Need confirmation that I'm not about to create a switch loop

[michio]

I am about to establish a new critical link from our top of rack Mellanox switches to the rest of our network via a Cisco 9300 stack. It will replace the older slower critical link. spanning tree is not enabled with the Mellanox switches and i will not be able to turn it on. what I want to confirm before I pull the trigger is this. How to I make absolutely sure that I don't accidentally create a loop. my current set up is that I have made a normal connection on the Mellanox and on the 9300 side I have a "switchport trunk allowed vlan none". I am planning on cutting over the vlans one at a time. Is that enough or is it possible for frames to slip through on vlan 1 or some other thing that I am not considering? should i disallow traffic on both sides? 99% sure I am good here but it's a bit terrifying to think i might blow up a big network with a loop accidentally. Thanks for any advice.

[MHM Cisco World]

cannot disable stp in mellabox or in cisco sw?

[Reza Sharifi]

How is everything is connected together right now, and how are you planning on connecting everything to the new 9300? Can you post a simple diagram of the before and after migration? In general, if switches are only single attached and you are not looping them back together, there is no risk of stp, but a diagram can be very helpful.

HTH

[MHM Cisco World]

for Me I dont like suggest any thing regarding the STP since any small detail can make Network drop due to L2 LOOP.
but here I would like to suggest to check some feature 
Mellanox not config STP meaning there is no BPDU send, How I protect c9300 from 

IF BY MISTACK mellanox run STP and send BPDU, we need to config the C9300 with BPDU guard to make C9300 detect the BPDU and immediately err-disable the port (no auto recovery).

this make both C9300 and mellanox port in FWD status and if Mellanox send BPDU the port is err-disable.
again friend please be careful.
good luck

[Leo Laohoo]

Provide the network diagram to make things clear.

[Jon Marshall]

It's not really a question of accidentally creating a loop, if you have two separate connections from the Mellanox switch to the same switched network then you have created a loop. 

Normally STP would step in and block one of the links but if you are not running STP then yes you need to be very careful how you migrate the vlans across between the links. 

If you are planning on switching the vlans across one at a time then there will be a potential blip in traffic for each vlan as you would have to remove from the existing link before adding to the new link so why not have an outage window and move all vlans at once ? 

It could well be that you have no issues at all but in my experience L2 can be more unpredictable than L3 and I would always look to do this work in a planned maintenance window.

Jon