System information

Troubleshooting ISDN Connections 17-395

ISDN: Line Disconnects Too Quickly

Symptom: ISDN connections are successfully established, but connections disconnect too quickly

when idle.

Table 17-11 outlines the problems that might cause this symptom and describes solutions to those

problems.

Table 17-11 ISDN: Line Disconnects Too Quickly

Possible Problem Solution

Misconﬁgured

dialer idle-timeout

command

Step 1 Use the show running-conﬁg privileged exec command to view the router

conﬁguration. Check for a dialer idle-timeout interface conﬁguration

command entry.

If the command is not present on the interface, the interface uses the default of

120 seconds.

Step 2 Check the value speciﬁed by this command. If the ISDN line disconnects too

quickly when idle, the value is probably set too low.

Step 3 Increase the value speciﬁed by the dialer idle-timeout command. This allows

connections to stay idle longer before disconnecting.

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.

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.

This command does not appear in the conﬁguration unless it has been changed

from the default of 20 seconds.

Step 2 Check the value speciﬁed by this command. If there is contention for an ISDN

line and the line disconnects too quickly, the value is probably set too low.

Step 3 Increase the value speciﬁed by the dialer fast-idle command. This allows idle

connections to stay connected longer when there is contention for the line.