9.4.2 Module Quiz – Address Resolution
1. Which destination address is used in an ARP request frame?
- 0.0.0.0
- 255.255.255.255
- FFFF.FFFF.FFFF
- 127.0.0.1
- 01-00-5E-00-AA-23
Explanation: The purpose of an ARP request is to find the MAC address of the destination host on an Ethernet LAN. The ARP process sends a Layer 2 broadcast to all devices on the Ethernet LAN. The frame contains the IP address of the destination and the broadcast MAC address, FFFF.FFFF.FFFF.
2. What addresses are mapped by ARP?
- destination MAC address to a destination IPv4 address
- destination IPv4 address to the source MAC address
- destination IPv4 address to the destination host name
- destination MAC address to the source IPv4 address
Explanation: ARP, or the Address Resolution Protocol, works by mapping a destination MAC address to a destination IPv4 address. The host knows the destination IPv4 address and uses ARP to resolve the corresponding destination MAC address.
3. What will a Layer 2 switch do when the destination MAC address of a received frame is not in the MAC table?
- It initiates an ARP request.
- It broadcasts the frame out of all ports on the switch.
- It notifies the sending host that the frame cannot be delivered.
- It forwards the frame out of all ports except for the port at which the frame was received.
Explanation: A Layer 2 switch determines how to handle incoming frames by using its MAC address table. When an incoming frame contains a destination MAC address that is not in the table, the switch forwards the frame out all ports, except for the port on which it was received.
4. Which two ICMPv6 messages are used during the Ethernet MAC address resolution process? (Choose two.)
- router solicitation
- router advertisement
- neighbor solicitation
- neighbor advertisement
- echo request
Explanation: IPv6 uses neighbor solicitation (NS) and neighbor advertisement (NA) ICMPv6 messages for MAC address resolution.
5. Which router component holds the routing table, ARP cache, and running configuration file?
- RAM
- Flash
- NVRAM
- ROM
Explanation: The routing table, ARP cache, and running configuration file are stored in volatile RAM.
6. What type of information is contained in an ARP table?
- switch ports associated with destination MAC addresses
- domain name to IP address mappings
- routes to reach destination networks
- IP address to MAC address mappings
Explanation: ARP tables are used to store mappings of IP addresses to MAC addresses. When a network device needs to forward a packet, the device knows only the IP address. To deliver the packet on an Ethernet network, a MAC address is needed. ARP resolves the MAC address and stores it in an ARP table.
7. A PC is configured to obtain an IP address automatically from network 192.168.1.0/24. The network administrator issues the arp –a command and notices an entry of 192.168.1.255 ff-ff-ff-ff-ff-ff. Which statement describes this entry?
- This is a static map entry.
- This is a dynamic map entry.
- This entry refers to the PC itself.
- This entry maps to the default gateway.
Explanation: The IP address of 192.168.1.255 on the 192.168.1.0/24 network is the broadcast address, which is statically mapped to ff-ff-ff-ff-ff-ff in the ARP table.
8. A cybersecurity analyst believes an attacker is spoofing the MAC address of the default gateway to perform a man-in-the-middle attack. Which command should the analyst use to view the MAC address a host is using to reach the default gateway?
- ipconfig /all
- route print
- netstat -r
- arp -a
Explanation: ARP is a protocol used with IPv4 to map a MAC address to an associated specific IP address. The command arp -a will display the MAC address table on a Windows PC.
9. What is a function of ARP?
- resolving MAC addresses to IPv4 addresses
- resolving port addresses to MAC addresses
- resolving MAC addresses to port addresses
- resolving IPv4 addresses to MAC addresses
Explanation: Resolving IPv4 addresses to MAC addresses is one function of ARP. ARP is also responsible for maintaining the ARP table.
10. What is the purpose of ARP in an IPv4 network?
- to forward data onward based on the destination IP address
- to obtain a specific MAC address when an IP address is known
- to forward data onward based on the destination MAC address.
- to build the MAC address table in a switch from the information that is gathered.
Explanation: ARP performs two functions:
- To obtain a specific MAC address when an IP address is known, by broadcasting an ARP request message to all devices on a particular Ethernet network
- To use the gathered information to create a viewable table of IP address to MAC address mappings
11. Which action is taken by a Layer 2 switch when it receives a Layer 2 broadcast frame?
- It drops the frame.
- It sends the frame to all ports except the port on which it received the frame.
- It sends the frame to all ports that are registered to forward broadcasts.
- It sends the frame to all ports.
Explanation: When a Layer 2 switch receives a frame with a broadcast destination address, it floods the frame to all ports except the port on which it received the frame.
12. When an IP packet is sent to a host on a remote network, what information is provided by ARP?
- the IP address of the destination host
- the IP address of the default gateway
- the MAC address of the router interface closest to the sending host
- the MAC address of the switch port that connects to the sending host
Explanation: When a host sends an IP packet to a destination on a different network, the Ethernet frame cannot be sent directly to the destination host because the host is not directly reachable in the same network. The Ethernet frame must be sent to another device known as the router or default gateway in order to forward the IP packet. ARP is used to discover the MAC address of the router (or default gateway) and use it as the destination MAC address in the frame header.
13. How does the ARP process use an IP address?
- to determine the MAC address of the remote destination host
- to determine the MAC address of a device on the same network
- to determine the amount of time a packet takes when traveling from source to destination
- to determine the network number based on the number of bits in the IP address
Explanation: The ARP process is used to complete the necessary mapping of IP and MAC addresses that are stored in the ARP table that is maintained by each node on a LAN. When the destination device is not on the same network as the source device, the MAC address of the Layer 3 device on the the source network is discovered and added to the ARP table of the source node.
14. The ARP table in a switch maps which two types of address together?
- Layer 3 address to a Layer 2 address
- Layer 3 address to a Layer 4 address
- Layer 4 address to a Layer 2 address
- Layer 2 address to a Layer 4 address
Explanation: The switch ARP table keeps a mapping of Layer 2 MAC addresses to Layer 3 IP addresses. These mappings can be learned by the switch dynamically through ARP or statically through manual configuration.
15. What is one function of the ARP protocol?
- obtaining an IPv4 address automatically
- mapping a domain name to its IP address
- resolving an IPv4 address to a MAC address
- maintaining a table of domain names with their resolved IP addresses
Explanation: The two main functions of the ARP protocol are to resolve an IPv4 address to a MAC address and to maintain an ARP table, which lists the resolved pairs of IPv4 address and MAC address. A device automatically obtains an IP address through DHCP. The functions of DNS include resolving (or mapping) a domain name with its IP address and maintaining a table for the domain name/IP pairs.