Symptom
the packet with special Destination Mac address doesn't be dropped by STP block port of C2960X and then it will cause loop and storm.
Conditions
The packet with special Destination Mac address.
Affects the following Cisco IOS XE Software versions:
+--------------------------------------------------------+
| Major Release | Affected Release | First Fixed Release |
|---------------+------------------+---------------------|
| 15.0SE | 15.0(2)SE8 | 15.0(2)SE9 |
|---------------+------------------+---------------------|
| | 15.2(2)E1 | |
| | 15.2(2a)E1 | |
| | 15.2(2)E2 | 15.2(2)E3 |
| 15.2E | 15.2(3)E | 15.2(3)E2 |
| | 15.2(3a)E | 15.2(3)E3 |
| | 15.2(3)E1 | |
| | 15.2(3)E2a | |
+--------------------------------------------------------+
Affects most Cisco Catalyst 2k and 3k switches. These include 3750, 3750X, 3750E, 2960S, 2960S etc.
Workaround
enabling "dot1x system-auth-control" in global config mode, may help mitigate depending on the L2 frame that is being flooded.
Further Problem Description
this packet is not dropped on STP FWD port neither
