Extended Ping: The Missing Return Route
Ping says the path works. Users say it does not. Change one ping option and find the router that has no way back, live, right below.
Symptom
A plain ping works and users still cannot reach the far side. One ping option exposes a router that has no way to send the replies back.
Your mission
Inspect, recover, then verify
Format
Cisco IOS CLI
Investigate before you configure.
Use the CLI evidence to isolate the fault, make the smallest safe correction, then verify the network state changed.
Observe the symptom and link state.
Diagnose by comparing the protocol evidence.
Verify the expected device state and confirm the original symptom is resolved.
Console access: R1 · R2
This workspace stacks for portrait phones. Rotate to landscape for the full split-screen console.
Need a hint?
Reveal the root cause when you're ready.
Try the investigation first, then use this as your escape hatch, not a dead end.
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Lab debrief
Turn the session into a repeatable troubleshooting pattern.
Use this reference after your attempt: first explain the symptom, then verify the evidence, then confirm the repair.
The problem
Hosts behind R1 cannot reach services behind R2. An engineer pinged R2's loopback from R1, got five replies, and declared the network healthy.
What you'll practice
- Explain which source address a plain router ping uses
- Run an extended ping sourced from a LAN-facing interface
- Use traceroute to confirm the forward path
- Find a missing return route with show ip route on the far router
The topology
R1 and R2 share 10.0.12.0/24 on Ethernet0/0. R1's Loopback0 (1.1.1.1) represents its user LAN and R2's Loopback0 (2.2.2.2) represents the service. R1 has a default route toward R2.
Commands to run yourself
The real diagnostic commands for this lab, copy-paste ready. Run these in the same order to reproduce the investigation on your own session.
ping 2.2.2.2ping 2.2.2.2 source loopback0traceroute 2.2.2.2 numericshow ip route 1.1.1.1Topology diagram
Fact-checked references
The commands and behaviour in this lab were checked against these primary references.
Frequently asked
Why did the first ping succeed?
A router's ping uses the address of the interface it leaves through, here 10.0.12.1. R2 is directly connected to that subnet, so it can always reply. The users' traffic comes from a different network, and only a ping sourced from that network tests the same return path.
Is extended ping a different command?
No. It is ping with extra options. You can answer its prompts interactively after typing ping on its own, or give the options on one line, as in ping 2.2.2.2 source loopback0.
Why does traceroute look healthy?
Traceroute from R1 is also sourced from 10.0.12.1 by default, and the replies come from R2's own interface. It confirms the forward path but, like the plain ping, never tests the route back to the LAN.
Ready to run this lab yourself?
No setup, no image sourcing. Book a session or ask for a live demo.