Unanswered Question
Jan 18th, 2008

I have this host-flapping message. I already know what it is, and why I am getting it in this particular instance - a sick server cluster.

But does anyone know what the threshold is for the message to be generated, and whether the threshold can be configured?

Kevin Dorrell


I have this problem too.
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smothuku Thu, 01/24/2008 - 22:57

Hi kevin ,

last week end we were planning to put the nortel FW's into production.

We were getting the following message on 4507R switches after terminating nortel FW's on the switches.

1w0d: %C4K_EBM-4-HOSTFLAPPING: Host 00:00:5E:00:01:0F in vlan 15 is flapping between port Gi3/1 and port Po5ping 19

1w0d: %C4K_EBM-4-HOSTFLAPPING: Host 00:00:00:00:FE:21 in vlan 15 is flapping between port Po5 and port Gi3/1

setup is as follows.

nortelFW1(port5-sync)--(port5)nortel FW2 .

| |

4507R sw1 (HSRP & Etherchannel)4507Rsw2

Vlan 15 is defined on both switches.

Vlan 31 , 32 ,33,51 and 52 are deifned on nortel FW.

Valn 15 port is access port and remaining are trunk ports.

Both FW's are in sync i.e port 5 is connected back to back.

G1/1 and G2/1 of switches are connected back to back for etherchannel bundling.

I've noticed following

1. When ether-channel is up , we are getting the hostflapping messages and we are not able to ping to FW2 from any any of the Switches.Not even from FW1.

2.If i shut down the port-channel , then FW1 is able to reach from sw1 and fw2 from sw2.

We were not getting the messages.

Whenever port channel is coming into picture at that time we are facing this problem.

Any help would be appreciated.



royalblues Fri, 01/25/2008 - 01:29

Kevin, I dont think there is a command to configure the threshold


THe first mac-addresses you mention is a Multicast mac-address. can you check who is actually using this address

The other one not at all a valid mac-address. Microsoft uses some mac-addresses for NLB 0201AC100001



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