packet drop and latency on LAN

Unanswered Question
Mar 18th, 2008

we are seeing thie particular error message on our core and dist switch

%C4K_EBM-4-HOSTFLAPPING: Host 02:01:00:00:00:00 in vlan 101 is flapping between port Gi1/3 and port Gi1/45

Has anyone faces this before?

I got to know that the MAC is used by the Win server for load balancing.


I have this problem too.
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Jon Marshall Tue, 03/18/2008 - 01:14

Hi Sai

The %C4K_EBM-4-HOSTFLAPPING:Host [mac-addr] in vlan [dec] is flapping between port [char] and port [char] error message appears.

This error message appears on the switch when the switch detects the specified host address as a source address on multiple ports.

Basically the switch is seeing the same mac-address on 2 different ports. How are the NIC's on the W2k server set up ?


saimbt Tue, 03/18/2008 - 01:20

this are happening on ports connected to desktops running the Wins 2003 server OS.


royalblues Tue, 03/18/2008 - 01:29


If the server is running the network loadbalancing service, you will get this message.

You can uninstall this service if this is not required

If you have done this for throughput, i would prefer doing LACP etherchannel which mostly works better than the MS loadbalancing



saimbt Tue, 03/18/2008 - 03:38

In this case the MAC address was 02:01:00:00:00:00

The mac address in question is used by Windows 2003 Server with Network Load Balancing.

As multiple desktops had enabled the load balancing feature, the MAC 02:01:00:00:00:00 got flooded throughout the network and gave rise to a STP loop.

To solve this, we found the ports with machines having the “network load balancing” feature enabled and manually shut those ports.


shiva_ial Tue, 03/18/2008 - 03:48

hi sai,

try to figure out any wireless access

provided which may lead to host flapping

an possibility


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