Difficulty: Easy
Correct Answer: 2 and 3
Explanation:
Introduction / Context:
ICMP communicates network errors and informational messages among IP hosts and routers. Accurately distinguishing ICMP's capabilities and its encapsulation helps interpret diagnostics like ping and traceroute and avoid incorrect assumptions about reliability.
Given Data / Assumptions:
Concept / Approach:
ICMP is neither a reliable transport nor a session protocol; it is carried directly by IP (protocol number 1). It signals problems such as unreachable destinations and TTL expiry, which informs hosts and applications of network issues.
Step-by-Step Solution:
Verification / Alternative check:
Protocol number reference: ICMP = 1, TCP = 6, UDP = 17. Tools like tcpdump/Wireshark show ICMP directly inside IP, never inside UDP.
Why Other Options Are Wrong:
1 only / 1 and 4 / All of the above: These include statement #1 or #4, both incorrect. ICMP offers no delivery guarantees and is not encapsulated in UDP.
Common Pitfalls:
Assuming any control messaging implies reliability; also confusing ICMP Echo Reply with a transport-layer acknowledgment.
Final Answer:
2 and 3
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