Mahmmoud A. Mahdi
DHCP allows you to assign IP addresses, subnet masks, and other configuration 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 Configuration Protocol
Automatic configuration ▪
IP address
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Subnet mask
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Other Information
Requires DHCP Server
Windows Server 2008 Role
Configuration of large and even midsize networks is much simpler. simpler. Once you enter the IP configuration information in one place(the server) it’s automatically propagated propagated to clients, eliminating the risk that 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. automatic. Allows a preboot execution environment (PXE) environment (PXE) client to get a TCP/IP address from DHCP.
PXE clients (also called Microsoft Remote Installation Services 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 DHC P 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 configuration protocol (DHCP).
Installing Installing DHCP server. server. 2. Configuring Configuring a DHCP server. server. 1.
Installing 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 wi th DHCP Offer O ffer.. 3. Respond with DHCP Request. 4. Confirm with DHCP Ask.
1. Broadcast DHCPISCOVER DHCPISCOVER 2. Respond with DHCPOFFER 3. Respond with DHCPREQUEST 4. Confirm with DHCPACK
Every Every DHCP server maintains a database of addresses that the server can distribute d istribute 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 from the network , DHCP server reclaim reclaim addresses at the end of the DHCP lease period.
If the DHCP server is online online ▪
If the DHCP server is not available ▪
Accept the renewal 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 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 client until the DHCP lease expires.
ipconfig /renew
Instructs the DHCP client to request a lease renewal. ▪
▪
ipconfig /release
If the client already has a lease, it requests a renewal from the server that issued the current lease. if the client cli ent doesn’t currently have have a lease, lease, It initiates the DHCP mating dance, listens for lease offers, and chooses one it likes.
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 snap-in allows you to manage IP address assignment in the superscope, though you must still configure other scope s cope options individually for each child scope.
Exclusions and Reservations Reservations
Address Pool Pool
are IP addresses within the range that you never 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.
Exclusions
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. exam.
DHCP options provide clients with additional configuration configuration parameters 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: ▪
006 DNS Servers: ▪
▪
Used to provide the DNS suffix Allows clients to perform dynamic DNS updates.
044 WINS/ NBNS Servers: ▪
Used to provide a list of DNS servers
015 DNS Domain Name: ▪
Used to provide a list of available available routers or default gateways on the same subnet
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: ▪
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▪
▪
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. 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 b e compatible with the address range range planned for the local subnet. Use the add roles wizard to add the DHCP server role on the computer. computer.
The wizard presents you with the following following configuration configuration pages: 1. Select network connection bindings. 2. Specify IPv4 DNS Server Server settings.
Server settings. 3. Specify IPv4 WINS Server 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 service to network only. only.
Provides you an opportunity to configure the 015 domain names and the 006 DNS Servers 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 server..
A scope is an administrative grouping of IP addresses 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 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, server, router (default gateway), and any DNS D NS 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, example, in the subnet 192.168.0.0/24 you can keep the addresses 192.168.0.1 through 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
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
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.
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 Activate This Scope
A scope will lease out addresses only if it is activated.
DHCPv6 refers to DHCP for IPv6 Stateless mode
On the configure DHCPv6 Stateless Mode page
the default addressing mode for IPv6 hosts in which addresses are configured configured without the help of a DHCP server while options can still be obtained from the DHCP server. 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 set interface interface interface_name otherstateful=enabled
It is unlikely that you will see any questions about DHCPv6 on the 70-642 exam. 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 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. /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 if ipconfig /flushdns command. The client’s NetBIOS name and IP address are reregistered reregistered with the WINS server, as if nbtstat if nbtstat -RR was entered. The client is reregistered with DNS as if ipconfig if ipconfig /register /registerdns dns 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
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