Ring connection between 3 Cisco switches

[Mahmoud Marie]

Hello 

I have 1 Cisco 9200 switch connected to 2 other Cisco switches with Fiber connection, as the below diagram:

What the configuration for STP should I apply if need to connect Site B with Site C.

Appreciate your help 

Thanks

[Jon Marshall]

Depends on the number of vlans etc. 

If you have everything in the same vlan then you need to pick a path you want to use because you have a L2 loop in the diagram so you cannot go direct between each site ie. the traffic between 2 of your sites will have to go via the other site as one of the links will be blocking. 

Jon 

[Georg Pauwen]

Hello,

as John said one of the links will be blocked by STP. I would look at the traffic patterns, if e.g. the traffic between Site A and Site B is more than with Site C, I would configure the direct link to Site C as the one blocked by STP.

[Giuseppe Larosa]

Hello @Mahmoud Marie ,

STP will block one link to prevent bridging loops.

The best choice is to make the wireless link between Site B and Site C a backup path used only when needed

It should be enough to place site A as root bridge for all VLANs

You can use spanning-tree vlan X cost 100 when you want to make a link a backup path for VLAN X

the command spanning-tree cost 100 will apply to all VLANs  / STP instances if you are using PVST or Rapid PVST.

I suggest this because a RF link cannot be as reliable as a wired fiber based link.

Hope to help

Giuseppe

[paul driver]

Hello
Based on your topology the most probable higher stp interface costs by default would be on the physical links over lower stp cost of the wifi links, So if you make site A the stp root for all vlans then both sited B-C direct connection to site A should by default become root ports and the wifi interconnection between site B-C would become an stp backup with one side blocking- That said its better to be deterministic in your stp topology design and manually stating the stp costingto the root can be a sure way of doing this.