Difficulty: Easy
Correct Answer: 3 and 4
Explanation:
Introduction / Context:
ICMP (Internet Control Message Protocol) is used by IP devices to send control and error messages, such as “destination unreachable” or “time exceeded.” Understanding what ICMP does and does not do is essential for interpreting ping/traceroute results and diagnosing Layer-3 problems.
Given Data / Assumptions:
Concept / Approach:
ICMP is a companion to IP for signaling errors and informational events. It is not a transport protocol and does not provide reliability guarantees or TCP-style acknowledgments. ICMP messages are carried inside IP packets (protocol number 1).
Step-by-Step Solution:
Verification / Alternative check:
Ping uses ICMP Echo Request/Reply encapsulated in IP. Traceroute observes ICMP Time Exceeded responses. Neither mechanism acknowledges TCP segments nor guarantees delivery.
Why Other Options Are Wrong:
1 only / 2 and 3 / 2, 3 and 4: Any option including #1 or #2 is invalid because ICMP neither acknowledges TCP nor provides reliability guarantees.
Common Pitfalls:
Confusing ICMP replies (Echo Reply) with TCP ACKs; assuming “control” implies reliability. ICMP itself may be filtered by firewalls, further undermining any notion of delivery guarantees.
Final Answer:
3 and 4
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