Troubleshooting ISDN Connections - Internetworking Troubleshooting - page 501

Table17-5 Dialup Receiving Modem Does Not Disconnect Properly

Possible Causes Suggested Actions

Modem is not
sensing DTR

Enter the Hangup DTR modem command string. This command
tells the modem to drop the carrier when the DTR signal is no
longer being received.
On a Hayes-compatible modem, the &D3 string is commonly
used to configure Hangup DTR on the modem. For the exact
syntax of this command, see the documentation for your modem.

Modem control is
not enabled on
the router or
access server

1.

Use the show line exec command on the access server or
router. The output for the auxiliary port should show inout or
RIisCD in the Modem column. This indicates that modem
control is enabled on the line of the access server or router.

2.

Configure the line for modem control using the modem inout
line configuration command. Modem control is now enabled
on the access server.

Modem control is
not enabled on
the router or
access server
(continued)

Note: Be certain to use the modem inout command instead of the
modem dialin command while the connectivity of the modem is
in question. The latter command allows the line to accept
incoming calls only. Outgoing calls will be refused, making it
impossible to establish a Telnet session with the modem to
configure it. If you want to enable the modem dialin command,
do so only after you are certain that the modem is functioning
correctly.

Troubleshooting Outbound Calls

The troubleshooting approach for incoming calls starts at the bottom, but troubleshooting an outbound
connection starts at the top. Outbound connection troubleshooting goes along these lines (a “yes” answer
to the question gets to the next question):
•

Does dial-on-demand routing initiate a call?

•

If this is an async modem, do the chat scripts issue the expected commands?

•

Does the call make it out to the PSTN?

•

Does the remote end answer the call?

•

Does the call complete?

•

Is data passing over the link?

•

Is the session established? (PPP or terminal)

Verifying Dialer Operation

To see whether the dialer is trying to make a call to its remote destination, use the command debug
dialer events . More detailed information can be gained from debug dialer packet , but the debug dialer
packet command is resource-intensive and should not be used on a busy system that has multiple dialer
interfaces operating.