Practice / Scenarios

Local Ping Works, Remote Network Fails

beginner
LAB TOPOLOGY

Router-on-a-Stick Lab

One 802.1Q trunk · router subinterfaces as gateways

ACCESS VLAN 10NICE0/1ACCESS VLAN 20NICE0/3802.1Q TRUNKE0/0E0/0PC1VLAN 10192.168.10.10/24PC2VLAN 20192.168.20.10/24SW1Layer-2 SwitchR1802.1Q SubinterfacesE0/0.10 .254 · E0/0.20 .254

Situation

PC1 192.168.10.10/24 can ping 192.168.10.20, but cannot ping 192.168.20.10. The router interface for VLAN 10 is 192.168.10.254, while PC1’s gateway is mistakenly 192.168.10.1.

Your task

Why does local communication still work? At what exact point does remote communication fail?

Reasoning

For a local destination, PC1 ARPs for the destination host directly. For a remote destination, PC1 must send the frame to its default gateway. The wrong gateway breaks that next-hop step.

Verify

Check host IP/mask/gateway, ping the configured gateway, then ping the real gateway. Fix the gateway and retest before touching router routes.