MAC address flapping on 2 x Cisco 3750 (Stacked)

Unanswered Question
Feb 2nd, 2010

Hi All,

I am having some issue with my connectivity.

The setup with HP virtual connect (VC) is as below:

Server A NIC 1 -- VC 1 -- Switch A

             NIC 2 -- VC 2 -- Switch A
Server B NIC 1 -- VC 1 -- Switch A
             NIC 2 -- VC 2 -- Switch A

The VLAN configuration are done on individual NIC card on the servers and the switchport on Switch A facing the VC connect are all on trunk mode.

Currently I am seeing MAC address flapping on my Switch. The switches are CISCO 3750 and are being stacked so it appears logically as 1 switch.

Any idea what might be the problem?

Below is an output of the flapping on the switch.

%SW_MATM-4-MACFLAP_NOTIF: Host xxxx.xxxx.0637 in vlan 1 is flapping between port Gi2/0/3 and port Gi2/0/5

%SW_MATM-4-MACFLAP_NOTIF: Host xxxx.xxxx.46eb in vlan 1 is flapping between port Gi1/0/5 and port Gi1/0/7

%SW_MATM-4-MACFLAP_NOTIF: Host xxxx.xxxx.661d  in vlan 1 is flapping between port Gi2/0/15 and port Gi2/0/7

I have this problem too.
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Ganesh Hariharan Tue, 02/02/2010 - 09:22

Hi,

Problem of MAC FLAP could resolve by following methods:.


Check with the server providers to see if the OS and server platform support 'NIC' Teaming (NIC Bonding).

FYI - NIC teaming allows users to group two or more physical NICs into a single logical network device called a bond. Once a logical NIC is configured, the virtual machine is not aware of the underlying physical NICs. Packets sent to the logical NIC are dispatched to one of the physical NICs in the bond and packets arriving at any of the physical NICs are automatically directed to the appropriate logical NIC. If one of the underlying physical NICs is broken or its cable has been unplugged, server will detect the fault condition and automatically move traffic to another NIC in the bond.

Hope that help

If helpful do rate

Ganesh.H

noobieee7 Tue, 02/02/2010 - 18:08

Hi Ganesh,

I manage to find out that the mac address that are causing the flaps, are from the stacking cable between the 2 virtual connects.

billwesselman Fri, 10/08/2010 - 00:31

I have 3 "bonded" (2 NICs each, bonded into a single virtual device on each server) servers.  My Cisco 3750 switch is giving

"SW_MATM-4-MACFLAP_NOTIF: Host 000c.2923.8472 in vlan 1 is flapping between port Gi1/0/2 and port Gi1/0/1"

with identical (except for Host and port #'s) errors for each servers pair of ports on the switch.

What do I need to do to the switch to get it to recognize that each port pair is for a single servers bonded NIC pair?

Is it sufficient to configure each pair of interfaces with the same name and ip addresses (each server has multiple virtual machines, each with at least 1 ip address)?

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