Core Issue
Hot Standby Router Protocol (HSRP) changes its state when it fails to receive three consecutive HSRP hello packets from its peer.
The most common issues are physical layer problems or excessive network traffic, which are caused by Spanning-Tree Protocol (STP) problems.
Resolution
To determine if HSRP packets are being sent and received correctly, issue the debug standby command.
For more information, refer to the Layer 3 HSRP Debugging section of Understanding and Troubleshooting HSRP Problems in Catalyst Switch Networks.
