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packet drop and latency on LAN

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.


Hall of Fame Super Blue

Re: packet drop and latency on LAN

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 ?


Community Member

Re: packet drop and latency on LAN

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


Re: packet drop and latency on LAN


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



Community Member

Re: packet drop and latency on LAN

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.


Community Member

Re: packet drop and latency on LAN

hi sai,

try to figure out any wireless access

provided which may lead to host flapping

an possibility

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