Mac flapping from wireless contoller

[robertotron007]

Hi Guys,

I am trying to figure out why we have Mac flapping on our network. Core B is reporting that that two hosts are flapping between the port for our wireless controller Gi1/1 and the etherchannel for the Server Switch. Both hosts that it is reporting are Sun Servers with no wireless on them. I saw this happen with a users computer who was attached to a switch in the RPVST domain. We never figured out why it was happening and he just decided to use his wireless instead of the hard wire. But now this issue has surfaced again since there was a duplicate IP on the network which has been resolved.

The wireless controller port gi1/1 is an access port in vlan 100.

.Oct 22 10:27:44: %C4K_EBM-4-HOSTFLAPPING: Host 00:D0:68:xx:xx:xx in vlan 1 is flapping between port Gi1/1 and port Po1

.Oct 22 10:28:12: %C4K_EBM-4-HOSTFLAPPING: Host 00:21:28:xx:xx:xx in vlan 1 is flapping between port Po1 and port Gi1/1

.Oct 22 10:32:31: %C4K_EBM-4-HOSTFLAPPING: Host 00:21:28:xx:xx:xx in vlan 1 is flapping between port Gi1/1 and port Po1

.Oct 22 10:32:44: %C4K_EBM-4-HOSTFLAPPING: Host 00:D0:68:xx:xx:xx in vlan 1 is flapping between port Gi1/1 and port Po1

.Oct 22 10:33:09: %C4K_EBM-4-HOSTFLAPPING: Host 00:21:28:xx:xx:xx in vlan 1 is flapping between port Po1 and port Gi1/1

.Oct 22 10:34:20: %C4K_EBM-4-HOSTFLAPPING: Host 00:21:28:xx:xx:xx in vlan 1 is flapping between port Gi1/1 and port Po1

.Oct 22 10:35:58: %C4K_EBM-4-HOSTFLAPPING: Host 00:21:28:xx:xx:xx in vlan 1 is flapping between port Gi1/1 and port Po1

.Oct 22 10:37:03: %C4K_EBM-4-HOSTFLAPPING: Host 00:21:28:xx:xx:xx in vlan 1 is flapping between port Gi1/1 and port Po1

.Oct 22 10:38:08: %C4K_EBM-4-HOSTFLAPPING: Host 00:21:28:xx:xx:xx in vlan 1 is flapping between port Po1 and port Gi1/1

.Oct 22 10:41:50: %C4K_EBM-4-HOSTFLAPPING: Host 00:21:28:xx:xx:xx in vlan 1 is flapping between port Gi1/1 and port Po1

.Oct 22 10:43:12: %C4K_EBM-4-HOSTFLAPPING: Host 00:21:28:xx:xx:xx in vlan 1 is flapping between port Gi1/1 and port Po1

ServerSwitch

interface Port-channel1

switchport mode trunk

end

interface GigabitEthernet0/21

description E-channel 1

switchport mode trunk

channel-group 1 mode on

!

interface GigabitEthernet0/22

description E-channel 1

switchport mode trunk

channel-group 1 mode on

!

interface GigabitEthernet0/23

description E-channel 1

switchport mode trunk

channel-group 1 mode on

!

interface GigabitEthernet0/24

description E-channel 1

switchport mode trunk

channel-group 1 mode on

!

!

!

!

Name: Po1

Switchport: Enabled

Administrative Mode: trunk

Operational Mode: trunk

Administrative Trunking Encapsulation: dot1q

Operational Trunking Encapsulation: dot1q

Negotiation of Trunking: On

Access Mode VLAN: 1 (default)

Trunking Native Mode VLAN: 1 (default)

Administrative Native VLAN tagging: enabled

Voice VLAN: none

Administrative private-vlan host-association: none

Administrative private-vlan mapping: none

Administrative private-vlan trunk native VLAN: none

Administrative private-vlan trunk Native VLAN tagging: enabled

Administrative private-vlan trunk encapsulation: dot1q

Administrative private-vlan trunk normal VLANs: none

Administrative private-vlan trunk private VLANs: none

Operational private-vlan: none

Trunking VLANs Enabled: ALL

Pruning VLANs Enabled: 2-1001

Protected: false

Unknown unicast blocked: disabled

Unknown multicast blocked: disabled

Appliance trust: none

____________________________________________________

Core B Switch

interface Port-channel6

description ServerSwitch

switchport

switchport mode dynamic desirable

load-interval 30

!

interface GigabitEthernet2/1

description ServerSwitch

switchport mode dynamic desirable

media-type rj45

channel-group 6 mode on

!

interface GigabitEthernet2/2

description ServerSwitch

switchport mode dynamic desirable

media-type rj45

channel-group 6 mode on

!

interface GigabitEthernet2/3

description ServerSwitch

switchport mode dynamic desirable

media-type rj45

channel-group 6 mode on

!

interface GigabitEthernet2/4

description ServerSwitch

switchport mode dynamic desirable

media-type rj45

channel-group 6 mode on

!

!

!

!

Name: Po1

Switchport: Enabled

Administrative Mode: dynamic desirable

Operational Mode: trunk

Administrative Trunking Encapsulation: negotiate

Operational Trunking Encapsulation: dot1q

Negotiation of Trunking: On

Access Mode VLAN: 1 (default)

Trunking Native Mode VLAN: 1 (default)

Administrative Native VLAN tagging: enabled

Voice VLAN: none

Administrative private-vlan host-association: none

Administrative private-vlan mapping: none

Administrative private-vlan trunk native VLAN: none

Administrative private-vlan trunk Native VLAN tagging: enabled

Administrative private-vlan trunk encapsulation: dot1q

Administrative private-vlan trunk normal VLANs: none

Administrative private-vlan trunk associations: none

Administrative private-vlan trunk mappings: none

Operational private-vlan: none

Trunking VLANs Enabled: ALL

Pruning VLANs Enabled: 2-1001

Unknown unicast blocked: disabled

Unknown multicast blocked: disabled

Appliance trust: none

[Arumugam Muthaiah]

Hi Steve,

The %C4K_EBM-4-HOSTFLAPPING:Host [mac-addr] in vlan [dec] is flapping between port [char] and port [char] error message signifies that the specified host (Host 00:21:28:xx:xx:xx) is detected as a source address on multiple ports. Typically, a host is supposed to be learned on only one port.

You need to trace that mac down to the end device and see why this packet taking both pathes to your switch.

Example:

In case if the the host is connected to ports x/y, and x/y runs a type of clustering or redundancy and has an issue with this mechanism. If the MAC address specified in the error message can be traced, this is likely the issue. For an example, refer to this error message:

%C4K_EBM-4-HOSTFLAPPING: Host 00:21:28:xx:xx:xx in vlan x is flapping between port Gi x/y and port Gi x/y

• The MAC address 00:21:28:xx:xx:xx appears to be associated to Microsoft's Network Load Balancing (NLB) Service Heartbeat. It is suggested that the connected device (Microsoft host) be checked for causing these messages.
  

• If the MAC address in the error message is related to Microsoft Network Load Balancing (NLB), then you need to disable or clear the Network Load Balancing check box.
  

• To display spanning-tree state information for the VLAN ID mentioned in the error message, issue the show spanning-tree vlan vlan_id detail command and look for the last topology change
  

Regards,

Aru

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[robertotron007]

Thanks for your response.

I forgot to mention above that this is being sourced from a Sun server so I doubt it is using Microsoft Load Balancing.

Also, I have portfast enabled on all access ports so spanning-tree topology does not change very often. As you can see from the exact, the port if flapping every few minutes.

Any other ideas?