Module 10

Question 1

Q19-11 Explain why the internet does not create a report message to report the error in an IP datagram that carries an ICMPv4 message.

Answer 1

If this happens, we may enter a loop, a vicious circle. The first datagram is in
error; the second datagram reports error in the first. If the second datagram is
also in error, the third datagram will be carrying error information about the
second, and so.

Question 2

Explain how the address resolution protocol (ARP) translates an IP address to its corresponding physical address.

Answer 2

At a router, it decides the IP address of the next-hop to forward a received IP packet, by using the routing table with the IP destination address in the packet.
IP address of the next-hop must be translated to the MAC address (L2 physical address), so that the packet can be forwarded to the next-hop through the data link layer and the physical layer.

Address resolution protocol (ARP) is used for the address resolution.

An initial ARP request is sent out as a broadcast.

An ARP reply is sent back unicast.

Question 3

List the types of error messages supported by Internet Control Message Protocol (ICMP).

Answer 3

• Destination unreachable
• Source quench
• Time exceeded