CCNA 2 v6 Chapter 8: Check Your Understanding Questions Answers

CCNA 2 v6.0 (Routing & Switching Essentials v6) Chapter 8: DHCP: Check Your Understanding Questions Answers

1. Which DHCPv4 message will a client send to accept an IPv4 address that is offered by a DHCP server?

  • broadcast DHCPACK
  • broadcast DHCPREQUEST
  • unicast DHCPACK
  • unicast DHCPREQUEST

Explanation: When a DHCP client receives DHCPOFFER messages, it sends a broadcast DHCPREQUEST message for two purposes. First, it indicates to the offering DHCP server that it would like to accept the offer and bind the IP address. Second, it notifies any other responding DHCP servers that their offers are declined.

2. Why is the DHCPREQUEST message sent as a broadcast during the DHCPv4 process?

  • For hosts on other subnets to receive the information
  • For routers to fill their routing tables with this new information
  • To notify other DHCP servers on the subnet that the IP address was leased
  • To notify other hosts not to request the same IP address

Explanation: The DHCPREQUEST message is broadcast to inform other DHCP servers that an IP address has been leased.

3. Which address does a DHCPv4 server target when sending a DHCPOFFER message to a client that makes an address request?

  • Broadcast MAC address
  • Client hardware address
  • Client IP address
  • Gateway IP address

Explanation: When a DHCPv4 client does not have an IPv4 address, a DHCPv4 server sends a DHCPOFFER message back to the client hardware address of the requesting DHCPv4 client.

4. As a DHCPv4 client lease is about to expire, what is the message that the client sends the DHCP server?

  • DHCPACK
  • DHCPDISCOVER
  • DHCPOFFER
  • DHCPREQUEST

Explanation: When a DHCP client lease is about to expire, the client sends a DHCPREQUEST message to the DHCPv4 server that originally provided the IPv4 address. This allows the client to request that the lease be extended.

5. What is an advantage of configuring a Cisco router as a relay agent?

  • It can forward both broadcast and multicast messages on behalf of clients.
  • It can provide relay services for multiple UDP services.
  • It reduces the response time from a DHCP server.
  • It allows DHCPDISCOVER messages to pass without alteration.

Explanation: By default, the ip helper-address command forwards the following eight UDP services:

  • Port 37: Time
  • Port 49: TACACS
  • Port 53: DNS
  • Port 67: DHCP/BOOTP client
  • Port 68: DHCP/BOOTP server
  • Port 69: TFTP
  • Port 137: NetBIOS name service
  • Port 138: NetBIOS datagram service

6. An administrator issues the ip address dhcp command on interface G0/1. What is the administrator trying to achieve?

  • Configuring the router to act as a DHCPv4 server
  • Configuring the router to act as a relay agent
  • Configuring the router to obtain IP parameters from a DHCPv4 server
  • Configuring the router to resolve IP address conflicts

Explanation: The ip address dhcp command activates the DHCPv4 client on a given interface. By doing this, the router obtains the IP parameters from a DHCPv4 server.

7. Under which two circumstances would a router usually be configured as a DHCPv4 client? (Choose two.)

  • The administrator needs the router to act as a relay agent.
  • This is an ISP requirement.
  • The router has a fixed IP address.
  • The router is intended to be used as a SOHO gateway.
  • The router is meant to provide IP addresses to the hosts.

Explanation: The ISP frequently requires SOHO routers to be configured as DHCPv4 clients to be connected to the provider.

8. A host on the 10.10.100.0/24 LAN is not being assigned an IPv4 address by an enterprise DHCP server with the address 10.10.200.10/24. What is the best way for the network engineer to resolve this problem?

  • Issue the command default-router 10.10.200.10 at the DHCP configuration prompt on the 10.10.100.0/24 LAN gateway router.
  • Issue the command ip helper-address 10.10.100.0 on the router interface that is the 10.10.200.0/24 gateway.
  • Issue the command ip helper-address 10.10.200.10 on the router interface that is the 10.10.100.0/24 gateway.
  • Issue the command network 10.10.200.0 255.255.255.0 at the DHCP configuration prompt on the 10.10.100.0/24 LAN gateway router.

Explanation: The DHCP server is not on the same network as the hosts, so a DHCP relay agent is required. This is achieved by issuing the ip helper-address command on the interface of the router that contains the DHCPv4 clients to direct DHCP messages to the DHCPv4 server IP address.

9. A company uses the SLAAC method to configure IPv6 addresses for the employee workstations. Which address will a client use as its default gateway?

  • The all-routers multicast address
  • The global unicast address of the router interface that is attached to the network
  • The link-local address of the router interface that is attached to the network
  • The unique local address of the router interface that is attached to the network

Explanation: When a PC is configured to use the SLAAC method for configuring IPv6 addresses, it uses the prefix and prefix-length information that is contained in the RA message, combined with a 64-bit interface ID (obtained by using the EUI-64 process or by using a random number that is generated by the client operating system), to form an IPv6 address. It uses the link-local address of the router interface that is attached to the LAN segment as its IPv6 default gateway address.

10. A network administrator configures a router to send RA messages with M flag as 0 and O flag as 1. Which statement describes the effect of this configuration when a PC tries to configure its IPv6 address?

  • It should contact a DHCPv6 server for all the information that it needs.
  • It should contact a DHCPv6 server for the prefix, the prefix-length information, and an interface ID that is both random and unique.
  • It should use the information that is contained in the RA message and contact a DHCPv6 server for additional information.
  • It should use the information that is contained in the RA message exclusively.

Explanation: ICMPv6 RA messages contain two flags to indicate whether a workstation should use SLAAC, a DHCPv6 server, or a combination to configure its IPv6 address. These two flags are M flag and O flag. When both flags are 0 (by default), a client must use only the information in the RA message. When M flag is 0 and O flag is 1, a client should use the information in the RA message and look for the other configuration parameters (such as DNS server addresses) on DHCPv6 servers.

11. A company implements the stateless DHCPv6 method for configuring IPv6 addresses on employee workstations. After a workstation receives messages from multiple DHCPv6 servers to indicate their availability for DHCPv6 service, which message does it send to a server for configuration information?

  • DHCPv6 ADVERTISE
  • DHCPv6 INFORMATION-REQUEST
  • DHCPv6 REQUEST
  • DHCPv6 SOLICIT

Explanation: In stateless DHCPv6 configuration, a client configures its IPv6 address by using the prefix and prefix length in the RA message, combined with a self-generated interface ID. It then contacts a DHCPv6 server for additional configuration information via an INFORMATION-REQUEST message. The DHCPv6 SOLICIT message is used by a client to locate a DHCPv6 server. DHCPv6 servers use the DHCPv6 ADVERTISE message to indicate their availability for DHCPv6 service. The DHCPv6 REQUEST message is used by a client, in the stateful DHCPv6 configuration, to request all configuration information from a DHCPv6 server.

12. An administrator wants to configure hosts to automatically assign IPv6 addresses to themselves through the use of router advertisement messages, but also to obtain the DNS server address from a DHCPv6 server. Which address assignment method should be configured?

  • RA and EUI-64
  • SLAAC
  • Stateful DHCPv6
  • Stateless DHCPv6

Explanation: Stateless DHCPv6 allows clients to use ICMPv6 router advertisement (RA) messages to automatically assign IPv6 addresses to themselves but then allows these clients to contact a DHCPv6 server to obtain additional information such as the domain name and address of DNS servers. SLAAC does not allow the client to obtain additional information through DHCPv6, and stateful DHCPv6 requires that the client receive its interface address directly from a DHCPv6 server. RA messages, when combined with an EUI-64 interface identifier, are used to automatically create an interface IPv6 address and are part of both SLAAC and stateless DHCPv6.

13. How does an IPv6 client ensure that it has a unique address after it configures its IPv6 address using the SLAAC allocation method?

  • It checks with the IPv6 address database that the SLAAC server hosts.
  • It contacts the DHCPv6 server via a special formed ICMPv6 message.
  • It sends an ARP message with the IPv6 address as the destination IPv6 address.
  • It sends an ICMPv6 neighbor solicitation message with the IPv6 address as the target IPv6 address.

Explanation: SLAAC is a stateless allocation method and does not use a DHCP server to manage the IPv6 addresses. When a host generates an IPv6 address, it must verify that it is unique. The host sends an ICMPv6 neighbor solicitation message with its own IPv6 address as the target. As long as no other device responds with a neighbor advertisement message, the address is unique.

14. What is used in the EUI-64 process to create an IPv6 interface ID on an IPv6-enabled interface?

  • A randomly generated 64-bit hexadecimal address
  • An IPv4 address that is configured on the interface
  • An IPv6 address that is provided by a DHCPv6 server
  • The MAC address of the IPv6 enabled interface

Explanation: The EUI-64 process uses the MAC address of an interface to construct an interface ID (IID). Because the MAC address is only 48 bits in length, 16 additional bits (FF:FE) must be added to the MAC address to create the full 64-bit IID.

15. A network administrator is implementing DHCPv6 for the company. The administrator configures a router to send RA messages with M flag as 1 by using the interface command ipv6 nd managed-config-flag. What effect will this configuration have on the operation of the clients?

  • Clients must use all configuration information that is provided by a DHCPv6 server.
  • Clients must use the information that is contained in RA messages.
  • Clients must use the prefix and prefix-length that are provided by a DHCPv6 server and generate a random interface ID.
  • Clients must use the prefix and prefix-length that are provided by RA messages and obtain additional information from a DHCPv6 server.

Explanation: Under stateful DHCPv6 configuration, which is indicated by setting M flag as 1 (through the interface command ipv6 nd managed-config-flag), the DHCPv6 server manages the dynamic IPv6 address assignments. Clients must obtain all configuration information from a DHCPv6 server.

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