AN Lesson-3

 Configuring DHCP Server

Q.         What is the use of reservation in a DHCP service? And discuss how to create a reservation?

        i)            Exclusion Ranges

• An exclusion range is a set of one or more IP addresses, included within the range of a defined scope, that you do not want to lease to DHCP clients. Exclusion ranges assure that the server does not offer to DHCP clients on your network any addresses in these ranges. 
• For example, Figure below shows two exclusion ranges being configured for a new scope, one  of which consist of only one IP address. By setting an exclusion for these addresses, you specify that DHCP clients are never offered these addresses when they request a lease from the server.

  

  ii)            80/20 Rule for Scopes

To provide fault tolerance for the DHCP service within a given subnet For balancing DHCP server use a good practice is to use the 80/20 rule to divide the scope addresses between the two DHCP servers. If Server 1 is configured to make available most (approximately 80 percent) of the addresses, Server 2 can be configured to make the other addresses (approximately 20 percent) available to clients.

iii)        Creating Reservations

• You use a reservation to create a permanent address lease assignment by the DHCP server. Reservations assure that a specified hardware device on the subnet can always use the same IP address.
•  For example, if you have defined the range 192.168.1.11 through 192.168.1.254 as your DHCP scope, you can then reserve the IP address 192.168.1.100 within that scope for the network adapter whose hardware address is 00-b0-d0-01-18-86.

To create a reservation within the DHCP console,

1. Open the scope in which you want to create a reservation.
2. Right-click Reservations
3. Then select New Reservation. This procedure opens the New Reservation dialog box, shown in Figure below.
4. To configure a reservation, you must type appropriate values into the Reservation Name, IP Address,and MAC Address text boxes.

5.  Reservations cannot be used interchangeably with manual (static)configurations.Certain computers,   such as those hosting a DNS server or a DHCP server, require their IP addresses to be configured manually and not automatically by means of a DHCP server. In such cases, reservations are not a valid alternative to static configurations.

iv)        Assigning DHCP Options

1. DHCP options provide clients with additional configuration data, such as specific server addresses, along with an address lease.

2. You can configure options at the reservation level, scope level, or server level. Options set at the reservation level override all others, and scope-level options override server level options.

v)         Activating a Scope

After you define and configure a scope, the scope must be activated before the DHCP

server can begin providing service to clients. However, you should not activate a new

scope until you have specified the DHCP options for it.

To activate a scope, complete the following steps:

1. Open the DHCP console.

2. In the console tree, select the applicable scope.

3. From the Action menu, select Activate.