As stated from cisco's website:
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Case Study #1: HSRP Standby IP Address Is Being Reported As a Duplicate IP Address
Sample error message:
Oct 12 13:15:41: %STANDBY-3-DUPADDR: Duplicate address 10.25.0.1
on Vlan25, sourced by 0000.0c07.ac19
Oct 13 16:25:41: %STANDBY-3-DUPADDR: Duplicate address 10.25.0.1
on Vlan25, sourced by 0000.0c07.ac19
Oct 15 22:31:02: %STANDBY-3-DUPADDR: Duplicate address 10.25.0.1
on Vlan25, sourced by 0000.0c07.ac19
Oct 15 22:41:01: %STANDBY-3-DUPADDR: Duplicate address 10.25.0.1
on Vlan25, sourced by 0000.0c07.ac19
These error messages do not necessarily indicate an HSRP problem. Rather, the error messages indicate a possible Spanning-Tree Protocol (STP) loop or router/switch configuration issue. The error messages are just symptoms of another problem.
In addition, these error messages do not prevent HSRP from operating correctly. The duplicate HSRP packet is ignored. These error messages are throttled at 30 second intervals. However, network slow performance and packet loss may result from the network instability that is causing the STANDBY-3-DUPADDR error messages of the HSRP address.
Sample error message:
Oct 15 22:41:01: %STANDBY-3-DUPADDR: Duplicate address 10.25.0.1
on Vlan25, sourced by 0000.0c07.ac19
Specifically, the above messages indicate that the router received a data packet sourced from the HSRP IP address on VLAN25 with the MAC addresses 0000.0c07.ac19. Since the HSRP MAC address is 0000.0c07.ac19, either the router in question received its own packet back or both routers in the HSRP group went into the active state. Since the router received its own packet, the problem most likely is with the network rather than the router. A variety of problems can cause this behavior. Momentary STP loops, EtherChannel configuration issues, and duplicated frames are examples of possible network problems that can cause the STANDBY-3-DUPADDR error messages.
When troubleshooting these error messages, review the troubleshooting steps outlined in the HSRP Troubleshooting Modules section of this document. All of the troubleshooting modules are applicable to this section, including modules on configuration. In addition, note any errors in the switch log and reference additional case studies as necessary.
Furthermore, there is a method to prevent the active router from receiving its own multicast hello packet by using an access-list. However, this is only a work-around for the error messages. This work-around actually hides the symptom of the problem. The work-around is to apply an extended inbound access-list to the HSRP interfaces blocking all traffic sourced from the physical IP address destined to all routers multicast address 224.0.0.2. For example:
access-list 101 deny ip host 172.16.12.3 host 224.0.0.2
access-list 101 permit ip any any
interface ethernet 0
ip address 172.16.12.3 255.255.255.0
standby 1 ip 172.16.12.1
ip access-group 101 in
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