1. Allocating IP Addressing by Using Dynamic Host Configuration Protocol

2. Overview Multimedia: The Role of DHCP in the Network Infrastructure
Adding and Authorizing the DHCP Server Service
Configuring a DHCP Scope
Configuring DHCP Reservations and Options
Configuring a DHCP Relay Agent

3. Multimedia: The Role of DHCP in the Network Infrastructure
The objective of this presentation is to provide a high-level overview of DHCP in the network infrastructure
At the end of this presentation, you will be able to:
Explain what DHCP is
Describe how DHCP works
Explain how routers can forward DHCP broadcast packets
Describe how a DHCP relay agent works

4. Lesson: Adding and Authorizing the DHCP Server Service
Why Use DHCP?
What Is Automatic Private IP Addressing?
How DHCP Allocates IP Addresses
How the DHCP Lease Generation Process Works
How the DHCP Lease Renewal Process Works
How a DHCP Server Service Is Authorized
Practice: Adding and Authorizing a DHCP Server Service

5. Why Use DHCP?
DHCP reduces the complexity and amount of administrative work by using automatic TCP/IP configuration
Manual TCP/IP Configuration
IP addresses are entered manually
IP address could be entered incorrectly
Communication and network issues can result
Frequent computer moves increase administrative effort
Automatic TCP/IP Configuration
IP addresses are supplied automatically
Correct configuration information is ensured
Client configuration is updated automatically
A common source of network problems is eliminated
Dynamic Host Configuration Protocol (DHCP) is an IP standard for
simplifying management of host IP configuration. The DHCP standard allows
you to use DHCP servers to manage dynamic allocation of IP addresses and
other IP-related configuration data for DHCP-enabled clients on your network
For example, suppose that you need to configure 100 computers with IP
configuration information. Without DHCP, you would need to manually
configure each of the 100 computers. In addition, you would have to record
what IP configuration information is on each client. If you needed to change the
IP configuration of the clients, you would have to manually reconfigure the IP
address configuration data on each computer.
Using DHCP, you would add a single DHCP server role that would support all
100 network clients. When you needed to change the IP configuration, you
would have to make the change only once on the DHCP Server service, and
then require each TCP/IP host to renew its DHCP client configuration.

6. What Is Automatic Private IP Addressing?
APIPA automatically self-configures addresses when there is no DHCP server available
Advantages
Disadvantages
Serves as a DHCP server failover mechanism for small networks
Automatically assigns an IP address in a specific range
Forces assignment of addresses typically not used
Conceals possible connectivity problems
Does not work outside x.x subnet
Is not routable
Automatic Private IP Addressing (APIPA) is a feature of Microsoft® Windows®
operating systems that automatically assigns addresses in the range
to when no DHCP server is available on the network.
How APIPA works
By default, when a Windows client starts, it is configured to broadcast DHCP
discover messages. If a DHCP server does not respond, the computer assigns
itself an APIPA x.x/16 address. APIPA ensures that the address is
unique by using Address Resolution Protocol (ARP) to generate a request on
the local network to see if any other client responds using the address it has
chosen. If there is a reply, APIPA tries another random address and repeats the
test. The computer will then send out a discover message every three minutes in
an attempt to communicate with a DHCP server. Once communication is
reestablished with the DHCP server, the client uses the addressing assigned by
the DHCP server.
After the network adapter is assigned an IP address, the computer can
communicate with any other computer that is connected to the same local area
network (LAN) and that is also configured through APIPA or has the IP address
manually set to the x.x address range.

7. How DHCP Allocates IP Addresses
DHCP Client2: IP configuration from DHCP server
Non-DHCP Client: Static IP configuration
Lease Renewal
Lease Generation
DHCP Server
A lease is the length of time for which a DHCP client can use a dynamically
assigned IP address configuration. Before the lease time expires, the client must
either renew the lease or obtain a new lease from DHCP.
DHCP
Database
DHCP Client1: IP configuration from DHCP server
IP Address1: Leased to DHCP Client1
IP Address2: Leased to DHCP Client2
IP Address3: Available to be leased

8. How the DHCP Lease Generation Process Works
DHCP client broadcasts a DHCPDISCOVER packet 1
DHCP servers broadcast a DHCPOFFER packet 2
DHCP client broadcasts a DHCPREQUEST packet 3
DHCP Server1 broadcasts a DHCPACK packet 4
DHCP Client
DHCP Server1
DHCP Server2
DHCP Server2
DHCP Server1
DHCP Client
The DHCP lease generation process is the process by which the DHCP client
receives IP addressing configuration data from the DHCP server.
DHCP discover
The DHCP client broadcasts a DHCPDISCOVER packet to locate a DHCP
server. A DHCPDISCOVER packet is a message that DHCP clients send the
first time that they attempt to log on to the network and request IP address
information from a DHCP server.
DHCP offer
The DHCP server broadcasts a DHCPOFFER packet to the client. A
DHCPOFFER packet is a message that DHCP servers use to offer the lease of
an IP address to a DHCP client when it starts on the network.
Each responding DHCP server reserves the offered IP address so that the
address will not be offered to another DHCP client before the requesting
Client’s acceptance.
If the client does not receive an offer after four requests, the client uses APIPA
to configure itself. When a DHCP server becomes available, clients receive
valid IP addresses, allowing those clients to communicate with hosts both on
and off their subnet.
DHCP request
The DHCP client broadcasts a DHCPREQUEST packet. A DHCPREQUEST
packet is a message that a client sends to the DHCP server to request or renew
the lease of the client’s IP address.
The DHCP client responds to the first DHCPOFFER packet that it receives by
broadcasting a DHCPREQUEST packet to accept the offer. The
DHCPREQUEST packet includes the identification of the server whose offer
the client accepted. All other DHCP servers then retract their offers and retain
their IP addresses for other IP lease requests.
DHCP acknowledgement or DHCP negative acknowledgement
The DHCP server broadcasts a DHCPACK packet to the client. A DHCPACK
packet is a message that the DHCP server sends to a client to acknowledge and
complete a client.s request for leased configuration. This message contains a
valid IP address lease and other IP configuration data.
When the DHCP client receives the acknowledgment, TCP/IP initializes by
using the IP configuration data that the DHCP server provides. The client also
binds the TCP/IP protocol to the network services and network adapter,
permitting the client to communicate on the network.
The DHCP server sends a DHCP negative acknowledgement (DHCPNAK
packet) if the IP address that was offered is no longer valid or is now in use by
another computer. The client must then restart the lease process.
DHCP client broadcasts a DHCPDISCOVER packet 1
DHCP servers broadcast a DHCPOFFER packet 2
DHCP client broadcasts a DHCPREQUEST packet 3
DHCP Server1 broadcasts a DHCPACK packet 4

9. How the DHCP Lease Renewal Process Works
DHCP Client
DHCP Server1
DHCP Server2
DHCP client sends a DHCPREQUEST packet 1
DHCP Server1 sends a DHCPACK packet 2
50% of lease duration has expired
DHCP Client
DHCP Server1
DHCP Server2
100% of lease duration has expired
87.5% of lease duration has expired
50% of lease duration has expired
The client must renew its IP configuration data before the lease period expires.
A DHCP client automatically attempts to renew its lease as soon as 50 percent
of the lease duration has expired. The DHCP client also attempts to renew its IP
address lease each time that the computer restarts. To attempt a lease renewal,
the DHCP client sends a DHCPREQUEST packet directly to the DHCP server
from which the client obtained the lease.
If the DHCP server is available, it renews the lease and sends the client a
DHCPACK packet that includes the new lease duration and any updated
configuration parameters. The client updates its configuration when it receives
the acknowledgment. If the DHCP server is unavailable, the client continues to
use its current configuration parameters.
If the DHCP client fails to renew its lease the first time, the DHCP client
broadcasts a DHCPDISCOVER packet to update its address lease when 87.5
percent of the current lease duration expires. At this stage, the DHCP client
accepts a lease that any DHCP server has issued.
If the client fails to renew it’s lease, after 87.5% of the lease has expired, then the DHCP lease generation process starts over again with a DHCP client broadcasting a DHCPDISCOVER
If the client fails to renew its lease, after 50% of the lease duration has expired, then the DHCP lease renewal process will begin again after 87.5% of the lease duration has expired
DHCP Client sends a DHCPREQUEST packet 1
DHCP Server1 sends a DHCPACK packet 2

10. How a DHCP Server Service Is Authorized
If DHCP Server1 finds its IP address on the list, the service starts and supports DHCP clients
DHCP Server1 checks with the domain controller to obtain a list of authorized DHCP servers
Domain
Controller
Active
Directory
DHCP Client
DHCP Server1
Authorized
Services DHCP requests
DHCP Server2
Unauthorized
Does not service DHCP requests
DHCP authorization is the process of registering the DHCP Server service in
an Active Directory® directory service domain to support DHCP clients. DHCP
authorization is only for DHCP servers running Windows Server 2003 and
Windows 2000 in an Active Directory domain
Authorizing a DHCP allows you to control the addition of DHCP servers to the
domain
DHCP client receives IP address
from authorized DHCP Server1
DHCP Server2 checks with the
domain controller to obtain a list of
authorized DHCP servers
If DHCP Server2 does not find its IP address on the list, the service does not start and support DHCP clients
DHCP authorization is the process of registering the DHCP Server service in the Active Directory domain to support DHCP clients

11. Practice: Adding and Authorizing a DHCP Server Service
In this practice, you will:
Add a DHCP server
Authorize the DHCP Server service

12. Lesson: Configuring a DHCP Scope
What Are DHCP Scopes?
Demonstration: Configuring a DHCP Scope
What Are Superscopes and Multicast Scopes?
What Is Network Monitor?
Practice: Configuring a DHCP Scope

13. A scope is a range of IP addresses that are available to be leased
What Are DHCP Scopes?
A scope is a range of IP addresses that are available to be leased
DHCP Server
LAN A
LAN B
Scope A
Scope B
Scope Properties
Network ID
Subnet mask
Lease duration
Network IP address range
Scope name
Exclusion range

14. Configuring a DHCP Scope

15. Practice: Configuring a DHCP Scope
In this practice, you will:
Configure two DHCP scopes
Configure a DHCP superscope
Verify IP address allocation by using Network Monitor

16. Lesson: Configuring DHCP Reservations and Options
What Is a DHCP Reservation?
What Are DHCP Options?
Demonstration: Configuring DHCP Reservations and Options
How DHCP-Server, Scope, and Reserved-Client Options Are Applied
How DHCP Class-Level Options Are Applied
Practice: Configuring DHCP Reservations Options

17. What Is a DHCP Reservation?
A reservation is a specific IP address, within a scope, that is permanently reserved for lease to a specific DHCP client
Subnet A
Subnet B
Workstation 1
DHCP Server
Workstation 2
File and Print Server
IP Address1: Leased to Workstation 1
IP Address2: Leased to Workstation 2
IP Address3: Reserved for File and Print Server
You can use reservations for DHCP-enabled devices that need to have the same
IP address on your network, such as file and print servers or other application
servers.
Some organizations use IP addresses to identify specific clients. For example,
an organization may want to limit which clients can access the Internet through
a firewall. To ensure that specific clients always get the same IP address, these
organizations can use DHCP reservations for all clients.

18. What Is a DHCP Reservation?
You can use reservations for DHCP-enabled devices that need to have the same
IP address on your network, such as file and print servers or other application
servers.
Some organizations use IP addresses to identify specific clients. For example,
an organization may want to limit which clients can access the Internet through
a firewall. To ensure that specific clients always get the same IP address, these
organizations can use DHCP reservations for all clients.

19. What Are DHCP Options?
DHCP options are configuration parameters that a DHCP server assigns to clients
DHCP Client
DHCP Client IP Configuration Data
Client’s IP address
Client’s subnet mask
DHCP options
Why use DHCP options
A DHCP option allows increased functionality on the network. The lease
generation process provides the DHCP client with an IP address and a subnet
mask. DHCP options allow you to configure additional IP configuration data
for your DHCP clients.
DHCP Server

20. What Are DHCP Options?

21. Demonstration: Configuring DHCP Reservations and Options
Your instructor will demonstrate how to:
Configure a DHCP reservation
Configure a DHCP server option
Configure a DHCP scope option

22. Practice: Configuring DHCP Options
In this practice, you will:
Configure and test a DHCP reservation
Configure DHCP server and scope options
Configure and test a new DHCP user class