it may not be obvious without this information which router is the standby router. One important aspect of HSRP that many people miss is that if more than two rout- ers are participating, once an election for active and standby routers has completed, the remaining routers are neither active nor standby until the standby router becomes active. RFC 2281 states: To minimize network traffic, only the active and the standby routers send periodic HSRP messages once the protocol has completed the election process. If the active router fails, the standby router takes over as the active router. If the standby router fails or becomes the active router, another router is elected as the standby router. HSRP Interface Tracking While HSRP is a wonderful solution that enables recovery from router or Ethernet interface failures, its basic functionality falls short in another scenario. Figure 13-3 depicts a more complex problem than the one considered previously. In this scenario, the serial link connecting Router A to the Internet has failed. Because the router and Ethernet interfaces are still up, HSRP is still able to send and receive hello packets, and Router A remains the active router. Chapter 13: Resilient Ethernet Internet Router A Router B Ethernet - 192.168.100.0/24 Figure 13-3. Primary Internet link failure without interface tracking The network is resilient, SO the packets will still get to the Internet via the F0/1 interfaces-but why add another hop when we don't need to? If we could somehow influence the HSRP priority based on the status of another interface, we could fail the VIP from Router A over to Router B based on the status of SO/O. HSRP interface tracking allows us to do exactly that. By adding a couple of simple commands to our HSRP configurations, we can create a design that will allow the Ethernet interfaces to failover in the result of a serial interface failure: Router A: interface fo/o ip address 192.168.100.2 255.255.255.0 standby ip 192.168.100.1 standby preempt standby track Serialo/o 10 Router B: i