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Cisco Bug: CSCsz28116 - Shared HSRP MAC address on subinterfaces can cause HSRP flapping

Last Modified

Aug 10, 2017

Products (1)

  • Cisco IOS

Known Affected Releases

12.2(33)SRD4a 12.2SG 12.2SR 12.2SY 12.2XN 12.4T

Description (partial)


On some platforms this problem represents an inefficiency in the operation of maintaining a shared MAC address on an interface, this is because the MAC address filter is reprogrammed with the same MAC that had just previously been removed. On a few platforms, the reprogramming of the MAC address filter for an identical address results in a full interface RESET. This causes the interface LINK state to flap that in turn results in instability in HSRP operation, and a continuous flapping of state.


The problem occurs in configurations in which the same group number, is shared between sub-interfaces of the same main interface. An example might be, dot1q interfaces with the same group number that are a child of a main Gigabit Ethernet interface.
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