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cisco 3550 mac flapping issue

Hi experts

I have cisco 3550 switch with below configuration where I am getting below log message

Dec 16 12:07:19.547 IST: %SW_MATM-4-MACFLAP_NOTIF: Host 001a.2f84.d73f in vlan 66 is flapping between port Fa0/6 and port Fa0/15

this config is for load sharing between two ports


interface FastEthernet0/6
switchport access vlan 66
switchport mode access
load-interval 30


interface FastEthernet0/15
switchport access vlan 66
switchport mode access
load-interval 30

Please let me know the solution

Comments
Community Member

Hi Mahesh

This can happen if both the service NICs are in active/active, and the switch bringing up the ARP of port is active at that point of time.. this can actually cause too many spanning tree TCNs on the network and once I saw the switch cpu going to 99 % due to this.. to avoid this you can do the following:

1) configure the server NICs in active/passive mode, which will make sure that the MAC is learnt from a single port

2) if your server supports etherchannels or bundles, you can bundle the two ports and make it look like one port on the switch side. spanning tree would then be enabled on the bundle and not on individual switch ports...

hope this helps..all the best..

Raj

Community Member

Ok,

Now topology is two fe link from this 3550 switch is connected to other 4507 switch

3550======two fe link=======4507

when tried etherchannel traffic from 3550 goes to only one link towards 4507 due to limitation of 3550 (load balance either on src-mac ot dst-mac)

Now at 3550 config is same as pasted in first query and at 4507 etherchannel is configured. I have tried to load balance to link by calling same vlan on two ports

is there any other way to bundle two port ?

regards

Hi Mahesh

The configs given in your previous post doesnt really involve configuring etherchannels.. It just has access ports configured, and it wouldnt load balance with that config... You need to have "channel-group 1 mode desirable
" configured on the access ports, and have the portchannel configured.. Have a look at this URL.. this has an example of how to bundle ports between 3550 & 6500...

http://www.cisco.com/en/US/tech/tk389/tk213/technologies_configuration_example09186a0080094647.shtml

Hope this helps.. all the best..


Raj

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