Dynamic Host Configuration

Protocol

BY kinish kumarwww.kinishcybersec.blogspot.inhttps://www.facebook.com/kinishkumar

Objectives

• Outline the benefits of using DHCP• Describe the DHCP lease and renewal process• Install and authorize the DHCP service• Configure DHCP scopes• Create DHCP reservations for client computers• Configure DHCP options• Understand and describe the purpose of a DHCP

relay• Install and configure a DHCP relay

DHCP Overview

• Used to automatically deliver IP addressing • Reduces the amount of time you spend configuring

computers on your network• Used by default unless you specify otherwise• The ipconfig /all command will indicate whether

the configuration came from a DHCP server computer

DHCP Overview (continued)

TCP/IP Properties

DHCP Overview (continued)

The ipconfig /all command

Leasing an IP Address

• An IP address is leased during the boot process• The overall process is composed of four broadcast

packets:– DHCPDISCOVER

– DHCPOFFER

– DHCPREQUEST

– DHCPACK

Leasing an IP Address (continued)

• Any DHCP server that receives the DHCPDISCOVER packet responds with a DHCPOFFER packet

• The DHCP client responds to the DHCPOFFER packet it receives with a DHCPREQUEST packet

• A DHCPACK packet indicates confirmation that the client can use the lease

• Once DHCPACK is received, the client can start using the IP address and options in the lease

Leasing an IP Address (continued)

The four packets in the DHCP lease process

Renewing an IP Address

• The IP address can either be permanent or timed• A permanent address is never reused for another

client• Timed leases expire after a certain amount of time• Windows clients attempt to renew their lease after

50% of the lease time has expired• A DHCP server may either honor or reject a renew

request

Renewing an IP Address (continued)

The DHCP lease renewable process

Installing and Authorizing the DHCP Service

• A DHCP service must be authorized after installation

Installing the DHCP Service

• DHCP is a standard service • It is included in Windows Server 2003• It is not installed as part of a default installation

Installing the DHCP Service (continued)

Installing DHCP

Installing DHCP

• Objective: Install DHCP on Windows Server 2003• Make sure your network connection is statically

configured• Install the service using the Add/Remove Windows

Components utility

Authorizing the DHCP Service

• Unauthorized DHCP servers can hand out bad information

• DHCP will not start unless authorized• If Active Directory is used, authorization takes place

in Active Directory• DHCP servers are automatically authorized under

certain conditions

Authorizing the DHCP Service (continued)

Unauthorized DHCP server error in Event Viewer

The DHCP management snap-in

Authorizing the DHCP Service (continued)

Authorized DHCP server information in Event Viewer

Starting an Authorized DHCP Server

• Objective: View the results of starting a DHCP server that does not participate in an Active Directory domain

• Check to make sure the service is running• Check out any relevant events using the System Log

Installing the Active Directory Service

• Objective: Install the Active Directory service on your computer and participate in an Active Directory domain

• Use the dcpromo utility• Select “domain controller for a new domain”• Select “domain in a new forest”• Continue through the resulting dialogs

Starting an Unauthorized DHCP Server

• Objective: View the results of starting an unauthorized DHCP server

• View the System Log to see the result of starting an unauthorized DHCP server

Authorizing a DHCP Server

• Objective: Authorize a DHCP server in Active Directory

• Go to the DHCP snap-in and choose the activate option

Configuring DHCP Scopes

• Scope defines a range of IP addresses • Each scope is configured with:

– Description– Starting IP address– Ending IP address– Subnet mask– Exclusions– Lease duration

• Two strategies exist for defining the starting and ending IP addresses– Allow all and exempt the few static addresses– Use only the addresses not already in use

Configuring DHCP Scopes (continued)

Scope Settings

Configuring DHCP Scopes (continued)

• Exclusions are used to prevent some IP addresses from being handed out dynamically

• Lease duration defines how long client computers are allowed to use an IP address

• Default lease duration is eight days• A scope must be activated before the DHCP service

can begin using it

Creating a Scope

• Objective: Create a scope to distribute IP addresses to client computers

• Manually enter the IP configuration settings as directed by the text

• Create a new scope using the configuration settings provided

Activating and Testing a Scope

• Objective: Activate a DHCP scope, and then test it with a partner

• One person will activate the scope created in the previous activity

• Another person will try to obtain an automatic IP address from the server

Superscopes

• Used to combine multiple scopes into a single logical scope

• Allows multiple scopes to be treated as a single scope

• If a superscope is used, then the DHCP server offers only one lease as opposed to multiple leases

Superscopes (continued)

A superscope containing two scopes

Configuring a Superscope

• Objective: Combine two scopes into a single logical unit using a superscope

• First, create a second scope in addition to the scope already created in a previous activity

• Create a superscope to encompass the two scopes• Use the DHCP snap-in for this activity

Deleting a Superscope

• Objective: Delete a superscope, leaving each scope independent

• Make sure you delete the superscope without deleting the subscopes

Multicast Scopes

• Used to deliver multicast addresses to applications that require it

• Multicast addresses are used to deliver packets to groups of computers

• Start and end IP addresses define the range of addresses that can be handed out by DHCP servers

• TTL defines the number of routers through which a multicast packet can move

Multicast Scopes (continued)

• Exclusions define addresses that should not be handed out

• Lease duration defines the length of time that an application can use a multicast address

• Default lease length is 30 days

Creating a Multicast Scope

• Objective: Create a multicast scope to deliver multicast addresses to applications

• Setting up a multicast scope is very similar to setting up any other scope

• Set the scope configuration to that specified in the text

Deleting a Multicast Scope

• Objective: Delete a multicast scope• Right click on the scope and issue the delete

command

Creating DHCP Reservations

• Reservations are used to hand out a specific IP address to a particular client

• Useful when delivering IP addresses to devices that would normally use static addresses

• Can also be beneficial when firewalls are in place• Reservations are created based on MAC addresses

Creating DHCP Reservations (continued)

Creating Reservation

Creating and Testing a Reservation

• Objective: Create a DHCP reservation, and test it with a client

• Configure the server to reserve an IP address for a client machine

• Test to see if the client machine picks up the reserved address

Configuring DHCP Options

• DHCP can hand out a variety of other IP configuration options

• It is common that all workstations within an entire organization use the same DNS servers

• DNS is often configured at the server level

Configuring DHCP Options (continued)

Server setting options

Configuring DHCP Options (continued)

Settings Scope Options

Setting Server Options

• Objective: Set the DNS server option for a DHCP server

• Check 006 DNS servers option• Add the IP address x.0.0.250

Setting Scope Options

• Objective: Set the default gateway in the scope options

• Use the DHCP snap-in to complete this activity

Testing Server & Scope Options

• Objective: Activate a DHCP scope, and then test it with a partner to ensure that scope options are handed out

• Activate a DHCP scope• Configure a client to access the server• Check the default gateway and DNS settings to find

out whether or not the configurations entered in previous activities were done correctly

Vendor and User Classes

• Used to differentiate between clients within a scope • Vendor classes are based on the operating system• User classes are defined based on network

connectivity or the administrator• You can use the ipconfig /setclassid command to set

the DHCP user class ID

Vendor and User Classes (continued)

Vendor Classes

Setting a class ID

Vendor and User Classes (continued)

User classes

Configuring a DHCP Relay

• DHCP packets cannot travel across a router• A relay agent is necessary in order to have a

single DHCP server handle all leases• Relay agents receive broadcast DHCP packets

and forward them as unicast packets to a DHCP server

• The DHCP relay cannot be installed on the same server as the DHCP service

Configuring a DHCP Relay (continued)

Using DHCP relay agents on a routed network

Configuring a DHCP Relay (continued)

The Routing and Remote Access tool

Configuring a DHCP Relay

• Objective: Uninstall the DHCP service from your computer and configure it as a DHCP relay

• Uninstall the DHCP service• Configure the computer as a relay by using the

Routing and Remote Access tool provided in Windows

Summary

• DHCP dynamically assigns IP address information to clients on a network

• The DHCP lease process is composed of four packets: – DHCPDISCOVER– DHCPOFFER– DHCPREQUEST– DHCPACK

• A DHCP client attempts to renew its lease at 50%, 87.5%, and 100% of the lease time

• The commands ipconfig /release and ipconfig /renew can be used to release and renew DHCP leases

Summary (continued)

• If the Active Directory service is present on your network, each DHCP server must be authorized in Active Directory to lease addresses to clients

• A scope defines a range of IP addresses that are leased to clients

• A superscope combines two scopes into a single logical unit to service network segments with two subnets

Summary (continued)

• An exclusion in a scope can stop a DHCP server from handing out specific addresses

• A reservation allows you to give a specific workstation a defined IP address by tying the DHCP lease to the MAC address of the client

• Vendor and user classes can be used to configure some client computers with different options, depending on the class to which they belong

• A DHCP relay agent is required on each network that requires IP configuration from a DHCP server across a router