Port 21 disabled→designated

[Melvin1]

FIRMWARE

Up to date

Current version: MS 14.33

Can you tell me what this means?

SERIAL NUMBER

Q2EW-DRSR-99XT

Jan 25 09:07:40 Port STP change

Port 21 disabled→designated

Jan 25 09:07:40 Port status change

port: 21, old: down, new: 1Gfdx

Jan 25 09:07:36 Port STP change

Port 21 designated→disabled

Jan 25 09:07:36 Port status change

port: 21, old: 1Gfdx, new: down

Jan 25 07:34:58 Port STP change

Port 4 disabled→designated

Jan 25 07:34:58 Port status change

port: 4, old: down, new: 1Gfdx

[KarstenI]

Port 4 got a link, Port 21 lost a link and got the link back.

[Melvin1]

Is the link dropping due to the device dropping the link or is it due to spanning-tree dropping the link? 

[KarstenI]

This is typically the device. 

[Melvin1]

The event type is STP - Spanning Tree. Do the NIC cards report back to the switch why it dropped? 

I want to isolate the issue because if it is a spanning tree loop, then I am crawling under a bunch of desks tracing cables.  

[ww]

If it was a stp loop, your network would probably be unusable. And i think the meraki switch mangement could go offline and no logging would be send to the dashboard

I think someone disconnected the port. Or maybe the device rebooted.

What kind of device is connected to that port?

[Melvin1]

Notice the lower case ports and the upper case Port. - strange 

It appears that the ports are failing and reconverging with a new root.

The complaint is the systems slow down to the point they are unusable.  

Jan 25 09:11:09 Port STP change Port 28 designated→root

Jan 25 09:11:09 Port STP change Port 28 root→designated

Jan 25 09:07:40 Port STP change Port 21 disabled→designated

Jan 25 09:07:40 Port status change port: 21, old: down, new: 1Gfdx

Jan 25 09:07:36 Port STP change Port 21 designated→disabled

[RaphaelL]

What is connected to port 28 ?

[KarstenI]

The NICs don't report anything back and they don't participate in STP. The logs show a completely normal behaviour. When a port comes up it has to transition to designated to make sure the attached device will receive traffic.

[Melvin1]

Port 28 is connected to 3750x.

Platform cisco WS-C3750X-48P
Device ID HS-E430-3750X.bpsd.edu
Port ID GigabitEthernet3/0/47

I am seeing port flapping on the 3750, which I had assumed the flapping was caused by devices connecting to different access points on the same switch.

[Melvin1]

I agree that the NICs don't participate in spanning-tree.   Every few seconds the switch is electing a new root. Which is what the switch is indicating.  

I guess I am going to crawl under some desk.  What would be nice is if I could disconnect the trunk port and view the Meraki switch logs. I would just like to isolate the issue before crawling under desk.

[Ryan_Miles]

You should never post your Meraki serials on Community (or any public site)

[Melvin1]

Thanks for letting me know. Are you a person or a bot?  I am trying to find where I posted a serial #.

[Ryan_Miles]

In your original post, 6th line.

[Melvin1]

Sorry, my apologies.   

Can you tell me what is generating the errors:

Jan 25 09:11:09 Port STP change Port 28 designated→root

Jan 25 09:11:09 Port STP change Port 28 root→designated

[Ryan_Miles · Accepted solution]

You have 9 Meraki switches in this network. More Meraki switches in another network name that appear to physically be in this same topology with a stack configured as the STP root. And more Catalyst switches, but I'm unsure how those are connected in this topology. It appears perhaps the Catalyst switches sit between two Meraki switch networks?

Switch port 28 from your log above reports as connected to a Catalyst 3750.

If you've not already done so you should run this by your Meraki TSA for design review. Perhaps there's a STP mode mismatch somewhere in the network path or non matching VLAN configs of ports connecting switches to other switches. Hard to say without a thorough review and access to all configs in this topology. 

[alemabrahao]

Did you configure the STP priority? It is a best practice to set the Core switch to the lowest priority and for access switches you can use the default priority.

Also, verify that there is no other cable connected to the 3750x that could be causing a network loop.

 I would recommend som Key points:

1. Use Rapid STP with command spanning-tree mode rapid  (default is STP )

2.  Determine the best switch to be Root switch and set Bridge Priority (spanning-tree vlan x priority 0)  

3. Adjust ports costs to Root switch (spanning -tree vlan x cost x) 

STP decisions are based on the following sequence of four conditions:
1. Lowest root bridge ID
2. Lowest root path cost to root bridge
3. Lowest sender bridge ID

4. Lowest sender port ID