How to distinguish physical interface and logical interface(subinterface) in Cisco Router/Switch? Can you please specify a formal way for this if have?
A physical interface will be numbered with the same interface name as is printed on the physical port. For example "GigabitEthernet 0/1" corresponds to port 1 on module 0 (or the base unit).
A logical interface can be a subinterface on a routed port and will have a dot (".") preceding the subinterface number (ex. GigabitEthernet 0/1.1). It can also be a loopback or virtual interface (on a router this could also include interfaces like tunnel and virtual tunnel or VTI types). A switch can also have VLAN type logical interfaces (e.g. interface vlan 1) which are used as layer 3 virtual interfaces.