300-410 Layer 3 Technologies Practice Question
A network engineer is configuring a GRE tunnel between two Cisco routers across an ISP network. The tunnel source is GigabitEthernet0/0 (IP 203.0.113.1) and the tunnel destination is 203.0.113.2. The engineer notices that the tunnel interface is up, but no traffic is passing through it. The engineer suspects a routing issue. Which command should be used to verify that the tunnel endpoint is reachable?
⚠ Common exam trap
The trap here is assuming that a tunnel interface being up/up guarantees end-to-end connectivity, when in fact the tunnel can be up even if the destination is unreachable, especially without keepalives.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
ping 203.0.113.2 source 203.0.113.1
To verify reachability to the tunnel destination, you should ping the destination IP address using the tunnel source address as the source. This tests the underlying transport network and ensures that the tunnel endpoint is reachable. Other commands like show ip interface brief or show interface tunnel only show local status, and traceroute may not use the correct source address.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
ping 203.0.113.2 source 203.0.113.1
Why this is correct
This command sends an ICMP echo request to the tunnel destination (203.0.113.2) using the tunnel source address (203.0.113.1) as the source. If the ping succeeds, the tunnel endpoint is reachable, and the underlying transport network is working. If it fails, there is a routing or connectivity issue between the endpoints, which would prevent the tunnel from passing traffic. This is the correct way to test reachability to the tunnel destination.
- ✗
show interface tunnel 0
Why it's wrong here
The show interface tunnel 0 command displays detailed statistics and status of the tunnel interface, including line protocol status and encapsulation. While it can show if the tunnel is up, it does not test reachability to the tunnel destination. The tunnel can be up even if the destination is unreachable in some cases, depending on the tunnel type and keepalives. This command is useful for checking interface counters and errors, but not for verifying end-to-end reachability.
- ✗
traceroute 203.0.113.2
Why it's wrong here
A traceroute to the tunnel destination would show the path taken to reach 203.0.113.2, which can help identify where the path breaks. However, it does not use the tunnel source address as the source, so the results might not reflect the actual path taken by tunneled packets if the router uses a different source address for traceroute. The more direct and specific test is to ping with the source address, which simulates the tunnel traffic.
- ✗
show ip interface brief
Why it's wrong here
The show ip interface brief command provides a summary of interface status and IP addresses, including the tunnel interface. It can confirm that the tunnel interface is up/up, but it does not verify reachability to the tunnel destination. It only shows local interface status. To verify reachability to the remote tunnel endpoint, you need to test connectivity to the destination IP address.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.