ICMP

Question 1

What is the purpose of ICMP?

Answer 1

Reports errors in network communication.
Diagnoses network issues.
Operates within the IP layer to manage and control device communication.

Question 2

What are the main fields in an ICMP message?

Answer 2

Type (1 byte): Specifies the message type.
Code (1 byte): Provides sub-type details.
Checksum (2 bytes): Validates message integrity.
Data: Contains additional information based on the message type.

Question 3

What is the purpose of ICMP Echo Request/Reply messages?

Answer 3

Type 8, Code 0 (Request): Asks the
send an identical message back (echo).

Type 0, Code 0 (Reply): Responds with the requested message.
Commonly used by the ping command to test connectivity and measure round-trip time.

Question 4

What does an ICMP Destination Unreachable message indicate?

Answer 4

Type 3 messages signal issues reaching the destination. Common codes include:

Code 0: Network unreachable.
Code 1: Host unreachable.
Code 2: Protocol unreachable.
Code 3: Port unreachable.
Code 6: Network unknown.
Code 7: Host unknown.

Question 5

What is the role of an ICMP Redirect message?

Answer 5

Type 5, Code 0: Informs the sender of a better route to the destination.
Provides the next router in the optimal path.

Question 6

When is an ICMP Time Exceeded message used?

Answer 6

Type 11, Code 0: Indicates that the packet’s hop limit (TTL) reached zero, causing the packet to be dropped.

Question 7

What does an ICMP Parameter Problem message indicate?

Answer 7

Type 12, Code 0: Signals an invalid or incomplete IP header in the packet.

Question 8

How do ICMP Router Advertisement and Discovery messages work?

Answer 8

Type 9 (Advertisement): Routers announce their presence to hosts.
Type 10 (Discovery): Hosts search for routers actively.

Question 9

How does the ping command utilize ICMP?

Answer 9

Sends an Echo Request (Type 8) to a target.
Waits for an Echo Reply (Type 0) to verify connectivity and measure round-trip time.

Question 10

What is the process behind the traceroute tool?

Answer 10

Sends packets with incrementing hop limits (TTL).
Routers decrement the TTL and return an ICMP Time Exceeded message when it reaches zero.
Repeats until the destination is reached, revealing the path taken.