Networking Devices and Initial Configuration Module 7.2.3 Address Resolution Quiz Answers
1. Which protocol is used to discover the destination address needed to be added to an Ethernet frame?
- ARP
- DNS
- DHCP
- HTTP
Explanation: In the data link layer, a frame header is added. The frame header includes the source and destination MAC addresses. In order to find the MAC address of the destination host, the sending host uses the Address Resolution Protocol (ARP). If the destination host is not on the same LAN, the MAC address of the default gateway is used as the destination MAC address in the frame header.
2. 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.
3. Refer to the exhibit. PC1 on VLAN 10 wants to communicate with PC2 on VLAN 20. PC1 sends an ARP request to its default gateway, GW1. How does GW1 respond?
- It sends an ARP reply to PC2.
- It sends an ARP request to PC1.
- It forwards the ARP request from PC1 to PC2.
- It sends an ARP reply to PC1 with its own MAC address.
Explanation: GW1 is configured with subinterfaces to accommodate the two different networks related to VLAN10 and VLAN20. If PC1 does not know the MAC address of PC2, PC1 will broadcast an ARP on the VLAN10 network. GW1 will see the broadcast and determine that the IP address of PC2 is on a different network. GW1 will send its MAC address back to PC1.
4. What action does the ARP process take when a host needs to build a frame, but the ARP cache does not contain an address mapping?
- The ARP process sends out an ARP request to the Ethernet broadcast address to discover the IPv4 address of the destination device.
- The ARP process sends out an ARP request to the IPv4 broadcast address to discover the MAC address of the destination device.
- The ARP process sends out an ARP request to the IPv4 broadcast address to discover the IPv4 address of the destination device.
- The ARP process sends out an ARP request to the Ethernet broadcast address to discover the MAC address of the destination device.
Explanation: The address resolution protocol (ARP) maintains a cache of MAC to IPv4 address mappings on the local computer. If there is no mapping in the cache for a specific IPv4 address, then the ARP process sends an Ethernet broadcast on the local link in an attempt to resolve the destination IPv4 address to a MAC address.
5. Which statement describes the treatment of ARP requests on the local link?
- They must be forwarded by all routers on the local network.
- They are received and processed by every device on the local network.
- They are dropped by all switches on the local network.
- They are received and processed only by the target device.
Explanation: One of the negative issues with ARP requests is that they are sent as a broadcast. This means all devices on the local link must receive and process the request.
6. What is the aim of an ARP spoofing attack?
- to flood the network with ARP reply broadcasts
- to fill switch MAC address tables with bogus addresses
- to associate IP addresses to the wrong MAC address
- to overwhelm network hosts with ARP requests
Explanation: In an ARP spoofing attack, a malicious host intercepts ARP requests and replies to them so that network hosts will map an IP address to the MAC address of the malicious host.
7. A cybersecurity analyst believes that an attacker is announcing a forged MAC address to network hosts in an attempt to spoof the default gateway. Which command could the analyst use on the network hosts to see what MAC address the hosts are using to reach the default gateway?
- netsat -r
- route print
- ipconfig /all
- arp -a
Explanation: The command arp -a will display the MAC address table on a PC.
8. What will a host do first when preparing a Layer 2 PDU for transmission to a host on the same Ethernet network?
- It will send the PDU to the router directly connected to the network.
- It will query the local DNS server for the name of the destination host.
- It will search the ARP table for the MAC address of the destination host.
- It will initiate an ARP request to find the MAC address of the destination host.
Explanation: In order to encapsulate a Layer 3 PDU into a frame, the sending host needs to know the MAC address of the destination host. The sending host first checks the ARP table. If a match is found in the table, the host uses the MAC address as the destination MAC in the frame. Otherwise, it will initiate an ARP request to obtain the destination MAC.
9. 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.
10. Which protocol is used by a computer to find the MAC address of the default gateway on an Ethernet network?
- ARP
- TCP
- UDP
- DHCP
Explanation: TCP provides reliable delivery of data. UDP provides unreliable delivery of data. DHCP is used for the automatic assignment of IP addresses. ARP is used to discover the MAC address of a device on the Ethernet network.
11. Refer to the exhibit. PC1 attempts to connect to File_server1 and sends an ARP request to obtain a destination MAC address. Which MAC address will PC1 receive in the ARP reply?
- the MAC address of S1
- the MAC address of the G0/0 interface on R1
- the MAC address of the G0/0 interface on R2
- the MAC address of S2
- the MAC address of File_server1
Explanation: PC1 must have a MAC address to use as a destination Layer 2 address. PC1 will send an ARP request as a broadcast and R1 will send back an ARP reply with its G0/0 interface MAC address. PC1 can then forward the packet to the MAC address of the default gateway, R1.