Lesson 6: Dynamic Host Configuration Protocol A

 DHCP allows you to assign IP addresses,
subnet masks, and other configuration
information to client computers on a local
network.
 When a DHCP server is available, computers
that are configured to obtain an IP
addresses automatically request and
receive their IP configuration from that
DHCP server upon booting.

 Dynamic Host Configuration Protocol
 Automatic configuration
▪ IP address
▪ Subnet mask
▪ Other Information
 Requires DHCP Server
 Windows Server 2008 Role

 Configuration of large and even midsize networks is much
simpler.
 Once you enter the IP configuration information in one
place(the server) it’s automatically propagated to clients,
eliminating the risk that a user will misconfigure some
parameters and require you to fix them.
 IP addresses are conserved because DHCP assigns them only
when requested.
 IP configuration becomes almost completely automatic.
 Allows a preboot execution environment (PXE) client to get a
TCP/IP address from DHCP.
 PXE clients (also called Microsoft Remote Installation Services (RIS)
clients) can get an IP address without needing to have an operating
system installed. This allows RIS clients to connect to a RIS server
through the TCP/IP protocol and download an operating system
remotely.

 DHCP can become a single point of failure for your
network.
 If the DHCP server contains incorrect information,
the misinformation will automatically be delivered
to all your DHCP clients.
 To fix the problem, you might have to visit each machine
and reconfigure it.
 If you want to use DHCP on a multisegment
network,
 you must put either a DHCP server or a rely agent on
each segment,
 or you must ensure that your router can forward
Bootstrap Protocol (BOOTP) broadcasts.a

 Configure dynamic host configuration
protocol (DHCP).

1. Installing DHCP server.
2. Configuring a DHCP server.

 After this lesson you will be able to:
 Deploy a DHCP server.
 Configure a server DHCP scope.
 Configure DHCP scope options.

 The negotiation between a DHCP client
and DHCP server occurs in four stages:
1. Broadcast DHCP Discover.
2. Respond with DHCP Offer.
3. Respond with DHCP Request.
4. Confirm with DHCP Ask.

1. Broadcast DHCPISCOVER
2. Respond with DHCPOFFER
3. Respond with DHCPREQUEST
4. Confirm with DHCPACK

 Every DHCP server maintains a database of
addresses that the server can distribute to
clients.
 When a DHCP server assign a computer an
address, it assigns that address in the form
of a lease that lasts six or eight days by
default.
 The DHCP server keeps tracks of leased
addresses so that no address is assigned to
two clients.

 To prevent an IP address from being indefinitely
assigned to a client that has disconnected from the
network , DHCP server reclaim addresses at the end
of the DHCP lease period.
 If the DHCP server is online
▪ Accept the renewal
 If the DHCP server is not available
▪ DHCP Client tries to renew the DHCP lease again after half the
remaining lease period
 If the DHCP server is not available after 87.5% of lease
time has elapsed
▪ DHCP client attempts to locate a new DHCP server

 If the DHCP client shuts down normally, or if an
administrator runs the command ipconfig/release
 The client sends a DHCP release message to the DHCP
server.
 The DHCP server marks the IP address as available and
can reassign it to a different DHCP client.

 If the DHCP client disconnects suddenly from the
network (does not have the opportunity to send a
DHCP release message).
 The DHCP server will not assign the IP address to a
different client until the DHCP lease expires.

 ipconfig /renew
 Instructs the DHCP client to request a lease renewal.
▪ If the client already has a lease, it requests a renewal from
the server that issued the current lease.
▪ if the client doesn’t currently have a lease, It initiates the
DHCP mating dance, listens for lease offers, and chooses
one it likes.
 ipconfig /release
 Forces the client to immediately give up its lease by
sending the server a DHCP release notification.
 ipconfig /setclassid classID
 Sets a new class ID for the client.

 Scope:
 A range of IP addresses must be defined at the
DHCP server.
 Defines a single physical subnet on the network to
which DHCP services are offered.
 Example:
▪ If you have two subnets
▪ 10.0.1.0/24 and 192.168.10.0/24
▪ DHCP server:
▪ directly connect to each subnet
▪ define a scope for each subnets & associated address ranges

 Superscope
 Enables the DHCP server to provide addresses from
more than one scope to clients on the same physical
subnet.
 Helpful when clients within the same subnet have
more than one IP network and thus need IPs from
more than one address pool.
 Microsoft’s DHCP snap-in allows you to manage IP
address assignment in the superscope, though you
must still configure other scope options individually
for each child scope.

 Exclusions and Reservations
 Exclusions are IP addresses within the range that you never
want automatically assigned.
 Reservations are IP addresses within the range for which
you want a permanent DHCP lease. They essentially reserve a
particular IP address for a particular device.
 Address Pool
 The range of IP addresses that the DHCP server can assign is
called its address pool
 DHCP Relay Agent
 If no DHCP server is available on the client’s network, you can
use a DHCP relay agent to forward DHCP broadcasts from the
client’s network to the DHCP server.

 You should understand what a superscope
is for the 70-642 exam.

 DHCP options provide clients with
additional configuration parameters
 Such as DNS or WINS server address.
 More than 60 standard DHCP options are
available

 The most common DHCP Options, For an IPv4 configuration are:
 003 Router:
▪ Used to provide a list of available routers or default gateways on the same subnet
 006 DNS Servers:
▪ Used to provide a list of DNS servers
 015 DNS Domain Name:
▪ Used to provide the DNS suffix
▪ Allows clients to perform dynamic DNS updates.
 044 WINS/ NBNS Servers:
▪ Used to configure the IP addresses of WINS servers.
 046 WINS/ NBT Node type:
▪ Used to configure the preferred NetBIOS name resolution method. There are four settings for node
type:
▪ B node (0x1): Broadcast for NetBIOS resolution
▪ P node (0x2): Peer-to-peer (WINS) server for NetBIOS resolution
▪ M node (0x4): Mixed node (does a B node and then a P node)
▪ H node (0x8): Hybrid node (does a P node and then a B node)
 051 Lease:
▪ Used to configure a special lease duration
▪ Assigns a special lease duration only to remote access clients.
▪ This option relies on user class information advertised by this client type.

 You need to understand these six DHCP
options for the 70-642 exam.

 To install and configure a DHCP server on a
computer running windows server 2008
 Deploy a server on the physical subnet for which
you want to provide addressing.
 Be sure to assign the server a static IP address
that will be compatible with the address range
planned for the local subnet.
 Use the add roles wizard to add the DHCP server
role on the computer.

Lesson 6: Dynamic Host Configuration Protocol A

 The wizard presents you with the
following configuration pages:
1. Select network connection bindings.
2. Specify IPv4 DNS Server settings.
3. Specify IPv4 WINS Server settings.
4. Add or edit DHCP scopes.
5. Configure DHCPv6 Stateless mode.
6. Specify IPv6 DNS Server settings.
7. Authorize DHCP Server.

 You specify the network adapter or
adapters that the DHCP server will use to
service clients.
 If your DHCP server is multi-homed, this
page gives you an opportunity to limit
DHCP service to network only.

 Provides you an opportunity to configure
the 015 domain names and the 006 DNS
Servers options for all scopes that you will
create on the DHCP server.
 The 015 DNS Domain Names option
▪ enables you to set a DNS suffix for the client connections obtaining an
address lease from the DHCP server.
 The 006 DNS Servers option
▪ enable you to configure a DNS server address list for the client
connections obtaining an addresses lease from the DHCP server.

 Enables you to configure the 044 WINS/
NBNS Server option
 So you can assign a WINS server list to clients.

 Enables you to define or edit scopes on the
DHCP server.
 A scope is an administrative grouping of IP
addresses for computers on a subnet that use
the DHCP service.
 Each subnet can have only a single DHCP scope
with a single continuous range of IP addresses.

 Scope Name
 Use to label the scope as it appears in the DHCP console.
 Starting and Ending IP Address
 You should use the consecutive addresses that makeup the subnet for
which you are enabling the DHCP service.
 You should be sure to exclude from this defined range any statically
assigned addresses for existing or planned servers on your network.
▪ For example, on the same subnet you need to assign a static IP address to the local DHCP
server, router (default gateway), and any DNS servers, WINS servers, and domain controllers.
 To exclude addresses, you can simply choose to limit the scope range so
that it does not include any of static addresses assigned to servers.
▪ For example, in the subnet 192.168.0.0/24 you can keep the addresses 192.168.0.1 through
192.168.0.20 for your statically addressed servers.
▪ You can then define the addresses 192.168.0.21 through 192.168.0.254 as the range for the
subnet’s DHCP scope.

 Subnet Mask
 The subnet mask that will be assigned to DHCP clients that receive
an address lease through this scope.
 Be sure to choose the same subnet mask as the one configured for
the DHCP server itself.
 Default Gateway (optional)
 Enables you to configure the 003 router option. Which assigns a
default gateway address to the DHCP clients that receive an address
lease through this scope.
 Subnet Type
 Allows you to assign one of two lease durations to the scope.
 By default, the scope is set to the wired subnet type, which
configure a lease duration of six days. The alternative setting is
wireless, for which the lease duration is eight hours.
 Activate This Scope
 A scope will lease out addresses only if it is activated.

 DHCPv6 refers to DHCP for IPv6
 Stateless mode
 the default addressing mode for IPv6 hosts in which
addresses are configured without the help of a DHCP
server while options can still be obtained from the DHCP
server.
 On the configure DHCPv6 Stateless Mode page
 you can disable stateless mode on the DHCP server and
enable to response to IPv6 hosts that has been enabled
for stateful addressing.
 Disable stateless addressing on the DHCP server
 you will later need to create a scope for an IPv6 address
range by using the DHCP console.

 To enable stateful addressing on an IPv6
host
 type the following command:
▪ netsh interface ipv6 set interface interface_name managedaddress=disabled

 To enable the IPv6 host to obtain DHCP
options from a DHCPv6 server
 type the following command:
▪ netch interface ipv6 set interface interface_name otherstateful=enabled

 It is unlikely that you will see any questions
about DHCPv6 on the 70-642 exam.

 When you leave the enable DHCPv6
Stateless Mode for this Server option
selected
 The configure IPv6 DNS Server Setting page
appears.

 Gives you an opportunity to authorize a
DHCP server for use in an Active Directory
domain.
 In Active Directory domain environments
 A DHCP server will not issue IP addresses to
clients unless the server is authorized.
 Requiring servers to be authorized reduces the
risk that a user will accidentally or intentionally
create a DHCP server that assigns invalid IP
address configurations to DHCP clients.

 (fill in the blanks.) Before a DHCP server in
a domain environment can lease addresses
from an existing scope to any DHCP clients,
you first need to……………the server and
…………the scope.
 Quick Check Answer:
 Authorize
 Activate

 Problems with DHCP configurations can
show up on the client side.
 These problems might include the
following:
 The client fails to obtain an IP address.
 There are address conflicts.
 The client obtains an address from the wrong
scope.

 When clicked, the Repair button performs a series of
specific actions:
 If the network connection is configured as a DHCP client, the
current settings are released, and a DHCPREQUEST message
is broadcast in an attempt to obtain new IP settings.
▪ This is the functional equivalent to performing an ipconfig /release
and ipconfig /renew.
 The ARP cache is flushed, as with the arp -d * command.
 The NetBIOS cache is flushed, as if the nbtstat -R command.
 The DNS cache is flushed, as if ipconfig /flushdns command.
 The client’s NetBIOS name and IP address are reregistered
with the WINS server, as if nbtstat -RR was entered.
 The client is reregistered with DNS as if ipconfig /registerdns
command.

 Understand the four stages of the DHCP process
 Know how to install and authorize a DHCP server
 Know how to create a DHCP scope
 Understand how relay agents help with multiple
physical network segments
 Understand the difference between exclusions and
reservations
 Understand what a IPv4 superscope is used for
 Understand how to integrate IPv4 Dynamic DNS
with DHCP
 Understand how to troubleshoot DHCP problems

Lesson 6: Dynamic Host Configuration Protocol A

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Lesson 6: Dynamic Host Configuration Protocol A