Cisco 3850 VLAN Flapping

[elsayedm1]

Greetings All,

i need your support urgently

i am working on security systems (CCTV & Others security system) the cameras connected to the core switches(3850) through Industrial Switches (COMNET) , once we connected the Industrial Switches to core switches flapping startes and we cannot ping any another devices

could you support me to solve this issue

[Flavio Miranda]

Hi

 Please, share the config from the core switch and the Industrial Switches. And please share a simple topology showing how are you connection everything

[balaji.bandi]

This looks for me spanning tree issue high level, but worh post the logs from Cat 3850., what version of code running on Cat 3850

is this connected port confiured as Trunk or access port ? post that interface config will be helpfull.

[elsayedm1]

thanks a lot for your responses 

please find the attached files and design 

[Jitendra Kumar]

It will be better to share specific port config with both switch side core and industrial.

Suspecting a spanning-tree issue and negotiation issue as well DTP enabled on the switch?

[Elliot Dierksen]

I agree with @balaji.bandi that this looks like a spanning tree problem. Are the industrial switches managed or unmanaged? Are there multiple links to the industrial switches and the upstream managed switches? If the answer to that last question is yes, that is your problem.

[elsayedm1]

Hello Elliot, 

about the ISW is : Managed Switches

Are there multiple links to the industrial switches : Only one line coming from the primary core switches and then ISW connected to second ISW, then second ISW connected back to secondary core switch. find the attached. 

[elsayedm1]

Thank you Elliot & Jitendra

Please find the attached , right now i know that the issue is STP

could you tell me what is the command i should add it on the both core switch to solve the issue?

your support is highly appreciated 

[Jitendra Kumar]

unable to understand if you have redundant connectivity then why STP is disabled diagram clearly saying  ISW 2 are in the loop.

you can better understand STP and config as well from the below URL

https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/5234-5.html 

[balaji.bandi]

because you using VLAN 1 as a default all over, you only have limited options here. (not sure you looking to extend VAN 10 ?)

make one of as bridge priority, so that will be root. and make config changes on other port root guard protection.

[Elliot Dierksen]

You have a loop at ISW 2 and the comment on your interfaces of the ISW's says 'no spanning tree'. Would you please elaborate on why you have that in place? You are forcing a loop. There would not be a loop if all the switches were executing spanning tree. ISW 2 would block either the link to ISW 1 or ISW 3 depending on which link was considered the root.