LFCS Networking Practice Question
A server on a corporate network is intermittently losing connectivity. The administrator runs 'tcpdump -i eth0 icmp' and sees 'ICMP time exceeded in-transit' messages from a router. What is the most likely cause?
⚠ Common exam trap
Linux Foundation often tests the distinction between ICMP error types, and the trap here is that candidates confuse 'time exceeded' with 'destination unreachable' or assume any connectivity loss is due to a firewall or MTU issue, rather than recognizing the specific TTL exhaustion symptom.
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
✓
There is a routing loop or the TTL is too low.
The 'ICMP time exceeded in-transit' message indicates that a packet's TTL (Time to Live) has reached zero before reaching its destination. This is most commonly caused by a routing loop, where packets circulate endlessly between routers, or by an initial TTL value that is too low for the number of hops required. The router that decrements the TTL to zero sends this ICMP Type 11 Code 0 message back to the source, as defined in RFC 792.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
There is a mismatch in MTU size.
Why it's wrong here
MTU issues cause 'fragmentation needed' messages.
- ✗
The destination host is down.
Why it's wrong here
That would produce 'destination unreachable' messages.
- ✗
A firewall is blocking the packets.
Why it's wrong here
Firewalls typically drop packets silently or send 'administratively prohibited'.
- ✓
There is a routing loop or the TTL is too low.
Why this is correct
'Time exceeded' indicates TTL expired, common in loops.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This LFCS practice question is part of Courseiva's free Linux Foundation 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 LFCS exam.