STP behavior

[MrMarco]

Hi,

I need some help figuring something out with STP.

My environment is still begin setup up, consists of the following

Core switch 1 - Root bridge priority 0

Core switch 2 - priority 4096

Stack A - 2 switches, switch connected to the core switch 1 primary

Stack B - 2 switches, switch connected to the core switch 1 primary

Stack C - 2 switches, switch connected to the core switch 1 primary

Single meraki switches

Everything is connected redundanty, so the single meraki switches have a connection directy to both core switches, designating the corrects for spanning-tree (Block to SW002, designate port to SW001 as active)

My stacks however, show unexpected behaviour.

For all the stacks the primary (active) switch is connected to SW001 and the secondary (member) switch connected to SW002. STP however decides to STP block the port on the active switch to SW001 and use the SW002 as shortest path to the root bridge (SW001). This behaviour is seen on 2 out of 3 stacks.

Anyone got any pointers on how to troubleshoot this behaviour, or correct the situation?

[PhilipDAth]

Networks with looks in them are often problematic.

Can the two core switches be stacked together?

[PhilipDAth]

Are all the links the same speed?  E,g. 10Gbe?

You could try increasing the priority of switch2 to something like 16384 (instead of 4096), but I doubt this is the issue.

[PhilipDAth]

Have you try power cycling the switch stacks that are using the wrong uplinks?

[PhilipDAth]

Is VLAN1 configured as the native VLAN on all trunks, and is VLAN1 allowed on all trunks?

Have you configured any other spanning tree features like root guard, loop guard, etc?

[MrMarco]

Hi Philip, to answer your questions:

* Forgot to put it in the image, but the Core switch 1 is configred as an L3 switch with VLAN gateways, the Core switch 2 is the warm spare for this. Switch 1 and Switch 2 are linked together with an aggregate trunk

* Link speeds are the same for the ports, and I cant give the stack members separate STP priorities

* Tried both port cycle (shut/no shut of port the Meraki way) and rebooting the switch stacks

* VLAN 1 is not the native VLAN on the trunks, but is allowed on all Trunks. All trunk ports are configured the same (Native VLAN 900, allowed VLAN 1-1000)

* Configured no other spanning-tree features besides giving priorities to the switches so the correct Root is elected.

[PhilipDAth]

Hmm.

Are they running a current stable version or firmware (or better)?

Can you cange the core switches so they are stacked?

[ww]

When you look at stack b switch2. Who does that switch report as root?

[MrMarco]

Hi WW,

Switch2 of stack B reports Switch1 as Root via the port connected to Switch2