Triangle Link - Spanning Tree

[Boon Keat Gan]

Hi All,

We tried to create a redudancy link between 3 building. When we connect the 3rd link (Red Line) and keep receiving the following error message.

*Nov  3 19:27:44.932: %SW_MATM-4-MACFLAP_NOTIF: Host 6c41.6a13.3580 in vlan 17 is flapping between port Gi4/0/44 and port Gi1/1/1
*Nov  3 19:27:44.957: %SW_MATM-4-MACFLAP_NOTIF: Host 001e.0b66.8561 in vlan 19 is flapping between port Gi4/0/44 and port Gi1/1/1
*Nov  3 19:27:44.965: %SW_MATM-4-MACFLAP_NOTIF: Host 88ae.1dad.2fd3 in vlan 19 is flapping between port Gi1/0/4 and port Gi1/1/1
*Nov  3 19:27:45.032: %SW_MATM-4-MACFLAP_NOTIF: Host 0013.2304.49f6 in vlan 25 is flapping between port Gi1/1/1 and port Gi4/0/44
*Nov  3 19:27:45.074: %SW_MATM-4-MACFLAP_NOTIF: Host 0013.2304.4a1b in vlan 25 is flapping between port Gi1/1/1 and port Gi4/0/44
*Nov  3 19:27:45.091: %SW_MATM-4-MACFLAP_NOTIF: Host a01d.48b7.dcdb in vlan 19 is flapping between port Gi4/0/44 and port Gi3/0/28
*Nov  3 19:27:45.166: %SW_MATM-4-MACFLAP_NOTIF: Host 0050.569e.6d67 in vlan 2 is flapping between port Gi4/0/44 and port Gi1/1/1
*Nov  3 19:27:45.234: %SW_MATM-4-MACFLAP_NOTIF: Host 0013.2307.764a in vlan 25 is flapping between port Gi1/1/1 and port Gi4/0/44
*Nov  3 19:27:45.275: %SW_MATM-4-MACFLAP_NOTIF: Host 28d2.4476.172f in vlan 17 is flapping between port Gi4/0/44 and port Gi1/1/1

I cannot figure out what is wrong with the setting. Any advise?

[Boon Keat Gan]

Correction to above diagram

SW85 Connection to SW81 should be using port Gi 1/1/1

[shuja_abbas]

Try usng MSTP  .. and on the trunk ports use spanning tree point to point 

[Boon Keat Gan]

Do you mean this link? http://blog.ine.com/2010/02/22/understanding-mstp/

But if my configuration have 2 same vlan how should i go about it?

[Rajeev Sharma]

Hey,

I suggest locating the original location of any of these machines from SW85 and then start looking the STP port states in other direction.

Say originally users are reachable over link G3/1/1 so ideally as per STP link G4/0/44 needs to be blocking for these user/vlans. Keep tracing the spanning tree port states over the other link and i am sure you will find something useful.

HTH.

Regards,
RS.

[Boon Keat Gan]

The error keep prompting non stop and it is almost impossible to check on the switch.

[Rajeev Sharma]

Try checking on switches other than SW85.

HTH.

Regards,

RS.