DHCP Dynamic Host Configuration Protocol

1

ObjectivesDescribe the DHCP lease and renewal

processUnderstand and describe the purpose of a

DHCP relayInstall DHCPConfigure DHCP scopes, superscopes,

reservations, vendor classes, and user classesManage and monitor DHCPTroubleshoot DHCPInstall and configure a DHCP relay

2

The DHCP ProcessUsed to automatically deliver IP addressing

information to client computers on a network

Can also deliver IP address information to servers and other devices such as printers

Use of DHCP reduces time spent configuring computers on network

Client computers use DHCP by default unless static IP address is specified during installation

3

Windows XP TCP/IP Properties

4

Leasing an IP AddressProcess to lease an address is composed of four packetsDHCPDISCOVER: sent from the client

computer to the broadcast IP address 255.255.255.255

DHCPOFFER: response sent after receiving DHCPDISCOVER packet

DHCPREQUEST: response of DHCP client after receiving DHCPOFFER packet

DHCPACK: response sent by chosen DHCP server indicating confirmation that lease has been chosen and client can now use the lease

5

The Four Packets in the DHCP Lease Process

6

Renewing an IP AddressAn IP address leased using DHCP can be either permanent or timed

Permanent addressDHCP server never reuses the address for

another clientTimed lease

Allows clients to use an IP address for a specified period of time

Windows clients attempt to renew their lease after 50% of lease time has expired

ipconfig /release command is used to force the release of a DHCP address

7

The DHCP Lease Renewal Process

8

DHCP RelayDHCP packetsAre broadcast packets during the leasing

processCannot travel across a router

DHCP relayReceives broadcast DHCP packets from clients

and forwards them as unicast packets to a DHCP server

Must be configured with IP address of the DHCP server to deliver unicast packets

DHCP Relay Service cannot be installed on the same server as the DHCP Service

9

Installing DHCP

10

AuthorizationControl over DHCP is very importantAn unauthorized DHCP server can quickly

hand out incorrect IP addressing information to hundreds of client computers

To exercise control over DHCPWindows Server 2003 must be authorized

to start DHCP Service Authorization of a DHCP server takes place

in Active Directory

11

Authorization (Continued)

To authorize DHCP serverMust be a member of Enterprise Admins

group orMember of Enterprise Admins group must

delegate permissions to you

12

Unauthorized DHCP server error in Event Viewer

13

The DHCP Management Snap-In

14

Authorized DHCP server information in Event Viewer

15

Configuring DHCPNormally accomplished with the DHCP

management snap-inNETSH

Command used to configure DHCPUsed in larger organizations where there is

a need to make changes programmatically using batch files

16

Configuring DHCP (Continued)DHCP elements that can be configured

includeScopesSuperscopesMulticast scopesReservationsVendor and user classesScope, server, and reservation options

17

ScopesUsed to define a range of IP addresses for the DHCP server to hand out to client computers

Each scope is configured withNameDescriptionStarting IP addressEnding IP addressSubnet maskExclusionsLease duration

18

Scopes (Continued)Name and description

Appears in the DHCP management snap-inStarting and ending IP addresses

Define range of IP addresses that can be handed out by the DHCP server

Strategies when defining starting and ending IP addressesConfigure scope to use all available

addresses on a subnet, then exclude the static IP addresses being used by hosts

Configure scope to use addresses that are not already in use

19

Scopes (Continued)Exclusions

Used to prevent some IP addresses in a scope from being handed out dynamically

Lease durationDefines how long client computers are

allowed to use an IP addressDefault lease duration used by Windows

Server 2003 is eight daysDHCP server

Does not begin using a scope immediately after creation

Scope must be activated before DHCP Service can begin using the scope

20

Scope Settings

21

Superscopes

Used to combine multiple scopes into a single logical scope

Used when a single physical part of the network has two subnets

22

A Superscope Containing Two Scopes

23

Multicast ScopesUsed to deliver multicast addresses to

applications that require itTime To Live (TTL)

Defines the number of routers through which a multicast packet can move

ExclusionsDefine addresses between the start and

end IP addresses that are not handed outLease duration

The length of time that an application can use a multicast address

Default lease length is 30 days

24

ReservationsUsed to hand out a specific IP address to a particular client computer or device on the network

Can also be beneficial when firewalls are in place

Created based on the MAC address of the network card

25

Creating a Reservation

26

Configuring OptionsDHCP can hand out the following IP

configuration optionsDefault gatewayDNS serverWINS server

DNS is often configured at the server level

27

SummaryDHCP

Dynamically assigns IP addressesCan assign multicast IP addresses

DHCP lease processComposed of DHCPDISCOVER,

DHCPOFFER, DHCPREQUEST, and DHCPACK

DHCPNAK: used by DHCP servers to decline renewal of lease

DHCPRELEASE: used by clients to inform DHCP server that lease is no longer required

28

Summary (Continued)

Renewing leaseClients attempt to renew at 50%, 87.5%,

and 100% of lease timeCommands ipconfig /release and

ipconfig /renewCan release and renew DHCP leases

DHCP serverMust be authorized in Active Directory to

lease addressesMust be member of Enterprise Admins to

authorize DHCP

29

Summary (Continued)Scope

Defines range of IP addresses that are leased to clients

Must be activated before DHCP server leases addresses in the scope

SuperscopeCombines two scopes into single scope

Exclusion in scopeUsed to stop a DHCP server from handing

out specific addresses or range of addresses within a scope

30