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Troubleshoot — the ping goes out and nothing comes back
Enterprise Intermediate 4 devices 3 checked tasks 100 points Plan lab
PC1 pings PC2 across two routers and times out. R1 has a route to PC2’s LAN. Packets can leave but the replies have no way home. The classic one-way route: work out which router is missing what, from the traceroute and the routing tables, and add exactly that. 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
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The scenario
PC1 pings PC2 across two routers and times out. R1 has a route to PC2’s LAN. Packets can leave but the replies have no way home. The classic one-way route: work out which router is missing what, from the traceroute and the routing tables, and add exactly that.
Your role: a network engineer on the enterprise team. Level: Intermediate Done when: all 3 goals show as passed (100 points).
Network status
Devices: 2 routers, 2 PCs, 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 10.0.12.1/30) and static routes already configured. R2 starts with addresses (G0/0 10.0.2.1/24, G0/1 10.0.12.2/30). PC1 is a host with 10.0.1.10/24, gateway 10.0.1.1. PC2 is a host with 10.0.2.10/24, gateway 10.0.2.1. 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
R2 has a route to PC1’s LAN via R1 (40 pts) PC1 reaches PC2 (40 pts) PC2 reaches PC1 (20 pts) The activity, in order
R2 has a route to PC1’s LAN via R1 Why: The next hop must be an address on a directly connected subnet, or the route never enters the table. Verify with: show ip route PC1 reaches PC2 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 PC2 reaches PC1 Why: A ping needs a route in BOTH directions. This is the end-to-end proof that everything before it worked. Verify with: ping 10.0.1.10 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: Adding a route on the router that already works Common mistake: A default route pointing the wrong way Common mistake: Not testing the reverse direction Why this matters
Routing is two one-way trips. A ping that goes out and never returns is the classic missing-return-route fault: the far router has no path back to the source network.
What you will be able to do
Use traceroute to find where a packet stops
Read both routing tables and spot the asymmetric path
Add exactly the route that is missing
The network
ISR 2911, PC — 4 devices in all, already cabled.
Gi0/1 10.0.12.1/30 Gi0/1 10.0.12.2/30 Fa0 Gi0/0 10.0.1.1/24 Fa0 Gi0/0 10.0.2.1/24 R1 R2 PC1 10.0.1.10/24 · gw 10.0.1.1 PC2 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 R2 ISR 2911 configure it PC1 PC 10.0.1.10 / 255.255.255.0 gw 10.0.1.1 PC2 PC 10.0.2.10 / 255.255.255.0 gw 10.0.2.1
Cabling
R1 Gi0/1 ↔ R2 Gi0/1 PC1 Fa0 ↔ R1 Gi0/0 PC2 Fa0 ↔ R2 Gi0/0
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 10.0.12.1 255.255.255.252
no shutdown
exit
ip route 10.0.2.0 255.255.255.0 10.0.12.2 R2 interface g0/0
ip address 10.0.2.1 255.255.255.0
no shutdown
exit
interface g0/1
ip address 10.0.12.2 255.255.255.252
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 R2 has a route to PC1’s LAN via R1 40 On R2: show ip route 10.0.1.0 shows next hop 10.0.12.1. 2 PC1 reaches PC2 40 On PC1: ping 10.0.2.10 must succeed. 3 PC2 reaches PC1 20 On PC2: ping 10.0.1.10 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
Adding a route on the router that already works
A default route pointing the wrong way
Not testing the reverse direction
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:
R2 ip route 10.0.1.0 255.255.255.0 10.0.12.1 Where this is examined
CCNA (static routing), Network+ (routing problems), CCNP ENARSI (troubleshooting).
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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