Hot Standby Router Protocol (HSRP) provides transparent first hop redundancy for end hosts in IP networks.
If the tracked interface fails, track the state of another interface on the router and lower the HSRP priority of the group by configuring the HSRP active router with the standby track command.
This allows another HSRP router configured with a higher priority and the standby preempt command to take over the role of the active router immediately.
If the new HSRP active router has a BRI interface configured to treat the received LAN traffic as interesting, the ISDN link is triggered.
The triggering of the ISDN link after HSRP failover does not imply the existence of a fault by itself.
HSRP is not configurable on WAN interfaces and HSRP by itself does not trigger the ISDN link. The ISDN link gets triggered if the HSRP active router routes traffic to the BRI interface and this traffic is defined as interesting by issuing the dialer-list command.
For information on HSRP, refer to Hot Standby Router Protocol Features and Functionality.
For information on HSRP preempt and track, refer to How to Use the standby preempt and standby track Commands.