System information

Troubleshooting ISDN
Book Title
17-394
dialer fast-idle time too high Step 1 Use the show running-config privileged exec command to view the router
configuration. Check for a dialer fast-idle interface configuration
command entry.
This command does not appear in the configuration unless it has been
changed from the default.
Syntax:
dialer fast-idle seconds
The fast-idle timer is activated if there is contention for
a line. In other words, if a line is in use and a packet for a different next
hop address is received, and the busy line is required to send the
competing packet, the dialer fast-idle timer is activated.
Step 2 Check the value specified by the dialer fast-idle command. If there is
contention for an ISDN line but an idle connection does not disconnect
quickly enough, the value is probably set too high.
Step 3 Decrease the value specified by the dialer fast-idle command. This forces
idle connections to disconnect more quickly when there is contention for
the line.
Dialer list access-list
commands not restrictive
enough
Step 1 Use the show access-list privileged exec command to see the access lists
configured on the router. Access lists determine which packets cause
dialing to occur and which packets reset the idle-timer, keeping the
connection up.
Step 2 Use the show running-config privileged exec command to view the router
configuration. Check which access lists are applied to the interface with
dialer-list commands.
Syntax:
dialer-list dialer-group protocol protocol {permit | deny | list
access-list-number}
This command creates a list that defines what traffic is interesting enough
to initiate and sustain an ISDN call for an interface that belongs to the
same dialer-group number.
Step 3 Examine the specified access lists to make sure the line is not being kept
up for uninteresting traffic. The access lists need to be more restrictive if
the line never goes down.
In particular, make sure that routing updates or SNMP
1
packets do not
reset the idle timer or bring the line up.
Step 4 If necessary, modify access lists to restrict uninteresting traffic.
1 SNMP = Simple Network Management Protocol
Possible Problem Solution