The loopback interface is the loopback port of the router, that is, the software interface. Judging from the product model, most of them do not need to be equipped. The function is, for example, when several routers pass routes to each other, if your routing interface is set as a physical interface, if this physical interface goes down, then the network will be broken, but if you set a loopback port and there are lines reaching routers in other places, then the network will not be broken at this time. For example, bgp generally uses loopback port, and ospf can also be used.