I talked briefly about how you can track interfaces with HSRP during my last posting. Consider the following diagram:Imagine PE 1 and 2 are in a standard HSRP configuration. PE1 is the active router, and the main route out of the network is out of Ethernet2 to the central router. However, if this interface were to go down for any reason, we want the priority of PE1 to go below that of PE2, so that PE2 takes over and can route to that central router. Interface tracking is a prime solution for this dilema. The config would be as follows:
(config-if)standby [group #] track ethernet2 [decrement value] - if PE1 is 120, and PE2 is the default value of 100, than we will need the decrement to be greater than 20. The default is 10.
(config-if)standby [group #] preempt - most people forget this command, but it must be entered for PE2 to take over when PE1's priority drops below its own.
Verify the decrement and tracking with the show standby command.
To debug HSRP use the debug standby command (go figure...standby again)