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Troubleshoot — one PC cannot leave its own subnet
Enterprise Beginner 5 devices 3 checked tasks 100 points Free lab
PC1 reaches the server. PC2, on the same switch, cannot. Both can ping each other. Find what is different about PC2 — and prove it from the PC’s own ipconfig before you change anything. You build it in a browser, type real commands at each device, and every task below is
checked against the running configuration — so you find out it is wrong before anybody else does.
Open this lab in the simulator
The simulator runs in your browser with nothing to install. This is a free lab: it stays open on the free plan. It needs an account, which keeps your progress.
The scenario
PC1 reaches the server. PC2, on the same switch, cannot. Both can ping each other. Find what is different about PC2 — and prove it from the PC’s own ipconfig before you change anything.
Your role: a network engineer on the enterprise team. Level: Beginner Done when: all 3 goals show as passed (100 points).
Network status
Devices: 1 router, 1 switch, 2 PCs, 1 server, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. R1 starts with addresses (G0/0 10.0.1.1/24, G0/1 10.0.2.1/24). PC1 is a host with 10.0.1.11/24, gateway 10.0.1.1. PC2 is a host with 10.0.1.12/24, gateway 10.0.1.254. Server is a host with 10.0.2.10/24, gateway 10.0.2.1. SW1 starts with an empty configuration. Known problems
The network worked and now does not: the scenario above says what users report. The cause is a configuration fault, not a cable. Find it with show commands (interfaces, routes, neighbours, running-config) before you change anything; fix only what is wrong. Goals
PC2 uses the router’s address on its own subnet as its default gateway (40 pts) PC2 reaches the server (40 pts) PC1 still reaches the server (20 pts) The activity, in order
PC2 uses the router’s address on its own subnet as its default gateway Why: Reading a show command is the core skill of troubleshooting: the output is the truth, not your configuration. Verify with: ipconfig PC2 reaches the server Why: A ping needs a route in BOTH directions. This is the end-to-end proof that everything before it worked. Verify with: ping 10.0.2.10 PC1 still reaches the server Why: A ping needs a route in BOTH directions. This is the end-to-end proof that everything before it worked. Verify with: ping 10.0.2.10 Tips
Work in the order given: later goals depend on the earlier ones. After every change, run the verify command before moving on; do not guess. Stuck? Read the verify output first. It names the interface, neighbour or route that is wrong. Common mistake: Changing the router when the host is wrong Common mistake: A gateway outside the host’s own subnet Common mistake: Fixing the symptom on one PC while the DHCP pool hands out the same mistake Why this matters
A PC that can reach its own subnet but nothing beyond has a gateway problem more often than anything else. Start at the user, test outward, and read the host’s own configuration before touching a router.
What you will be able to do
Use ipconfig to read address, mask, gateway and DNS
Test gateway, then a remote address, to locate the failing layer
Fix the host without changing a working router
The network
ISR 2911, Catalyst 2960-24TT, PC, Server — 5 devices in all, already cabled.
Fa0/1 Fa0 Fa0/2 Fa0 Gi0/1 Gi0/0 10.0.1.1/24 Gi0/1 10.0.2.1/24 Fa0 R1 SW1 PC1 10.0.1.11/24 · gw 10.0.1.1 PC2 10.0.1.12/24 · gw 10.0.1.254 Server 10.0.2.10/24 · gw 10.0.2.1 Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
R1 ISR 2911 configure it SW1 Catalyst 2960-24TT configure it PC1 PC 10.0.1.11 / 255.255.255.0 gw 10.0.1.1 PC2 PC 10.0.1.12 / 255.255.255.0 gw 10.0.1.254 Server Server 10.0.2.10 / 255.255.255.0 gw 10.0.2.1
Cabling
SW1 Fa0/1 ↔ PC1 Fa0 SW1 Fa0/2 ↔ PC2 Fa0 SW1 Gi0/1 ↔ R1 Gi0/0 R1 Gi0/1 ↔ Server Fa0
What is configured at the start
These are already configured when the lab opens — including, where this is a troubleshooting lab, the fault itself:
R1 interface g0/0
ip address 10.0.1.1 255.255.255.0
no shutdown
exit
interface g0/1
ip address 10.0.2.1 255.255.255.0
no shutdown
exit Tasks, and how each one is checked
Every task is decided by reading the live network — a neighbour in FULL, a ping that succeeds, a line in the running configuration — not by looking for a keyword you typed. The same command shows you what the lab sees.
# Task Pts How to verify it yourself
1 PC2 uses the router’s address on its own subnet as its default gateway 40 On PC2: ipconfig output matches Default Gateway[ .]*: 10\.0\.1\.1\b. 2 PC2 reaches the server 40 On PC2: ping 10.0.2.10 must succeed. 3 PC1 still reaches the server 20 On PC1: ping 10.0.2.10 must succeed.
Stuck? Ask the coach
Tell the coach what you see or what you tried. It gives you a hint, not the answer, the way a senior engineer would. Included with a free trial or any plan.
Ask the coach
Common mistakes
Changing the router when the host is wrong
A gateway outside the host’s own subnet
Fixing the symptom on one PC while the DHCP pool hands out the same mistake
Reference solution
Try it yourself first — the lab checks your work either way. This is one configuration that makes every task pass, device by device:
PC2 netsh interface ip set address "Ethernet" static 10.0.1.12 255.255.255.0 10.0.1.1 Where this is examined
Network+ (troubleshooting methodology), CCNA (IP connectivity).
This lab practises these topics in the zNetLaB certification courses:
Related labs
Where to start
The lessons all guided labs plans
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