How To make priority to Link

[vikas kumar]

Dear all

we have multiple switch in our network. Switch 1 is spanning tree root switch for all VLANs.

we are running 10 VLANs is our network

i have configured two links to each switch. primary link is fiber connected to switch 3 and switch 4 via switch 2

Backup is directly from switch 1 to switch 3 and switch 4.

when i am enabling Both link traffic is flowing from backup link.

how can i give priority to primary link, if primary link fails traffic flow on backup link

please help

vikas

[mvsheik123]

Hi Vikas,

Try spanning-tree cost under the backup interface. Cofigure cost higher than the primary link cost. It mgith fix the issue.

hth

MS

[Jan Hrnko]

Hi Vikas,

You could do this by configuring cost of the link but I think that even better way is to configure STP port priorities. Default priority of the port is 128, you can increase or it (higher is worse) or decrease it (lower number is better priority) in the increments of 16.

Priority: 0 is best - 240 is worst.

So you should decrement the priority number of port on Switch1 towards switch2 (decrementing it makes it better).

If you use default priorities on all ports of other switches you can for example use priority of 112.

Example - Improving priority on port fa0/1 for VLANs in range 1-10 on Switch1:

Switch1(config)#interface fa0/1
Switch1(config-if)#spanning-tree vlan 1-10 port-priority 112

In this example, I assume that port fa0/1 is the port of Switch1 on link between Switch 1 - Switch2.

Or you can increase priority number (thus making the priority worse) towards the other two ports of switch3 and switch4.

Best regards,

Jan

----------------------------------------

Correction: I have corrected previous errors.

Message was edited by: Jan Hrnko

[vikas kumar]

Hi jan

thanks for reply,

I have incresed priority 240 Switch 3 and 4 ports connected to switch1.

but still traffic going via Radio ( direct) link.

please assist.

best regards

vikas

[Dan-Ciprian Cicioiu]

Hi Vikas,

There are 2 solutions :

  - port-priority - you should configure it on the root bridge - lower better - multiple of 16

               on Sw1 toward SW2

                         spanning-tree vlan 10 port-priority 16

   - cost - you can configure on the other switches - lower better

               On Sw2 toward Sw1

                         spanning-tree vlan 10 cost 1

Regards

Dan

[vikas kumar]

Dear dan

thanks for reply

i have tested both options but still traffic is going VIA radio link.

even I increased priority  (240 ) to port on switch1 toward to switch3, and priority  (32) to switch 1 port toward to switch 2.

cost on both switch are

Switch2 toward switch 1 -- cost 4

Switch3 toward switch 1 -- cost 19

i have not changed any cost peramitter becouse already lower on switch 2

but still same result.

please assist

Regards

vikas kumar

[Dan-Ciprian Cicioiu]

Hi Vikas,

Could you tell me where in your drawing is the radio link ?

If you do not want to use the "Backup links" at all, only in the case of Primary link failure you will have to configure also Switch 3 and Switch 4 , lowering th cost toward switch 2 . This way the path from Switch 3 and 4 to swtch 1 will be lower through Switch 2 .

Switch 3 and 4 toward Switch 2

spanning-tree cost 1

In order to work , the aggregated cost between (SW1 and SW2) + (SW3 and Sw2) should be lower then the cost between (SW3 and SW1) which in your case is 19. The same for SW4

Regards

Dan

[vikas kumar]

Dear DAN

thanks for reply,

after changing cost toward to switch it is working fine.

thanks so much for help and support.

regards

Vikas kumar

[Dan-Ciprian Cicioiu]

Hi Vikas ,

I am glad to hear that 

If your issue was solve set the thread as answered

Regards

Dan

[Jan Hrnko]

Hi Vikas,

I am sorry but I have incorrectly identified your problem. Sorry again for my misunderstooding. You could bring back priority of 128 to that ports.

This means that you can resolve the problem with cost parameter on Switch2 or in the opposite way - as Dan suggests (on switch1). But I have assumed that you have same cost of links (primary and backup) and if you haven't then you need to resolve the problem using cost parameter. It is beacuse of the fact that the port-priority is only used in election process if the cost are the same.

Sorry again for the inconvenience.

Best regards,

Jan.

[vikas kumar]

Dear Jan

no issue my friend, as i replied to dan

switch2 toward switch 1  spanning-tree cost is lower than switch 3

it should work but  still traffic going via radio link when both links are enable.

Regards

vikas