ARP

Question 1

What does ARP stand for?

Answer 1

Address Resolution Protocol

ARP is used to map logical addresses to physical addresses.

Question 2

What are the two levels of addressing required for packet delivery?

Answer 2

• Logical address
• Physical address

Question 3

What type of address is recognized at the network level?

Answer 3

Logical address

Question 4

What is a physical address?

Answer 4

A local address that should be unique locally but not necessarily universally

Question 5

What is an example of a physical address in Ethernet?

Answer 5

48-bit MAC address

Question 6

What is the purpose of address mapping?

Answer 6

To associate a logical address with its corresponding physical address

Question 7

What are the two types of mapping used in ARP?

Answer 7

• Static mapping
• Dynamic mapping

Question 8

What protocols are used for dynamic mapping?

Answer 8

• Address Resolution Protocol (ARP)
• Reverse Address Resolution Protocol (RARP)

Question 9

True or False: RARP is still widely used in modern networks.

Answer 9

False

Question 10

What happens when a host needs to send an IP datagram to another host?

Answer 10

It must find the physical address of the receiver

Question 11

How does ARP find the physical address of another host?

Answer 11

By sending an ARP query packet

Question 12

What does an ARP query packet include?

Answer 12

• Sender’s physical address
• Sender’s IP address
• Receiver’s IP address

Question 13

How is an ARP query packet transmitted?

Answer 13

It is broadcast over the network

Question 14

What does the ARP response packet contain?

Answer 14

• Recipient’s IP address
• Recipient’s physical address

Question 15

What is the difference between ARP requests and replies?

Answer 15

ARP requests are broadcast; ARP replies are unicast

Question 16

What is the first step in the ARP process when a sender knows the target IP address?

Answer 16

Create an ARP request message

Question 17

In Case 1 of ARP usage, who is the sender?

Answer 17

A host wanting to send a packet to another host on the same network

Question 18

In Case 2 of ARP usage, what does the sender need to do if sending to another network?

Answer 18

Look up the IP address of the next hop router

Question 19

In Case 3 of ARP usage, who is the sender?

Answer 19

A router that has received a datagram destined for a host on another network

Question 20

In Case 4 of ARP usage, what must the sender do if the datagram is destined for a host in the same network?

Answer 20

Map the destination IP address to a physical address

Question 21

Fill in the blank: ARP operates at the ______ layer of the TCP/IP protocol suite.

Answer 21

Data link

Question 22

What is the hardware type field in an ARP packet?

Answer 22

A 16-bit field defining the type of network

Question 23

What is the protocol type field in an ARP packet for IPv4?

Answer 23

0800

Question 24

What does the hardware length field in an ARP packet define?

Answer 24

The length of the physical address in bytes

Question 25

What does the protocol length field in an ARP packet define?

Answer 25

The length of the logical address in bytes

Question 26

What is the encapsulation process for an ARP packet?

Answer 26

An ARP packet is encapsulated directly into a data link frame

Question 27

True or False: Every host on the network processes the ARP query packet.

Answer 27

True

Question 28

What does the type field in an Ethernet frame indicate?

Answer 28

That the data carried by the frame is an ARP packet

Question 29

What is the hardware type in an ARP frame?

Answer 29

0x0001

Question 30

What is the protocol type in an ARP frame?

Answer 30

0x0800

Question 31

How many bytes are in the destination address field of an ARP frame?

Answer 31

6 bytes

Question 32

What does Proxy ARP do?

Answer 32

Acts on behalf of a set of hosts

Question 33

When a router running Proxy ARP receives an ARP request, what does it send?

Answer 33

An ARP reply announcing its own hardware address

Question 34

Fill in the blank: A _______ is an ARP that acts on behalf of a set of hosts.

Answer 34

Proxy ARP

Question 35

What happens when a router receives an IP packet in Proxy ARP?

Answer 35

It sends the packet to the appropriate host or router

Question 36

What is the target for an ARP request when a host is speaking to another host on the same IP network?

Answer 36

The other host's IP address

Question 37

What is the target for an ARP request when speaking to another host on a different IP network?

Answer 37

The Default Gateway’s IP address

Question 38

What is used to cache ARP entries to improve efficiency?

Answer 38

Cache table

Question 39

What states can an ARP cache entry have?

Answer 39

* FREE * PENDING * RESOLVED

Question 40

What does the FREE state in a cache entry indicate?

Answer 40

The time-to-live for this entry has expired

Question 41

What does the PENDING state in a cache entry mean?

Answer 41

A request for this entry has been sent, but the reply has not yet been received

Question 42

What does the RESOLVED state indicate?

Answer 42

The entry now has the physical address of the destination

Question 43

What does the ARP output module do when it receives an IP datagram with a destination in the cache?

Answer 43

Extracts the hardware address and sends the packet to the data link layer

Question 44

What happens when an IP datagram's destination is not found in the cache table?

Answer 44

An entry is added with the state PENDING and an ARP request is sent

Question 45

What action is taken when an ARP input module receives a packet with a target IP address found in the cache?

Answer 45

Changes the state of the entry to RESOLVED and updates the hardware address

Question 46

What happens during the cache-control module's update of entries?

Answer 46

Decrements time-out values and changes states of entries as needed

Question 47

What is done when an entry's attempts exceed the maximum?

Answer 47

The state is changed to FREE, the queue is deleted, and an ICMP message is sent