VLAN detective
Same two-switch network: Sales in VLAN 10 (192.168.10.0/24), HR in VLAN 20 (192.168.20.0/24), PC1 and PC2 on SW1, PC3 and PC4 on SW2, and a trunk on Gi0/1 with native VLAN 99. After a weekend change, PC1 can't reach PC3 and PC2 can't reach PC4. Find every fault and fix it. Don't change the PCs.
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.
Solution explanation
Four faults: SW1's trunk only allowed VLANs 20 and 99, so VLAN 10 never crossed (fixed with allowed vlan add 10, not by replacing the list); SW2 had no VLAN 20 at all; SW2's Fa0/2 was in VLAN 10 instead of 20; and SW2's native VLAN was 1 while SW1's was 99 (CDP's native VLAN mismatch message was the clue). show interfaces trunk and show vlan brief on both switches find all four.
Show solution
[SW1]
enable
show interfaces trunk
[SW2]
enable
show vlan brief
show interfaces trunk
configure terminal
vlan 20
name HR
interface fa0/2
switchport access vlan 20
interface g0/1
switchport trunk native vlan 99
end
[SW1]
configure terminal
interface g0/1
switchport trunk allowed vlan add 10
end
[PC1]
ping 192.168.10.12
[PC2]
ping 192.168.20.12