HOST in Vlan Flapping

Unanswered Question
Apr 29th, 2009

Hello freinds,

Getting some messages from 4500 series L3 swithc about Vlan flapping.

SEQ HOST FACILITY DATE TIME PROGRAM MESSAGE

41542 10.100.9.10 local7 12:13:15 Syslog %C4K_EBM-4-HOSTFLAPPING: Host 00:15:C6:0D:08:FF in vlan 111 is flapping between port Gi1/1 and port Gi3/4

41541 10.100.9.10 local7 12:12:59 Syslog %C4K_EBM-4-HOSTFLAPPING: Host 00:15:C6:0D:08:FF in vlan 111 is flapping between port Gi1/1 and port Gi3/4

41540 10.100.9.10 local7 12:12:16 Syslog %C4K_EBM-4-HOSTFLAPPING: Host 00:15:C6:0D:08:FF in vlan 111 is flapping between port Gi1/1 and port Gi3/4

41539 10.100.9.10 local7 12:12:06 Syslog %C4K_EBM-4-HOSTFLAPPING: Host 00:15:C6:0D:08:FF in vlan 111 is flapping between port Gi1/1 and port Gi3/4

41538 10.100.9.10 local7 12:11:44 Syslog %C4K_EBM-4-HOSTFLAPPING: Host 00:15:C6:0D:08:FF in vlan 111 is flapping between port Gi1/1 and port Gi3/4

41537 10.100.9.10 local7 12:11:17 Syslog %C4K_EBM-4-HOSTFLAPPING: Host 00:15:C6:0D:08:FF in vlan 111 is flapping between port Gi1/1 and port Gi3/4

Please suggest.

Regards

Regards

I have this problem too.
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crow930us Wed, 04/29/2009 - 23:46

You might have a spanning tree loop. Host 00:15:C6:0D:08:FF in vlan 111 is detected as a source address on ports Gi1/1 and port Gi3/4. Typically a host is supposed to be learned on only one port. All traffic from the specified

host is temporarily dropped. After 15 seconds, forwarding is reenabled.

If spanning tree is disabled make sure there are no spanning tree loop in your network.

cisco.net Wed, 04/29/2009 - 23:49

Hii,

While tracing the mentioned MAC address we finding the the same belongs to Vlan 111 logical interface.

Cisco_Sw1#sh int vlan 111

Vlan111 is up, line protocol is up

Hardware is Ethernet SVI, address is 0015.c60d.08ff (bia 0015.c60d.08ff)

Regards

Giuseppe Larosa Thu, 04/30/2009 - 00:36

Hello Jimmy,

there is a loop and the switch is complaining of seeing its own packets received back on your ports.

For example these could be HSRP hello messages sent with a source MAC = SVI MAC address.

verify what is connected on those two ports.

I would also try to shut down one of them.

Hope to help

Giuseppe

cisco.net Thu, 04/30/2009 - 01:38

Hello Giuseppe,

Gig1/1 of the switch is UPLINK/Trunk port (connected to core/agg cisco L3 switch) and Gi3/4 is the access port with Vlan 111 from where one ethernet connectivity is extended.

As for as HSRP is concerned ..the same is not running anywhere on the switches.

regards

cisco.net Sat, 05/02/2009 - 22:37

Dear All,

Can anyone have some suggestions for finding out the problem.

regards

smothuku Mon, 05/04/2009 - 22:59

Hi ,

Make sure that both the switches are transperant as per vtp mode...

do clear arp on both the swiches and check the logs...

Clear mac-address table also...if you do this both the swithces forms mac table freshly and most of the time problem of host falpping is been resolved by clear mac-addresses.

Hope it resolves your issue.

Thanks,

Satish

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