Hey @Johan Basic things first. Remember the MX is not a switch and does not speak STP and does not support UDLD either. So what you are dealing with is one switch only which is your root bridge too. Both ends of a link need to support UDLD for this feature to initiate. Since the MX does not support it, enabling UDLD in your topology is useless Loop guard does not apply to your topology either. I'd not apply it. For your topology enabling RSTP without any STP guard options (root, loop, bpdu-obviously) is enough. doing to should give you one of your fibre links in forwarding and the other in blocking. A note on UDLD, as mentioned in your case is useless since the MX does not support it, in valid cases when UDLD is enabled, Meraki recommends to do it in "Alert Only" mode https://documentation.meraki.com/Architectures_and_Best_Practices/Cisco_Meraki_Best_Practice_Design/Best_Practice_Design_-_MS_Switching/General_MS_Best_Practices Finally, regarding the "correct" topology. I am afraid that what you have is correct because of your two uplinks to the same box (MX). if you disable one of the uplinks you should see a more comprehensible topology. with both enabled you should be able to see a check box "Show redundant links" which makes the topology a tiny bit more comprehensible.
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