7. Network Layer (2)

Question 1

What protocol is used to map IP addresses to MAC addresses in a local network?

Answer 1

Address Resolution Protocol (ARP)

Question 2

What type of message does ARP send to find the MAC address of a host?

Answer 2

ARP sends a broadcast query message asking “Who is the owner of this IP?”

Question 3

True or False: ARP replies are broadcast messages sent to all hosts in the network.

Answer 3

False

Question 4

How does an ARP reply message differ from an ARP request?

Answer 4

An ARP reply is a unicast message directly sent to the requester with the MAC address

Question 5

What is stored in an ARP Cache?

Answer 5

Recent mappings of IP addresses to MAC addresses

Question 6

What is a Gratuitous ARP?

Answer 6

An ARP reply sent without a preceding request

Question 7

Give two use cases for Gratuitous ARP.

Answer 7

Updating ARP mappings after a MAC address change and announcing a host’s presence when it joins a network.

Question 8

What happens when an ARP request is made for a non-existing host?

Answer 8

Several ARP requests are sent with increasing intervals; if no reply is received

Question 9

What is Proxy ARP?

Answer 9

When a node replies to an ARP request on behalf of another node

Question 10

True or False: The destination MAC address in an ARP query frame is the broadcast address FF:FF:FF:FF:FF:FF.

Answer 10

True

Question 11

Why is ARP vulnerable to attacks such as ARP poisoning?

Answer 11

Because ARP does not authenticate requests or replies and updates the ARP cache immediately upon receiving packets

Question 12

What is the primary function of the Internet Control Message Protocol (ICMP)?

Answer 12

To send error messages and operational information about network problems back to the sender.

Question 13

Which ICMP message type is used to check if a host is reachable (ping)?

Answer 13

Type 8 — Echo request

Question 14

What does an ICMP Destination Unreachable message indicate?

Answer 14

That the destination host or network cannot be reached

Question 15

How is trace route functionality implemented using ICMP?

Answer 15

By sending packets with increasing TTL values; routers send back ICMP Time Exceeded messages when TTL reaches zero

Question 16

True or False: ICMP messages are encapsulated inside TCP segments.

Answer 16

False

Question 17

How are ICMP messages encapsulated?

Answer 17

Inside IP packets

Question 18

What are some common security issues related to ICMP?

Answer 18

ICMP can be exploited for denial-of-service attacks by sending spoofed echo requests or destination unreachable messages.

Question 19

What is the main motivation for introducing IPv6?

Answer 19

To address the scarcity of IPv4 addresses

Question 20

How long is an IPv6 address

Answer 20

and how is it represented?

Question 21

What abbreviation rules apply to IPv6 addresses?

Answer 21

Leading zeros in each block can be omitted; consecutive blocks of zeros can be replaced by “::” but only once per address.

Question 22

Name the three types of IPv6 addresses.

Answer 22

Unicast

Question 23

Does IPv6 support broadcasting?

Answer 23

No

Question 24

What is the prefix for global unicast IPv6 addresses?

Answer 24

2000::/3

Question 25

What are Link-Local IPv6 addresses used for?

Answer 25

Communication within a single local network segment; they cannot be routed outside the local link.

Question 26

What is the prefix for IPv6 Link-Local addresses?

Answer 26

FE80::/10

Question 27

What key header fields are removed or omitted in IPv6 compared to IPv4 to improve performance?

Answer 27

Header checksum

Question 28

What mechanism does IPv6 use to extend header options?

Answer 28

A linked list of extension headers with the Next Header field pointing to the next header or protocol.