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Q3. Which of the following utilities use ICMP? [Select 2]
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A. FTP B. traceroute C. ping D. telnet
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Correct answer: B,C
Explanation:
Internet Control Message Protocol (ICMP) messages are delivered in IP packets. ICMP messages are used for out-of-band messages related to network operation or errors. Since ICMP uses IP, ICMP packet delivery is unreliable.
Some of the functions fulfilled by ICMP include the following:
1. Announce network errors.
2. Announce network congestion.
3. Assist Troubleshooting. ICMP supports an Echo function, which just sends a packet on a round--trip between two hosts. Ping, a common network management tool, is based on this feature. Ping will transmit a series of packets, measuring average round--trip times and computing loss percentages.
4. Announce Timeouts. If an IP packet's TTL field drops to zero, the router discarding the packet normally generates an ICMP packet announcing this fact. TraceRoute is a tool which maps network routes by sending packets with small TTL values and watching the ICMP timeout announcements.
Note that telnet, and ftp use TCP, and are considered reliable.
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