Module 7 Pre-Assessment

Which protocol automates assignment of IP addresses on a network, and which port number does it use? (Choose two.)

• DHCP

• 80

• DNS

• 67

• SMB

Answer explanation

DNS uses port 53 and translates URLs to IP addresses. SMB provides shared access to files and printers and uses port 445. Port 80 is used by HTTP. HTTP is a protocol used to communicate between a web browser and a server.

Refer to the exhibit. PC1 is configured to obtain a dynamic IP address from the DHCP server. PC1 has been shut down for two weeks. When PC1 boots and tries to request an available IP address, which destination IP address will PC1 place in the IP header?

• 192.168.1.1

• 192.168.1.8

• 192.168.1.255

• 255.255.255.255

A company uses DHCP servers to dynamically assign IPv4 addresses to employee workstations. The address lease duration is set as 5 days. An employee returns to the office after an absence of one week. When the employee boots the workstation, it sends a message to obtain an IP address. Which Layer 2 and Layer 3 destination addresses will the message contain?

• FF-FF-FF-FF-FF-FF and 255.255.255.255

• both MAC and IPv4 addresses of the DHCP server

• MAC address of the DHCP server and 255.255.255.255

• FF-FF-FF-FF-FF-FF and IPv4 address of the DHCP server

Answer explanation

When the lease of a dynamically assigned IPv4 address has expired, a workstation will send a DHCPDISCOVER message to start the process of obtaining a valid IP address. Because the workstation does not know the addresses of DHCP servers, it sends the message via broadcast, with destination addresses of FF-FF-FF-FF-FF-FF and 255.255.255.255.

Which command will allow a network administrator to check the IP address that is assigned to a particular MAC address?

• Router# show ip dhcp binding

• Router# show ip dhcp pool

• Router# show ip dhcp server statistics

• Router# show running-config I section_dhcp

Answer explanation

The show ip dhcp binding command will show the leases, including IP addresses, MAC addresses, lease expiration, type of lease, client ID, and user name.

Which message does an IPv4 host use to reply when it receives a DHCPOFFER message from a DHCP server?

• DHCPACK

• DHCPDISCOVER

• DHCPOFFER

• DHCPREQUEST

Answer explanation

When the client receives the DHCPOFFER from the server, it sends back a DHCPREQUEST broadcast message. On receiving the DHCPREQUEST message, the server replies with a unicast DHCPACK message.

Which command, when issued in the interface configuration mode of a router, enables the interface to acquire an IPv4 address automatically from an ISP, when that link to the ISP is enabled?

• ip dhcp pool

• ip address dhcp

• service dhcp

• ip helper-address

Answer explanation

The ip address dhcp interface configuration command configures an Ethernet interface as a DHCP client. The service dhcp global configuration command enables the DHCPv4 server process on the router. The ip helper-address command is issued to enable DHCP relay on the router. The ip dhcp pool command creates the name of a pool of addresses that the server can assign to hosts.

Which set of commands will configure a router as a DHCP server that will assign IPv4 addresses to the 192.168.100.0/23 LAN while reserving the first 10 and the last addresses for static assignment?

• ip dhcp excluded-address 192.168.100.1 192.168.100.10ip dhcp excluded-address 192.168.100.254ip dhcp pool LAN-POOL-100network 192.168.100.0 255.255.255.0ip default-gateway 192.168.100.1

• ip dhcp excluded-address 192.168.100.1 192.168.100.10ip dhcp excluded-address 192.168.101.254ip dhcp pool LAN-POOL-100network 192.168.100.0 255.255.254.0default-router 192.168.100.1

• dhcp pool LAN-POOL-100ip dhcp excluded-address 192.168.100.1 192.168.100.9ip dhcp excluded-address 192.168.100.254network 192.168.100.0 255.255.254.0default-router 192.168.101.1

• ip dhcp excluded-address 192.168.100.1 192.168.100.9ip dhcp excluded-address 192.168.101.254ip dhcp pool LAN-POOL-100ip network 192.168.100.0 255.255.254.0ip default-gateway 192.168.100.1

Answer explanation

The /23 prefix is equivalent to a network mask of 255.255.254.0. The network usable IPv4 address range is 192.168.100.1 to 192.168.101.254 inclusive. The commands dhcp pool , ip default-gateway , and ip network are not valid DHCP configuration commands.

Which kind of message is sent by a DHCP client when its IP address lease has expired?​

• a DHCPDISCOVER broadcast message

• a DHCPREQUEST broadcast message​

• a DHCPREQUEST unicast message​

• a DHCPDISCOVER unicast message​

Answer explanation

When the IP address lease time of the DHCP client expires, it sends a DHCPREQUEST unicast message directly to the DHCPv4 server that originally offered the IPv4 address.

A host PC is attempting to lease an address through DHCP. What message is sent by the server to let the client know it is able to use the provided IP information?

• DHCPDISCOVER

• DHCPOFFER

• DHCPREQUEST

• DHCPACK

• DHCPNACK

Answer explanation

When a host uses DHCP to automatically configure an IP address, the typically sends two messages: the DHCPDISCOVER message and the DHCPREQUEST message. These two messages are usually sent as broadcasts to ensure that all DHCP servers receive them. The servers respond to these messages using DHCPOFFER, DHCPACK, and DHCPNACK messages, depending on the circumstance.

What is a result when the DHCP servers are not operational in a network?

• Workstations are assigned with the IP address 0.0.0.0.

• Workstations are assigned with the IP address 127.0.0.1.

• Workstations are assigned with IP addresses in the 10.0.0.0/8 network.

• Workstations are assigned with IP addresses in the 169.254.0.0/16 network.

Answer explanation

When workstations are configured with obtaining IP address automatically but DHCP servers are not available to respond to the requests, a workstation can assign itself an IP addresses from the 169.254.0.0/16 network.