Physical layer detective
A small campus has three separate physical faults. PC1 must be able to reach both PC2 and PC3, and every link must be clean (up, matching speed and duplex, no errors). Use the port lights, show interfaces status, show interfaces and the cable popover to find each fault, then fix it from the console or by replacing the cable.
How it works: this is VulnTech NetLab, a network simulator running in your browser. Click a device in the diagram to open its console and type commands, just like on real equipment (? shows help, Tab finishes a word). Click a cable to inspect it. Tasks tick themselves off as you complete them; questions are answered in the box under each task. Your work is kept if you reload; Reset starts the network over.
Hints
Red dots mean no link. A green link can still be faulty: check its counters.
Click any cable to inspect it and replace it.
Solution explanation
Fault 1: PC2 used a crossover cable on a port where no mdix auto was set, so neither end could swap its pins. mdix auto fixes it (so would a straight-through cable). Fault 2: the switches have LX optics, which need single-mode fibre, but a multimode cable was fitted, so the uplink stayed down. Fault 3: PC3's copper run was 150 m, beyond the 100 m limit, so frames arrived with CRC errors; a shorter run fixed it.
Show solution
[SW1]
enable
show interfaces status | include Port|Fa0/2_|Gi0/1
show running-config interface fa0/2
configure terminal
interface fa0/2
mdix auto
end
@cable SW1 g0/1 smf 300
[SW2]
enable
show interfaces fa0/3 | include CRC
@cable SW2 fa0/3 straight 50
[PC1]
ping 192.168.1.12
ping 192.168.1.13