Internet Control Message Protocol (ICMP) has been designed to compensate _________

A. Error-reporting
B. Error-correction
C. Host and management queries
D. All of the mentioned

Explanation: IP by itself does not provide the features of error reporting or error correction. So, to address these issues a network layer protocol called Internet Control Message Protocol is used. ICMP operates over the IP packet to provide error reporting functionality.

Header size of the ICMP message is _________

A. 8-bytes
B. 8-bits
C. 16-bytes
D. 16-bits

Explanation: An ICMP message has an 8-byte header and a variable size data section. Out of the 8 bytes, the first 4 bytes are of a fixed format having the type, code and checksum fields and the next 4 bytes depend upon the type of the message.

During error reporting, ICMP always reports error messages to ________

A. Destination
B. Source
C. Next router
D. Previous router

Explanation: ICMP notifies the source about the error when an error is detected because the datagram knows information about source and destination IP address. The source can then retransmit the data again or try to correct those errors.

Which of these is not a type of error-reporting message?

A. Destination unreachable
B. Source quench
C. Router error
D. Time exceeded

Explanation: Router error is not a type of error-reporting message in ICMP. The type of error reporting message is specified in the ICMP header. Destination unreachable is type 3 error message, source quench is type 4, and time exceeded is type 11 error message.

ICMP error message will not be generated for a datagram having a special address such as _______

A. 127.0.0.0
B. 12.1.2
C. 11.1
D. 127

Explanation: 127.0.0.0 is a special address known as the loopback address which is used for testing purpose of a machine without actually communicating with a network. Thus no error reporting message will be generated for such special addresses.

When a router cannot route a datagram or host cannot deliver a datagram, the datagram is discarded and the router or the host sends a ____________ message back to the source host that initiated the datagram.

A. Destination unreachable
B. Source quench
C. Router error
D. Time exceeded

Explanation: Router sends destination unreachable message if the destination is not found. Destination unreachable is type 3 error reporting message. It is invoked when the router can’t find a path to the intended destination to forward the packet through.

The source-quench message in ICMP was designed to add a kind of ____________ to the IP.

A. Error control
B. Flow control
C. Router control
D. Switch control

Explanation: Firstly, it informs the source that the datagram has been discarded. Secondly, it warns the source that there is congestion in the network. It’s type 4 error reporting message after which the source is expected to reduce the flow of packets.

In case of time exceeded error, when the datagram visits a router, the value of time to live field is _________

A. Remains constant
B. Decremented by 2
C. Incremented by 1
D. Decremented by 1

Explanation: This field will be decremented by 1 at every router, and will be zero by the time it reaches source. This error reporting message is type 11 and is used to prevent the router from travelling forever in case some unknown path anomaly occurs.

Two machines can use the timestamp request and timestamp replay messages to determine the ___________ needed for an IP datagram to travel between them.

A. Half-trip time
B. Round-trip time
C. Travel time for the next router
D. Time to reach the destination/source

Explanation: The round-trip time refers to the total time taken combining the time taken for a packet sent from a source to reach a destination and the time taken the acknowledgement sent by the destination to reach the source. The Router sends destination unreachable message if the destination is not found.

During debugging, we can use the ____________ program to find if a host is alive and responding.

A. Traceroute
B. Shell
C. Ping
D. Java

Explanation: Ping program is used to find if a host is alive and responding. It is to be entered into a command line with the syntax “ping (IP address)” to be executed. Traceroute is a program used to find the shortest route to the destination IP.