vlan 1 is flapping between port

[mgerguis]

Would appreciate help to resolve the above mentioned error as its disturbing network operation, my guess it is due to spanning tree problem though I reviewed it several times but still one switch is showing as root when it should not & tried to change but not sure what is best way to do so

{

SW4-C2960S-24P#sh spanning-tree

‌

MST0

‌

Spanning tree enabled protocol mstp

‌

Root ID Priority 32768

​‌

Address 2834.a25f.b100

​‌

This bridge is the root

​‌

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

‌

Bridge ID Priority 32768 (priority 32768 sys-id-ext 0)

​‌

Address 2834.a25f.b100

​‌

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

}

the other ports affected are connected to Wi-Fi access points & one to the uplink,

causing all Wi-Fi users to be disconnecting due to the flapping.

it is occurring on multiple switches & just started several weeks ago before all was working ok for several years,

only change was recently replaced one switch which broke down.

[Georg Pauwen]

Hello,

adding new switches can be tricky, especially if you have not (or have forgotten to) reset the revision number.

Either way, I don't know what your topology looks like, but on the switch you do want to be the root switch, configure:

spanning-tree mst 0 priority 1

[mgerguis]

Thanks for your answer

The topology is :

Core switch <-uplink-> Data Switch(C2960x-48) <-uplink-> POE Switch (C2960s-24) <-Uplink-> (C1832i)

my worry is why the C2960s is getting through STP to be the root, also flapping between the C1832 uplink & C2960x

please re-check & if safe will follow with above mention settings

[paul driver]

Hello
TBH I wouldn’t suggest you make any changes until you understand the consequences of
changing stp in production network, you could make things actually worse than it is now.

Can you confirm if you are just running MST throughout your lan estate or just on that replacement switch?

Do you have a mixture of switches or is it all cisco

[mgerguis]

Thanks for your reply

Yes, you are correct the further I try some times it is getting worse.

Yes it was the 1st thing to look up & check that all switches on LAN are on MST, this was rectified as some were not.

No it is a mixture, but the funny thing is only flapping is showing on Cisco connections not sure why?

[Georg Pauwen]

Hello,

I agree with @paul driver , seeing a topology diagram of your setup showing how everything is connected would be helpful. Do you have that, and can you post it ?

The C1832i that means an Aironet ?

[mgerguis]

Hi again,

please find the network topology attached

Correct the C1832i is "AIR-AP1832I-E-K9" / Aironet.

Thanks in advance for any advise.

regards,

[Georg Pauwen]

Hello,

which of these switches is the SW4-C2960S-24P (the root) ?

[mgerguis]

Hi,

please see the attachment, highlighted it.

thanks,

[paul driver]

Hello

---

@mgerguis wrote:

all switches on LAN are on MST, this was rectified as some were not.

No it is a mixture, but the funny thing is only flapping is showing on Cisco connections not sure why?

---

So you need to make sure that ALL switches are running the same MST configuration and revision number, secondarily suggest not to manually prune vlans on any trunks as MST is ran on a per instance stp and not per-vlan, otherwise you could have a protential to cause black holing of traffic, or loops.

Depending on how large your lan estate is, Also check your switches and see if any have trunks have established that shouldn’t have or bpdufiltering applied causing a loop.

[mgerguis]

Hi,

would appreciate if you could guide on how to check MST version as I am not sure on this part.

no manual VLan prune is done, but I fear the MST / STP is some how causing this loop / black hole

our current Lan layout spread around 12 Switches/12 Access Points,

Checked for current Trunks in place all looks are set "Dynamic desirable"

would appreciate if you kindly explain regarding the bpdu filtering, though nothing set from my side still would like to re-check in-case something is missed.

thanks in-advance, appreciate the help

[paul driver]

Hello

Having dynamic trunking is simple to apply but can cause an issue as you leave yourself open to trunks being formed when you don’t wish for to be- hence manually forcing your trunks ports to be in an administrative trunk mode I would say is preferred and any edge ports tobe forced to in a administrative mode of access with stp portfast and bupduguard applied 

cisco example:

trunk port

int x/x

switchport

switchport mode trunk 

access-port

int x/x

switchport mode access

spanning-tree portfast

spanning-tree bdpuguard enable

To check you mst configuration 

show spanning-tree mst configuration 

To check for bpdufilter

sh run | in bpdufilter