%C4K_EBM-4-HOSTFLAPPING: Host 86:AA:C0:79:AA:6A in vlan 60 is flapping between port Gi5/9 and port Gi5/23

[sachin_sharma0021]

%C4K_EBM-4-HOSTFLAPPING: Host 86:EE:E0:79:AF:6D in vlan 60 is flapping between port Gi5/9 and port Gi5/23.

  Please suggest me how can i fixed it ?

[Latchum Naidu]

Hi,

It sounds like you have a loop in your network. This can be caused by different things including someone adding a hub or switch to your network somewhere. If you aren't running spanning-tree, turn it on. If you are running spanning-tree and this is still happening, the rogue switch/hub is connecting 2 ports that are in different vlans.

see the below link for more information
http://www.cisco.com/en/US/products/hw/switches/ps4324/products_tech_note09186a008063c36f.shtml

Trace what equipment connects to the port Gi5/9 & Gi5/23, and go check it.

When you shut down a port, the device attached to it should go offline, too. If nothing goes offline, it must have a secondary route to the network.

One suspect might be a laptop with Wi-fi being plugged into a hardwire connection, with "Internet Connection Sharing" enabled. That might be the rogue. It would be intermittent if the laptop is taken from the desk and carried around by the user when away from their usual workplace, using only the wi-fi at those times. It would then reappear when the user returned and plugged in the hardwire again.

Please rate the helpfull posts.
Regards,
Naidu.

[sachin_sharma0021]

Hello Naidu,

On ports Gi 5/9 & Gi 5/23 STP Port fast is enabled. So please confirm this could be the cause of that problem ?

[nkarpysh]

It is not because of portfast in particular - it is because of the loop behind those portfast ports - find what is connected there and see if that can be fixed.

Nik

[nkarpysh]

Hello,

Message means that packets with same source MAC address coming from two different interface. That means you may have a netwrok loop causing this. You need to go to devices connected to interfaces Gi5/9 and Gi5/23 and check where this MAC is learnt on those. And trace it further same way checking the STP details.

By this you will find a loop to fix it. Most common cause is High CPU on one f the switches in the way or uni-directional link causing STP problems.

Nik

[glen.grant]

  Als do a show cdp neighbor and see if the switch sees itself on those 2 ports , if so then those 2 ports are somehow physically tied together and must be fixed ,  spanning tree won't always fix this situation though it should.