Having two ports transparently pass traffic between one another?

Hey there,

I wasn't really sure how to word the title of this post properly, but essentially I'm looking to have my managed switch 'transparently' connect two of its ports together. The switch is a D-Link DGS-1510-28X.

Essentially the issue I'm having is that my Wired internet connection provided by my university will errdisable the port upstream if I connect any form of switch to it. I'm assuming this is something to do with STP? Would also be interesting if anyone could explain how this works and how the upstream switch detects that another switch has been connected to it. The upstream switches are Cisco 2960-Xs. The connection does not require 802.1X or any form of authentication.

What I'd like to achieve is having the connection from my university come in on Port 1 of my DGS-1510-28X, then have two other computers on ports 2 and 3. I'd like to be able to switch between which machine out of port 2 and port 3 is connected to the internet via port one using the switch itself, rather than physically changing cables. I don't need the connections between the two machines and ports 2 and 3 to carry LAN traffic, they've both got two interfaces and will be connected to the switch on other ports for LAN traffic, this is purely for WAN traffic.

I'm not sure if this is possible at all, but if so, some explanation or a starting point would be useful. If this isn't possible, then I'd greatly appreciate any ideas or suggestions as to how I could go about toggling my connection between these two hosts using a script. My next idea after this is to build a physical switch using an Arduino and some analog multiplexers, but that seems all a bit overkill if there's a better way I can do this.

Cheers!