Chapter 8 - DHCP

What should be done to allow PC-A to receive an IPv6 address from the DHCPv6 server?

Add the ipv6 dhcp relay command to interface Fa0/0. Client DHCPv6 messages are sent to a multicast address with link-local scope, which means that the messages will not be forwarded by routers. Because the client and server are on different subnets on different interfaces, the message will not reach the server. The router can be configured to relay the DHCPv6 messages from the client to the server by configuring the ipv6 dhcp relay command on the interface that is connected to the client.

Order the steps of configuring a router as a DHCPv4 server.

Configure a DHCP pool Exclude IP addresses

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

DHCPREQUEST

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 INFORMATION-REQUEST 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. The DHCPv6 ADVERTISE message is used by DHCPv6 servers 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.

What two methods can be used to generate an interface ID by an IPv6 host that is using SLAAC?

EUI-64 random generation

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 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.

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

It sends an ICMPv6 Neighbor Solicitation message with the IPv6 address as the target IPv6 address.

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 use the information that is contained in the RA message and contact a DHCPv6 server for additional information. 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 only use 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.

What is the result of a network technician issuing the command ip dhcp excluded-address 10.0.15.1 10.0.15.15 on a Cisco router?

The Cisco router will exclude 15 IP addresses from being leased to DHCP clients.

A network administrator is implementing the stateless DHCPv6 operation for the company. Clients are configuring IPv6 addresses as expected. However, the clients are not getting the DNS server address and the domain name information configured in the DHCP pool. What could be the cause of the problem?

The router is configured for SLAAC operation. The router is configured for SLAAC operation because there is no configuration command to change the RA M and O flag value. By default, both M and O flags are set to 0. In order to permint stateless DHCPv6 operation, the interface command ipv6 nd other-config-flag should be issued. The GigabitEthernet interface is in working condition because clients can get RA messages and configure their IPv6 addresses as expected. Also, the fact that R1 is the DHCPv6 server and clients are getting RA messages indicates that clients can communicate with the DHCP server. The number of active clients is 0 because the DHCPv6 server does not maintain the state of clients IPv6 addresses (it is not configured for stateful DHCPv6 operation). The DNS server address issue is not relevant to the problem.

A network administrator is implementing stateful DHCPv6 operation for the company. However, the clients are not using the prefix and prefix-length information that is configured in the DHCP pool. The administrator issues a show ipv6 interface command. What could be the cause of the problem?

The router is configured for stateless DHCPv6 operation. The router is configured for stateless DHCPv6 operation, which is shown by the last two lines of the show command output. Hosts will configure their IPv6 addresses by using the prefix information that is provided by RA messages. They will also obtain additional configuration information from a DHCPv6 server. The "No virtual link-local address" option and the "Duplicate Address Detection" option are irrelevant to DHCP configuration. Option "SLAAC configuration" is incorrect because by definition SLAAC will use only the information that is provided by RA messages to configure IPv6 settings.

Under which two circumstances would a router usually be configured as a DHCPv4 client?

This is an ISP requirement. The router is intended to be used as a SOHO gateway. SOHO routers are frequently required by the ISP to be configured as DHCPv4 clients in order to be connected to the provider.

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

broadcast DHCPREQUEST

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

client hardware address

n administrator issues the commands: Router(config)# interface g0/1 Router(config-if)# ip address dhcp What is the administrator trying to achieve?

configuring the router to obtain IP parameters from a DHCPv4 server The ip address dhcp command activates the DHCPv4 client on a given interface. By doing this, the router will obtain the IP parameters from a DHCPv4 server.

Which is a DHCPv4 address allocation method that assigns IPv4 addresses for a limited lease period?

dynamic allocation

Stateless DHCPv6

enabled in RA messages withthe ipv6 nd other-config-flag command enable on the client with the ipv6 address autoconfig command clients send only DHCPv6 INFORMATION-REQUEST messages to the server

Stateful DHCPv6

enabled on teh client with the ipv6 address dhcp command uses the address command to create a pool of addresses for clients the M flag is set to 1 in RA messages

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

it can provide relay services for multiple UDP services. 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

Refer to the exhibit. Based on the output that is shown, what kind of IPv6 addressing is being configured?

stateless DHCPv6 Stateful DHCPv6 pools are configured with address prefixes for hosts via the address command, whereas stateless DHCPv6 pools typically only contain information such as DNS server addresses and the domain name. RA messages that are sent from routers that are configured as stateful DHCPv6 servers have the M flag set to 1 with the command ipv6 nd managed-config-flag , whereas stateless DHCPv6 servers are indicated by setting the O flag to 1 with the ipv6 nd other-config-flag command.

An administrator wants to configure hosts to automatically assign IPv6 addresses to themselves by 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?

stateless DHCPv6 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.

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

the MAC address of the IPv6 enabled interface 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 interface ID.

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 link-local address of the router interface that is attached to the network When a PC is configured to use the SLAAC method for configuring IPv6 addresses, it will use 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.