Stack member reload causes small outage

[RaphaelL]

Hi ,

We have a simple topology.   Access layer is L2 Meraki Stacks with MS350s running 14.5. Distribution Layer is Cisco Catalyst C6800 series.

We had an issue with a specific stack of 7 MS350. We had to reload the last switch from that stack. While the switch was reloading , the vlans flapped on the Cisco VSS. I was expecting to the interfaces leading to the stack to flap, which would have lead to the vlans flapping. ( a vlan can't be up/up if no configured interfaces are up/up ).

Here is the switch stack in question : 

The logs from the dashboard : 

And lastly the logs from the Cisco VSS :

You can see that Po108 never flapped :

My questions : 

1- What in the world happened ?

2- Why would the switch -7 ( the one that reloaded ) became root and everyone from that stack saw it as Root ? ( the Root bridge has a priority of 4096 , and the Meraki network is configured with 32768 )

3- Is it ''normal'' ? Can we protect our self from that ?

I will try to reproduce the exact same issue. I will reboot the exact same switch and I will monitor the behavior.

Thanks , 

[cmr]

@RaphaelL for starters you need to upgrade the switch firmware, 14.5 is about 26 versions out of date in the 14.x release train as 14.33.1 is the current stable release.

Secondly, in the stack which switch has the lowest MAC address, that will normally be the switch master.  Support can also determine which one is at any given time.  We had an issue where it was moving around a stack of MS355s in 14.27 (I think) that was then fixed.  If the lowest MAC is switch 7 then that is the master and rebooting it will cause a blip.

[RaphaelL]

Hi , Yes I'm aware about the firmware version. We've had so many issues with latests version . 14.5 was the most stable, we are slowly rolling out to 14.33. 

Here are the MACs ( 1 is top and -7 is bottom ) :

[cmr]

Switch 5 should be stack master then.  Was 7 a later addition as it has a totally different MAC?

[RaphaelL]

It might have been added to the stack. But this switch has been stacked for more than 2 years.