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Lesson 3

Introduction toNetworking Concepts

Lesson 3

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Skills Matrix

Technology Skill Objective Domain Objective #

Configuring the DHCPServer Role

Configure Dynamic HostConfiguration Protocol(DHCP)

1.2

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Dynamic Host Configuration Protocol (DHCP)

DHCP is based heavily on BOOTP. DHCP can dynamically allocate an IP

address from a pool of addresses and

then reclaim it when it is no longerneeded. Because this process is dynamic, no

duplicate addresses are assigned by aproperly configured DHCP server, andadministrators can move computersbetween subnets without manually

configuring them.

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Dynamic Host Configuration Protocol (DHCP)

Each Microsoft Windows Server 2008edition (the Standard Edition, EnterpriseEdition, and Datacenter Edition) include

the DHCP Server service. DHCP is an optional installation. All Microsoft Windows clients

automatically install the DHCP Clientservice as part of TCP/IP, includingWindows Server 2008, Windows Server2008, Microsoft Windows Vista, and

Microsoft Windows XP.

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Dynamic Host Configuration Protocol (DHCP)

Four Key benefits to DHCP: Centralized administration of IP

configuration. Dynamic host configuration. Seamless IP host configuration. Flexibility and scalability.

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DHCP Terminology

DHCP clien t - A computer that obtains itsconfiguration information from DHCP.

DHCP server - A computer that providesDHCP configuration information to multipleclients. The IP addresses and configuration

information that the DHCP server makesavailable to the client are defined by theDHCP administrator.

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DHCP Terminology

DHCP lease - This defines the duration forwhich a DHCP server assigns an IPaddress to a DHCP client. The lease duration can be any amount of

time between 1 minute and 999 days, or itcan be unlimited.

The default lease duration is eight days.

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DHCP Messages

All DHCP messages are carried in UserDatag ram Proto co l (UDP) datagramsusing the well-known port numbers 67

(from the server) and 68 (to the client). UDP operates at the Transport Layer of

the OSI model and is a low-overhead

protocol because it does not use any typeof packet acknowledgement.

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DHCP Messages

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DHCP Lease Renewal

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DHCP Relay Agent

DHCP relies heavily on broadcast messages. Broadcast messages are generally limited to the

subnet in which they originate and are notforwarded to other subnets.

A DHCP relay agent is either a host or an IProuter that listens for DHCP (and BOOTP) clientmessages being broadcast on a subnet andthen forwards those DHCP messages to aDHCP server.

The DHCP server sends DHCP responsemessages back to the relay agent, which thenbroadcasts them onto the subnet for the DHCPclient.

Using DHCP relay agents eliminates the need to

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DHCP Relay Agent

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Automatic Private IP Addressing (APIPA)

If the DHCP client is unable to locate a DHCPserver and is not configured with an alternateconfiguration, the computer configures itself witha 169.254.0.0/255.255.0.0 address.

The auto-configured computer then tests toverify that the IP address it has chosen is notalready in use by using a gratuitous ARP

broadcast. If the chosen IP address is in use, the computer

randomly selects another address. Thecomputer makes up to 10 attempts to find anavailable IP address.

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Installing the DHCP Server Role

Adding the DHCP server role is largelywizard-driven via the Server Managerconsole and allows you to configure basic

DHCP settings at the same time that youinstall the role.

To add DHCP Server Role on a Server

Core Installation of Windows Server 2008,use the following command:

Start /w ocsetup DHCPServerCore

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Authorizing a DHCP Server

Press Ctrl+Alt+Delete on the Windows Server2008 computer. In the DHCP console, right-click DHCP and then

click Manage Authorized Servers.

In the Manage Authorized Servers dialog box,select Authorize. In the Authorize DHCP Server dialog box, key

the name or IP address of the DHCP server tobe authorized and then click OK.

The computer will list the IP and full computername and then ask for confirmation. Click OK to continue.

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DHCP Scope

Determines which IP addresses are allocated toclients.

Defines a set of IP addresses and associated

configuration information that can be supplied toa DHCP client. A scope must be defined and activated before

DHCP clients can use the DHCP server fordynamic TCP/IP configuration.

You can configure as many scopes on a DHCPserver as needed for your network environment.

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DHCP Scope

The IP addresses defined in a DHCPscope must be contiguous and areassociated with a subnet mask. If the addresses you want to assign are not

contiguous, you must create a scopeencompassing all the addresses you want

to assign and then exclude specificaddresses or address ranges from thescope.

You can create only one scope per subneton a single DHCP server.

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DHCP Scope

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Available Address Pool

Once a DHCP scope is defined andexclusion ranges are applied, theremaining addresses form what is called

an avai lab le add ress po o l within thescope.

Pooled addresses can then be

dynamically assigned to DHCP clients onthe network.

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Superscope

A DHCP superscope is an administrativegrouping of scopes that is used to supportmul t ine t s , or multiple logical subnets

(subdivisions of an IP network) on a singlenetwork segment (a portion of the IPinternetwork bounded by IP routers).

Superscopes contain only a list of memberscopes or child scopes that can beactivated together.

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DHCP Reservation

Network administrators can use DHCPreservat ions for DHCP-enabled hosts that needto have static IP addresses on your network.

Reservations must be created within a scopeand must not be excluded from the scope.

An IP address is set aside, or reserved, for aspecific network device that has the Media

Access Control (MAC) address (the hard-codedhexadecimal hardware address associated witha Network Interface Card) associated with thatIP address.

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DHCP Reservation

You can find the MAC address with theipconfig /all command.

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DHCP Reservation

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DHCP Options

DHCP options are additional client-configuration parameters that a DHCPserver can assign when serving leases to

DHCP clients. DHCP options are configured using the

DHCP console and can apply to scopes

and reservations.

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DHCP Options

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DHCP Options

DHCP options can be assigned to all scopes,one specific scope, or to a specific machinereservation.

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DHCP Options

There are four types of DHCP options inWindows Server 2008: Server op t ion s apply to all clients of the DHCP

server. Use these options for parameterscommon across all scopes on the DHCP server.

Scope op t ions apply to all clients within a scopeand are the most often used set of options.Scope options override server options.

Class o p t ions provide DHCP parameters to

DHCP clients based on type either vendorclasses or user classes. Clien t op t ions apply to individual clients. Client

options override all other options (server, scope,and class).

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Summary

Because DHCP is a key component inyour organization, you must manage andmonitor it.

DHCP management consists of backingup and restoring the database as well asreconciling, compacting, and, in somecases, removing the database.

APIPA is useful for providing addresses tosingle-segment networks that do not havea DHCP server.