Switch is causing network outage

We have two Meraki MS320's as our core and 6 tertiary switches that are meshed to the core switches (two trunk cables - one cable goes to each core switch). The tertiary switches are SGE2010's and SG500X's.

Network mesh
One of the tertiary switches (SGE2010) can only have a single cable plugged into the core. If I plug in the redundant trunk cable, the entire network goes down. It seems that the Cisco switch thinks it is the root bridge and therefore has no Root or Alternate STP port. The Bridge ID and Root Bridge ID are the same. The ports are all either disabled or forwarding. The trunk ports are configured just like the rest of the tertiary switches. What I find odd is that the core switch has a lower MAC address number than the Cisco switch. If two switches fight for Root Bridge, doesn't the lower number win? ... and why isn't my Cisco SGE2010 accepting Root Bridge declaration from the Meraki?

A reboot of the switch didn't fix the problem.

You can refer to this question that led to the issue. It didn't appear to take place before the STP changes. (or may be it did happen but root guard is making it become more evident)

Thank you for any help.

Paul WagnerFriend To Robots and RocksAsked:
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Don JohnstonInstructorCommented:
What I find odd is that the core switch has a lower MAC address number than the Cisco switch.
That assumes the switches are running the same STP.  It looks like the Meraki switch support a couple of different versions of STP just like the Cisco.  But if they aren't running the same version then they won't see each other and strange things can happen.

But since you've got other Cisco switches of the same model, just look at one of the switches that is behaving and see what version of STP it's running then configure this misbehaving switch to run the same version.
Paul WagnerFriend To Robots and RocksAuthor Commented:
They are all running RSTP, and by all, I mean core and tertiary.
Don JohnstonInstructorCommented:
If you have two switches that are connected and they both think they're the root then either A) they're not communicating at all or B) they are not speaking the same language (in this case, spanning-tree).

Now as far as option A, it could be a unidirectional link.

That said, when only one of the uplinks is connected from the offending switch, does everything work fine?  If so, then there's no unidirectional link.

And if everything is working fine with the single uplink in place, what does the STP information show?  Does the SGE2010 recognize the Meraki as the root?
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Paul WagnerFriend To Robots and RocksAuthor Commented:
Yes, the tertiary switch works fine when only one cable is plugged in. I verified that it isn't the port by plugging only one cable in to both trunk ports. The problem only happens with both cables plugged in.

No, the SGE2010 still thinks it is the Root Bridge even though it is connected to the Meraki.
Don JohnstonInstructorCommented:
Okay, so you have a single uplink connected, traffic flows fine but both switches think they are the root.

Either they are not running the same spanning tree protocol or spanning tree is disabled on the port connecting to the other switch (this could be on the Meraki or the Cisco).
Paul WagnerFriend To Robots and RocksAuthor Commented:
I've tried different ports on the Cisco and different ports on the Meraki. RSTP is running on all of them.
Don JohnstonInstructorCommented:
When this switch is connected to the Meraki switch, what is the port state? I'm guessing Designated.

Can you connect this switch to one of the other Cisco's?
I know that the small business line of switches can have a different type of CLI, but would it be possible to post the scrubbed config of the offending tertiary switch? I have found that sometimes with the small business line looking at both gui and cli work best to troubleshoot because the gui doesn't always show all the config or it can be difficult to find the correct area to look.
Craig BeckCommented:
The fact that the whole network dies tells me STP isn't configured correctly.

Have you configured bpdufilter on the switch that causes an issue?
Paul WagnerFriend To Robots and RocksAuthor Commented:
The connected port is Designated
I will try connecting it to another Cisco tonight since I don't want to do it during working hours.

Config attached

BPDU guard is enabled for the access ports but not the trunk/uplink ports.

Here are some screenshots:
1- Port 24 of the "bad" Cisco is naming its own port 24 as the designated port ID... that's the port connected to the Meraki which should be telling it that the Meraki is the root bridge. This port's settings are identical to those of the other Cisco trunk ports with the exception of the bad one being Designated and the proper ones being Root/Alternate.

Port24 of offending switch
2- Here is the "bad" STP property screenshot

Bad STP properties
3- Here is a working switch with STP properties

Working switch STP properties
Paul WagnerFriend To Robots and RocksAuthor Commented:

I found that, for some reason a trunk port was missing a VLAN tagging. The VLAN tag that was missing happened to be the PVID of the port. This most definitely would cause the port not to communicate via STP with the Meraki.

How in the world did the port lose that VLAN tagging? I haven't a clue.

As soon as I assigned that VLAN tagging to the port, the "bad" switch picked up the proper Root Bridge and it is now part of the spanning tree for the rest of the network.

Now, I haven't actually plugged in the other cable from port 48 yet. I'll wait to do that tonight in case there is still a problem. Thanks for the great questions thus far everyone.

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Great to hear, look forward to the update!
Paul WagnerFriend To Robots and RocksAuthor Commented:
I stumbled upon the solution myself but the suggestions you had here helped me narrow down the possibilities.
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