Broken router-on-a-stick
This router-on-a-stick worked last week: PC1 (VLAN 10, 192.168.10.0/24) and PC2 (VLAN 20, 192.168.20.0/24) could reach each other through R1's subinterfaces Gi0/0.10 and Gi0/0.20 (gateways .1). Now neither PC can even reach its gateway. Find and fix every fault on R1 and SW1.
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
Three faults: R1's physical Gi0/0 was shut down (so both subinterfaces were down too); SW1's Gi0/1 was an access port, so frames left untagged in VLAN 1 and never matched a subinterface; and Gi0/0.20 was set for VLAN 21 instead of 20. After any change, check the subinterface still has its address with show ip interface brief.
Show solution
[R1]
enable
show ip interface brief
show running-config | section interface GigabitEthernet0/0
configure terminal
interface g0/0
no shutdown
interface g0/0.20
encapsulation dot1Q 20
end
[SW1]
enable
show interfaces trunk
configure terminal
interface g0/1
switchport mode trunk
end
[PC1]
ping 192.168.20.10
[PC2]
ping -c 3 192.168.10.10