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Error Message Ports Flapping on Cisco 3750 Stack

     I am receiving the following error message on a Cisco 3750 switch stack.  Any suggestions for troubleshooting this error message.

Thanks, David

00:03:13: %SW_MATM-4-MACFLAP_NOTIF: Host 00d0.7400.2730 in vlan 600 is flapping between port Gi2/0/3 and port Gi2/0/2             

Everyone's tags (2)

Error Message Ports Flapping on Cisco 3750 Stack

Hi, i googled around a bit about this and this is what i found: 

is this a server with dual nic's that is load balancing over its nics?

if so, the trick is to disable load balancing on the server and rather configure the dual nics for fail-over.

Error Message Ports Flapping on Cisco 3750 Stack


Check also for any STP loop

VIP Purple

Error Message Ports Flapping on Cisco 3750 Stack

HI David,

There are lots of thread discussing about this,

Anyway, this is how you approach these types of flapping:

1. Is the the given MAC flapping in the log flapping only 1 time or you see it multiple times over a reasonobly short time?

  If you see it only once or once every 2-3 hours this might be not an issue worth being investigated. Sporadic one time flapping are expected in L2 broadcast domain.

If you see it often continue to step 2.

2. Identify and locate the flapping mac in vlan 600: 00d0.7400.2730

the mac of a dual-homes server using some kind of load balancing algorithm (active/active) for which the same address is used from both NICs?

If yes, the message is not and issue but just an indication. Fix this type of LB (make it active/standby or make sure the server uses 2 different mac addresses, one per NIC) or if it is not possible leave it like this.

3. Is the MAC a the wireless NIC of a PC?

Make sure that the user was not moving from one AP to another (flapping is normal in this case)

4. If all previous answers are no start checking STP in vlan 600. Do you see an increasing number of TCNs  > type

show spanning-tree vlan 600 detail MULTIPLE TIMES and look for  topology changes number

VLANxxxx is executing the rstp compatible Spanning Tree protocol

  Bridge Identifier has priority 32768, sysid 5, address 0024.5043.c700

  Configured hello time 2, max age 20, forward delay 15, transmit hold-count 6

  We are the root of the spanning tree

  Topology change flag not set, detected flag not set

  Number of topology changes 1 last change occurred 3w0d ago   <<<<<<<

          from GigabitEthernet1/0/1          <<<<<<

  Times:  hold 1, topology change 35, notification 2

          hello 2, max age 20, forward delay 15

  Timers: hello 0, topology change 0, notification 0, aging 300

See if you have increasing TCN's and check if they are coming from the same interface.

From this point on you keep on troubleshooting STP until you find the offending link (likely going up and down) or the switch. You also need to check if STP in vlan 600 is coherent with the actual L2 topology you have.


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