To clarify also. I used to only have a single connection from MX to CORE 1. Since the MX doesn't support port-channeling etc.  Wanted to keep things simple.   Had it like that for almost 2 years, until CORE 1 at a site had an issue, which ended up taking down the guest network which the MX was the gateway of etc.  Not a huge deal to have onsite move the cable, but an annoyance none the less. After that I said bah-hum-bug, and so they connect to both now, and STP so far has never caused me any grief. ... View more