You want to enable HSRP SNMP traps.
Cisco has developed an HSRP SNMP MIB to help manage routers using this feature. You can configure your router to send an SNMP trap every time the routers make an HSRP state change:
Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#snmp-server enable traps hsrp Router1(config)#snmp-server host 172.25.1.1 ORATRAP Router1(config)#end Router1#
Usually when a router changes its HSRP state, this indicates that some sort of network problem has occurred. If you are tracking interfaces as in Recipe 22.3, then the problem may be that the WAN interface on the primary router has failed. In this case, you will almost certainly also receive a Link-Down trap from the primary router, as well as a trap indicating that the primary has become inactive and the secondary router has become active.
In some cases, it can be extremely useful to receive these traps. For example, the primary router's power supplies may have suddenly failed. In this case, the first indication you may get that there has been a problem will be the next time your network management system tries to poll the primary router. Clearly, there are cases when you want to know about the change sooner than that. So having the secondary router to send a trap to indicate the change of HSRP state may be the fastest way to get this information.
These traps can also be useful if there is something wrong with your HSRP setup, so that the two routers are continually flipping back and forth between active and standby states. As long as the traffic continues to flow, you may not otherwise know that there is a problem. This could happen, for example, if you set the HSRP timers improperly.
Cisco's HSRP MIB also allows you to use SNMP to query the routers for their current HSRP state information. Please refer to Chapter 17 for more information about using SNMP.
Recipe 22.3; Recipe 22.6; Chapter 17