System information

Troubleshooting ISDN
Book Title
17-386
ISDN: No Communication with Remote Router
Symptom: ISDN connection attempts are successful, but attempts to ping or otherwise
communicate with the remote ISDN router interface fail.
Table 17-4 outlines the problems that might cause this symptom and describes solutions to those
problems.
Table 17-4 ISDN: No Communication with Remote Router
Possible Problem Solution
CHAP
1
misconfigured Step 1 Use the debug ppp chap privileged exec command.
Step 2 Try to ping the remote router. Look for the message “Passed chap
authentication.”
Step 3 If you do not see this message, use the show running-config
privileged exec command to view the router configuration. Make
sure that the ppp authentication chap interface configuration
command is configured on both the local and remote routers.
Syntax:
ppp authentication {chap | chap pap | pap chap | pap}
[if-needed] [list-name | default] [callin][one-time]
• chap—Enables CHAP on a serial interface.
• pap—Enables PAP
2
on a serial interface.
• chap pap—Enables both CHAP and PAP, and performs CHAP
authentication before PAP.
• pap chap—Enables both CHAP and PAP, and performs PAP
authentication before CHAP.
• if-needed—(Optional) Used with TACACS
3
and extended
TACACS. Does not perform CHAP or PAP authentication if the
user has already provided authentication. This option is available
only on asynchronous interfaces.
CHAP misconfigured • list-name—(Optional) Used with AAA
4
. Specifies the name of a
list of methods of authentication to use. If no list name is
specified, the system uses the default. The list is created with the
aaa authentication ppp command.
• default—The name of the method list is created with the aaa
authentication ppp command.
• callin—Specifies authentication on incoming (received) calls
only.
• one-time—(Optional) Accepts the username and password in the
username field.
Step 4 Check username global configuration command entries. Make sure
that username statements use the host name of the remote router.
Make sure that the passwords on both the local and remote router are
identical. Use the username command to add or alter username
entries. For more information, refer to the Cisco IOS configuration
guides and command references.