Core Issue
The most common reason for this problem is that the Hot Standby Router Protocol (HSRP) hello packets are not being permitted through the Access Control List (ACL).
Resolution
Permit the destination address of the HSRP hello packet 224.0.0.2. The router's primary IP address is the source address. A sample ACL command follows:
access-list 101 permit ip host <source-address> host 224.0.0.2
For more information on HSRP, refer to Hot Standby Router Protocol Features and Functionality
Source
Multiple devices
Source and Destination Physical Connectivity
Source and destination exist on same subnetwork
