How it works
How devices are physically cabled and how they are logically grouped are separate questions. Two devices on the same switch can sit in different logical networks, and devices in different rooms can share one.
When reading a diagram, decide which kind it is. A physical diagram answers questions about cables and failure points; a logical one answers questions about reachability.
Common error
Assuming physical proximity implies logical grouping is one of the most common misreadings of a network diagram.
Worked example
Compare a cable drawing with logical groups on the same switch.
Evidence
Physical: one switch, two classrooms
Room A ports: staff VLAN
Room B ports: student VLAN
Printer: staff VLANPhysical proximity does not determine logical reach. Staff and student ports can share the same switch while belonging to different VLANs. The physical diagram locates cabling and failure points; the logical diagram should show VLANs, subnets, gateways, and permitted crossings.
Exercises
3.2.1
Two devices are in different rooms but use the same VLAN and subnet. Must their traffic cross an IP router solely because of the room boundary?
Show solution
No. Room location alone does not create an IP boundary. Their logical configuration, link connectivity, and switching path determine whether direct local communication is possible.
3.2.2
A switch failure disconnects both staff and students despite VLAN separation. What does this reveal about logical isolation and physical resilience?
Show solution
Logical isolation can separate traffic without providing independent hardware. Both groups still share the switch as a physical failure point; resilience requires an appropriate additional physical path or device.