System information

Troubleshooting Dialin Connections
Book Title
16-352
Dialin: Modem Does Not Answer
Symptom: When attempting to open a dialin connection to a modem, the modem does not answer
the call.
Table 16-4 outlines the problems that might cause this symptom and describes solutions to those
problems.
Table 16-4 Dialin: Modem Does Not Answer
Possible Causes Suggested Actions
Incorrect cabling
Step 1 Check the cabling between the modem and the access server or
router. Confirm that the modem is connected to the auxiliary port on
the access server or router with a rolled RJ-45 cable and an MMOD
DB-25 adapter. This cabling configuration is recommended and
supported by Cisco for RJ-45 ports. (These connectors are typically
labeled “Modem.”)
There are two types of RJ-45 cabling: straight and rolled. If you hold
the two ends of an RJ-45 cable side-by-side, you’ll see eight colored
strips, or pins, at each end. If the order of the colored pins is the same
at each end, then the cable is straight. If the order of the colors is
reversed at each end, then the cable is rolled.
The rolled cable (CAB-500RJ) is standard with Cisco’s 2500/CS500.
Step 2 Use the show line exec command to verify that the cabling is correct.
See the explanation of the show line command output in the section
“Using debug Commands” earlier in this chapter.
Modem control not enabled on
access server or router
Step 1 Observe the remote modem to see whether it is receiving a DTR
signal from the router. Most modems have a DTR indicator light.
Check the modem documentation to interpret the indicator lights.
Step 2 If the DTR indicator light is on, the modem is seeing a DTR signal
from the router. You can also enter the show line exec command to
check for DTR. If the modem hardware state shows the string
noDTR, then the router is configured to hold DTR low and the
modem is not seeing a DTR signal.
Step 3 Configure modem control using either the modem inout or the
modem ri-is-cd line configuration command.
Misconfigured dialer map
commands
Step 1 Use the show running-config privileged exec command to view the
router configuration. Check all dialer map statements to make sure
they are configured correctly.
Step 2 Correct dialer map statements as necessary, making certain that all
options are specified properly.
For detailed information on configuring dialer maps, refer to the Cisco IOS
Wide-Area Networking Configuration Guide and Wide-Area Networking
Command Reference.
Remote modem not set to
auto-answer
Step 1 Check the remote modem to see whether it is set to auto-answer.
Usually, an AA indicator light is on when auto-answer is set.
Step 2 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.