I'm trying to sort out a networking issue that had me scratching my head this afternoon. I have two buildings in question, building A and B. Building A gets its internet connection from a nearby office via an ethernet drop. The switch in the office is a Ubiquiti 24 port unit. Building B gets its network from an ethernet drop from building A.
Office----Building A ----- Building B
Today I was at Building A and doing some cleanup and upgrades on in their small wall rack which included switching out an old gigabit unmanaged switch to a Unifi USW-16-POE. Building B's ethernet drop goes into a cabinet that has a couple of SLC/Scada items attached to a small switch that I believe is also managed but I can't remember the name/brand of the unit, but it does basic switching as expected.
Essentially what is happening is if I connect the drop that goes to Building B into the new Unifi Switch in Building A, both sides of the connection die. All AP's, anything wired with ethernet will go to a 169 IP. I disconnected everything that wasn't SCADA related in building B but nothing changed. After several confusing hours I decided to hook the old unmanaged switch back up in Building A and everything went back to working normally. I even connected the new unifi switch into the unmanaged switch and it all still worked.
I'm just trying to understand what's going on when I connect the drop to building B to cause everything in A and B to quit suddenly when it's connected to the new managed switch. I've left all the STP/RSTP settings to their default values on the new switch since I haven't had a problem before, and I don't know if it's a problem now. Any help would be greatly appreciated.
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