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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 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. 
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 modems 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. 
						

							 
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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 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.
Table 9-12 Modem Does Not Dial (continued)
Problem Solution 
						

							 
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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
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. 
						

							 
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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 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. 
						

							 
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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 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.
Table 9-14 Modem Hangs Up Shortly After Connecting (continued)
Problem Solution 
						

							 
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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 Solution
Autoselect is enabled on 
the lineTry 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.  
						

							 
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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 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.
Table 9-15 Dial-Up Client Receives No EXEC Prompt (continued)
Problem Solution 
						

							 
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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 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. 
						

							 
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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 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. 
						

							 
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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 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.