Data traffic is flooding
Data is not getting forwarded, instead it is being flooded to all ports of a VLAN.
Possible Cause
MAC address learning is disabled because of loop detection. A severity 2 syslog message, STM_LOOP_DETECT, should have been received.
Solution
After waiting for 180 seconds, learning is enabled automatically. A severity 2 syslog message, STM_LEARNING_RE_ENABLE, should be received.
Possible Cause
The MAC address table is full. A severity 2 syslog message, STM_LIMIT_REACHED, should have been received.
Solution
After waiting for 180 seconds, the MAC table is flushed and learning is enabled automatically.
Alternatively, wait until some MAC entries are aged out, so that the total learned entries fall below 1500, or enter the clear mac address-table dynamic [address <mac> ] command to clear out entries. This creates free space for new MAC entries to be learned. A severity 2 syslog message, STM_LEARNING_RE_ENABLE, should be received.
Possible Cause
MAC address learning is disabled due to a learning overload (that is, too many new addresses in a short time). A severity 4 syslog message, STM_LEARNING_OVERLOAD, should have been received.
Solution
After waiting for 120 seconds, learning is enabled automatically.
MAC address not learned
MAC address is not learned by the switch. This causes the MAC address not to be listed in the MAC table.
Possible Cause
MAC address learning is disabled because of loop detection. A severity 2 syslog message, STM_LOOP_DETECT, should have been received.
Solution
After waiting for 180 seconds, learning is enabled automatically. A severity 2 syslog message, STM_LEARNING_RE_ENABLE, should be received.
Possible Cause
The MAC address table is full. A severity 2 syslog message, STM_LIMIT_REACHED, should have been received.
Solution
After waiting for 180 seconds, the MAC table is flushed and learning is enabled automatically.
Alternatively, wait until some MAC entries are aged out, so that the total learned entries fall below 1500, or enter the clear mac address-table dynamic [address <mac> ] command to clear out entries. This creates free space for new MAC entries to be learned. A severity 2 syslog message, STM_LEARNING_RE_ENABLE, should be received.
Possible Cause
MAC address learning is disabled due to a learning overload (that is, too many new addresses in a short time). A severity 4 syslog message, STM_LEARNING_OVERLOAD, should have been received.
Solution
After waiting for 120 seconds, learning is enabled automatically.
Possible Cause
No egress path was set for the incoming data traffic. The MAC address from a data stream is not learned if there is no path for that data going out of the switch.
Solution
Configure an outgoing path for the data.
For example, the VLAN may not have been enabled on any of the interfaces other than the one on which data is coming in on. Alternatively, the outgoing interfaces may be down. If this is the case, you need to bring up those interfaces.
Traffic flooding in a VPC setup
Data is not getting forwarded, instead it is being flooded in the presence of a VPC scenario.
Possible Cause
The MAC address is learned on one switch only. Typically, this situation would be a bug regarding the synchronization of the MAC address with the VPC peer.
Solution
Clear the MAC address from the switch where it was learned. This triggers new learning and synchronization of the MAC addresses across the VPC switches.