DHCP allows client devices to automatically receive IP addresses and network configuration from a server. It uses UDP and broadcasts packets to lease IP addresses. The DHCP server can assign addresses from scopes that define ranges. Addresses are leased for a duration, and clients renew leases before they expire to maintain connectivity. A relay agent can extend DHCP to devices across routers.

1. DHCP

2. Overview of DHCP
• DHCP
• DHCP IP Leasing Process
• Renewing an IP Address
• Installing the DHCP Service
• DHCP Relay Agent
• Superscope Implementation
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3. Dynamic Host Configuration Protocol
(DHCP)
DHCP is a protocol that allows client computers to automatically
receive an IP address and TCP/IP settings from a Server.
Allows servers to assign or lease IP addresses to computers and other
devices that are enabled as DHCP clients on the network.
All DHCP messages are carried in User Datagram Protocol (UDP)
datagrams using the well-known port numbers 67 (from the server)
and 68 (to the client).
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4. 4
DHCP PORTS
DHCP(Port-67):
Bootstrap Protocol (BOOTP) Server;
DHCP(Port-68):
Bootstrap Protocol (BOOTP) Client;
The ipconfig /all command will indicate whether the configuration
came from a DHCP server computer

5. 5
DHCP Settings in Client Side

6. 6
DHCP Details in cmd

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Leasing an IP Address
• An IP address is leased during the boot process
• The overall process is composed of four broadcast
packets:
• It will call DORA Process:
• DHCPDISCOVER
• DHCPOFFER
• DHCPREQUEST
• DHCPACK

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Leasing an IP Address
• 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

9. 9
Four Packets In The DHCP IP
Leasing Process

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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. If the renewal
process fails, it attempts again after 87.5% of the
lease time has expired.
• Renewing the lease involves the client sending a
DHCP Request packet to DHCP Server

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Renewing an IP Address

12. More on the Renewal Process…
• DHCP Client, at startup, attempts to reach the DHCP
Server
Server Available:
• If the server is available and the lease has not yet
expired, the client retains the IP address
• If the server is available and the lease has expired,
the client attempts to renew the lease.
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13. More on the Renewal Process…
• DHCP Client, at startup, attempts to reach the DHCP
Server
Server Unavailable:
• If the server is unavailable, the client will ping the
previously assigned default gateway to determine
if it’s on the same network.
• If the gateway responds and the lease hasn’t expired, the
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client retains the IP address
• If the gateway doesn’t respond the client will send a
DISCOVER packet to begin the lease process over

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Question?
• When a DHCP Server does not respond to a Client’s call for an
IP Address, the client will autoconfigure itself APIPA IP.
• The client selects an IP address from the 169.254.0.0
subnet
• The client will attempt to contact a DHCP server using
DISCOVER packets every 5 minutes
• The lease duration can be any amount of time between 1
minute and 999 days, or it can be unlimited.
• The default lease duration is eight days.

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Installing the DHCP Service
• When placing a DHCP Service on a Server in a Domain:
• Install the DHCP Server Service
• Authorize DHCP Server in Active Directory
• Configure DHCP Server with appropriate scopes,
exclusions, reservations and options
• Activate the DHCP Server’s Scopes
• When placing a DHCP Service on a Server in a Workgroup:
• Install the DHCP Server Service
• Configure DHCP Server with appropriate scopes,
exclusions, reservations and options
• Activate the DHCP Server’s Scopes

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Authorizing the DHCP Service
• A server that is a member of a domain can be authorized
• During the installation of the service: the Install Wizard
provides an option to authorize the server
• Only members of the Enterprise Admins(win2003,win2008)
group can authorize a server
• A server that is a member of a workgroup(win7,xp)does not need
to be authorized.

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Configuring DHCP Scopes
• Scope defines a range of IP addresses
• Each scope is configured with:
• Description- Name of Scope
• Starting IP address- 192.168.1.51
• Ending IP address- 192.168.1.200
• Subnet mask- 255.255.255.0
• Exclusions
• Lease duration- 8Day
Reserve a range of addresses at beginning or end of range that
can be used for static addresses

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Configuring DHCP Scopes
• Lease duration defines how long client computers are
allowed to use an IP address
• Default lease duration varies based on the network
type and the DHCP Server version
• A scope must be activated before the DHCP service
can begin using it

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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
• Reservations are created based on MAC addresses

20. Creating DHCP Exclusions
• Exclusions are IP Addresses that are within the
subnet defined within the scope but that should not be
assigned to a dhcp client
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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

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DHCP Relay Agent
• DHCP packets cannot travel across a router
• A relay agent is necessary in order to have a single DHCP
server handle all leases on both network segments
• This can be a Windows 2003/2008 server with DHCP
Relay Agent protocol installed or a router that is configured
as a relay
• Relay agents receive broadcast DHCP packets and forward
them as unicast packets to a DHCP server
• The relay agent must be configured with the IP address of the
DHCP server
• The DHCP relay cannot be installed on the same server as the
DHCP service

23. 23
Configuring a DHCP Relay

24. DHCP Relay Agent
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25. UNICASTING AND BROADCASTING
Unicast Message:
• When using unicast method, one device will send the message to
exactly one destination device. If some device needs to send a
message to multiple devices, it will have to send multiple
unicast messages, each message addressed to a specific device.
So, the sender has to send a separate message to each destination
device.
Broadcast Message:
• The second method of sending messages is called the
broadcasting. Broadcast is a packet that's sent to all devices on
specific network. The destination address in the packet is the
special broadcast address. If the packet has a broadcast address,
all devices that receive that message will process it
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Superscopes
• Used to combine multiple scopes into a single logical
scope
• Allows multiple scopes to be treated as a single scope
• Useful when a single physical network segment
contains more than one logical subnet
• If a superscope is used, then the DHCP server offers
only one lease as opposed to multiple leases

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Example 1: No Super scope
• One physical network
segment
• One logical subnet
(192.168.1)
• One DHCP Server
• Single scope is used to
service all DHCP
clients on Subnet A

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Example 2: Superscope
• One physical network segment
• Multiple logical subnets
• 192.168.1
• 192.168.2
• 192.168.3
• Three single scopes created and
joined into one superscope
• One DHCP Server services all
clients on Subnet A with an IP
address from the superscope
• Router configured with multiple
addresses to allow packets to
move from one logical network
to another

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Example 3: Superscope
Implemented across a Router
• Two physical network
segments: Subnet A and
Subnet B
• One DHCP Server
• Router configured with
Relay Agent
• Something that will pass
Discover Packets back
and forth from DHCP
Clients and DHCP Server

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Superscope Implemented across a Router
• Subnet A:
• One physical segment
• One logical subnet (192.168.1)
• One single scope defined
• DHCP server distributes
addresses to clients on Subnet
A using addresses in single
scope
• Subnet B:
• One physical segment
• Two logical subnets (192.168.2
& 192.168.3)
• Two single scopes defined and
joined into one Superscope
• DHCP server distributes
address to clients on Subnet B
using addresses in superscope

31. Saving and Restoring DHCP
Configuration
• DHCP Server configurations can be saved to a file
• These saved settings can then be used to restore the server to a
known state OR to use the same settings on another server
• To save the configuration :
• To restore the configuration:
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32. Advantages & Disadvantages
Advantages:
• To implement DHCP requires no additional costs.
• Duplicated IP addresses are prevented
• Reduces the amount of time you spend configuring computers on
your network
• DHCP servers only allocate IP addresses to clients when they
request them.
Disadvantages:
• The DHCP server can be a single point of failure in networking
environments that only have one DHCP server.
• Place a DHCP relay agent on each segment
• Configure routers to forward Bootstrap Protocol (BootP)
broadcasts.
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Conflict Detection
• Using DHCP does not prevent static IP configuration
• A DHCP server may hand out an IP address that was
already statically assigned
• Conflict detection prevents a DHCP server from
creating IP address conflicts
• A DHCP server pings an IP address before it is leased
to a client computer