Link Flapping

[ney25]

Hi NetPro,

recently, i noticed lot of link flapping in my Cat 4509 switch. the error messge shown as " %SYS-4-P2_WARN: 1/Host 00:0e:35:90:50:25 is flapping between port 1/1 and port 6/1 " , any idea how to prevent this happened again ?

Thanks alot,

Regards,

Jack

[lgijssel]

The most likely cause is spanning-tree instability.

Appearently the indicated host has two paths to the rest of the network, and there is a regular switchover between both paths. Bad links or extremly heavily loaded ones can cause this as they may cause a loss of BPDU's.

Regards,

Leo

[ney25]

Hi Leo,

firstly, really thanks for your reply. well i understand the spanning-tree will cause the flapping . but, now this device is using for Wireless Access Point 1200 Series. in the AP i have 2 Vlans in the device. and the port configuration i am using Trunk instead of spanning-tree. but, the flapping still occur. any idea how to troubleshoot with this ?

Thanks alot,

Regards,

Jack

[lgijssel]

When you use Cisco, you will probably apply PVST (Per Vlan Spanning Tree). A Trunk is simply a link that carries multiple vlans. So one cannot say he uses trunk instead of spantree, you are using both!

When it is a wireless device you might have a situation where the device is constantly roaming between two access points. Increasing one AP's field strength or altering the channel allocations might be a good starting point.

Remember that two bordering AP's should each use one of the non overlapping channels: 1 6 or 11.

Regards,

Leo

[ney25]

Hi Leo ,

yes, u are right . i am using PVST. and in the Access Point i am applying 2 Vlans (Which is Vlan 1, Vlan 10). that's why i am using Trunk. so, in this case single access point only. but, they still caused the Flapping.

so, my problem is fapping always caused from port to port .

Regards,

Jack