Exploring DHCP server options


By now we’ve installed the Dynamic Host Control Protocol service on our Windows Server edition, in this article we will explore DHCP properties. If you’ve just stumbled upon this article please take some time to read the previous post just to get additional information regarding this service. After installing the DHCP role on your Windows Server, you can further configure this service to achieve the desired result. That being said, you can set address reservations, configure scope options, create filters, view address leases etc.
In the last article we’ve deployed the DHCP service and we have configured our IP scope. When defining the DHCP scope, you must set the first and last IP address that will be used by the server to assign IP addresses to network clients. Exclusion ranges can be set on the server to ensure that those particular IPs will not be allocated to DHCP clients. The server supports multiple contiguous exclusion ranges so, this gives you a better way to manage IP addresses. To configure an exclusion scope open the DHCP console, navigate to the scope section under IPv4, right click the address pool and select new exclusion range:
DHCP exclusion range
Enter the first and last IP address from the exclusion range and press OK. The new exclusion scope will appear in the address pool section:
DHCP Address pool
You can also configure a superscope By using a superscope, you can group multiple scopes as a single administrative entity” (check the following link from Microsoft’s website). To configure a superscope right click the IPv4 section and select New Superscope:
DHCP Superscope
 
Enter the superscope name and the managed scopes:
Superscope
The newly created superscope will appear in the DHCP console and will managed the included scopes :
DHCP superscope
A multicast scope can be configured to define groups of multicast clients. Masticating is a mechanism in which a message is send to multiple predefined machines. When configuring a multicast group, you’ll have to set the first and last IP address that will be used by the multicast group. Right click the IPv4 menu, select New Multicast Scope  and follow the wizard. After you finish the wizard, the new multicast scope will appear in the DHCP console:
Multicast Scope
Read more about DHCP multicast scopes in this article from Microsoft’s website.
Now let’s explore the scope properties. Under the IPv4 section right click the DHCP scope and select Properties:
DHCP Scope properties
From this section we can modify the lease duration for DHCP clients from 8 days (the default value) to any value desired. After an IP lease has expired, the server will return the IP address to the DHCP Scope:
DHCP Lease duration
In the DNS section, you can setup the DHCP server to automatically update authoritative DNS servers with the host (A) and pointer (PTR) record of DHCP clients.There are several options available here:
DHCP properties
By default, the DHCP server will dynamically update A and PTR records if requested by DHCP clients and will discard these records when the IP lease is deleted. You can disable these settings if desired. In the name protection section you can enable the DHCP server to register A and PTR records on behalf of the client:
name protection
In the Network Access Protection, you can configure this feature for the IP scope. You can use the default profile or a custom profile. We will learn more about NAP in a future article. In the advanced section, further settings like delay can be configured:
DHCP Network Access Protection
In the address leases section you can view the currently leased IP addresses. The computer name, IP address, lease expiration time and IDs can be view from this panel:
DHCP address leases
From the DHCP console you can also configure IP reservations. When creating a reservation, that particular IP address will always be assigned to the configured host. The reservation is a mapping between MAC and IP address. When a client will try to obtain an IP address, the DHCP server will also check its database to see if there is a reservation for that particular host. A reservation can be made either from the address leases section by right clicking on one of the hosts or from the reservation section. Right click the reservation folder and select new reservation:
DHCP reservation
 
Enter the specified information and press add, the newly created reservation will appear in the console. This is a time consuming operation because each reservation must be configured individually.
Further DHCP options can be configured on the server level, on the scope level or on the reservation level. Where you define and configure these options depends on where they are applied. To explore additional server options, right click the section where you want to configure options and select configure options :
DHCP options
There are many configurable options available in this menu. On the right side of the menu you can read a short description of each option.
  • 003 Router – in this section you configure the gateway router that will be used by DHCP clients. You will add a router configuration when installing the DHCP role.
  • 006 DNS Servers – DNS servers used by clients for name resolution. In the installation wizard of the DHCP service you can configure two DNS servers that will be used by clients. In this section you can specify multiple DNS servers.
  • in the 007 and 008 you can specify the Log or Cookie Servers if you are using such devices within your network.
  • 015 DNS Domain Name – the primary suffix domain name used by clients.
I’ll let you explore all the options available here, they are so many and a bunch of them are rarely used. If you are using NNTP, WWW, IRC, SMTP or NTP servers you can also configure them using these options. To add a new dedicated server for one of the services indicated here you just have to type in the IP address or FQDN and press add:
DHCP DNS Severs
On the advanced tab you can view similar settings applied for different vendor or user classes:
Vendor class
DHCP classes are groups of defined clients that follow their own rules. That being said you can configure vendor specific or user specific classes for different groups of network clients. Vendor specific classes define computers that use a specific OS like legacy Windows 2000 or 98 or for standard Microsoft Windows Clients (XP, Vista, 7 or 8). User specific classes apply to network clients that use BOOTP, Network Access Protection or Remote Access Class. By default, all clients will belong to the Default User Class. To configure an user or a vendor specific class, right click the IPv4 section and select Define Users Classes or Define Vendor Classes:
Define Users Classes
 
Select the desired class and press ADD. In the New Class section type in the Display name, description and ID (a hexadecimal string defining the unique identification):
DHCP user class
After you press OK, the class will appear in the class section. If we navigate to the advanced options on the server options menu, we can view and configure the newly created user class:
DHCP user class
Now we can configure specific DHCP options for this class.
On a Windows client you’ll have to define the network class used. Open an elevated command prompt and  type in the following:
ipconfig /setclassid [interface_name] [class_name]
On one of my Windows 7 clients I’ve configured the newly created class:
DHCP Class id
You’ll have to set the class id on all of the clients using that particular class.
That’s it for this article folks, hope you’ve enjoy it. Wish you a great day and stay tuned for the following article from  IT training day.
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