - 1 3 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...

 
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Modem Hangs Up Shortly After Connecting
A dial-up connection is successful but the modem hangs up after 30 to 
90 seconds.
Ta b l e 9 - 1 4 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...

 
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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...

 
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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).
Ta b l e 9 - 1 5 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...

 
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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.
Ta b l e 9 - 1 6 outlines causes of this problem and describes possible solutions. Modem speed setting is not 
locked.
Enter the...

 
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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).
Ta b l e 9 - 1 7 outlines causes of this problems and...

 
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Modem Cannot Send or Receive Data
After a dial-up connection is established, a modem cannot send or receive data of 
any kind.
Ta b l e 9 - 1 8 outlines causes of this problem 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...

 
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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...