(The network orientation of the router address is more complex, and it can be located on the edge of the internal subnet or on the edge of the internal and external networks. At the same time, in order to achieve strong applicability, it needs to connect to various networks, so its interfaces must be diverse. For these, not to mention ordinary network enthusiasts, even many network administrators can't explain clearly. To this end, the author will give you a comprehensive introduction to the various interfaces and connection methods of the router.)