Install DHCP Server Service, DHCP Scopes & Superscopes

Jocelyn Tanner

Installing the DHCP Server ServicePrior to installing the DHCP service, you must log on as administrator from the primary domain controller. To install the DHCP Server service, follow these steps:

1. Run Control Panel and choose Network.

2. Choose Add Software.

3. In the Add Network Software dialog box, select TCP/IP Protocol And Related Components, and then choose Continue.

The Windows NT TCP/IP Installation Options dialog box appears, displaying the TCP/IP components available to be installed.

4. Select DHCP Server Service, and then choose Continue.

Installing the DHCP Server Service

• The Windows NT setup box appears, prompting you for the full path of the Windows NT distribution files.

NOTE: You may be prompted with the following message:

At least one of your adapters has automatic DHCP configuration enabled. In order to correctly install the DHCP server, setup will disable automatic DHCP configuration. Are you sure you want to install the DHCP Server?

Choose Continue.

Installing the DHCP Server Service5. Type the path to the location of Windows NT Server distribution files, and choose Continue.

If you install from compact disc, the path is under the \I386 directory.

The TCP/IP configuration Box appears.

6. Enter the static IP address of the DHCP Server as well as the subnet mask and the default gateway. If you use Windows Internet Name Service (WINS), add the primary and secondary WINS addresses here.

The appropriate files are copied to your server, and then the Network Settings dialog box appears.

7. Choose OK.

A Network Settings Change dialog box appears, indicating that the system must be restarted to initialize the new configuration.

Installing the DHCP Server Service

8. Save any unsaved work in other windows and choose Restart Now to restart Windows NT Server.

9. Log on as Administrator.

Configuring a DHCP Scope

• Be sure to install and initialize the DHCP Server before completing the next step.

To configure the DHCP scope, you must log on as administrator. Configuring the DHCP scope supplies the DHCP client with the range of IP addresses from which the server draws from and a subnet mask to be assigned to clients.

Configuring a DHCP Scope

• The DHCP Server provides: Default gateway address

• Domain Name • Service server addresses • WINS server addresses • NETBIOS name resolution type.• Option 150 (TFTP servers for VoIP/VoSIP)

Configuring a DHCP Scope

1. From the Network Administration group, start DHCP Manager.

The DHCP Manager window appears. 2. Under DHCP Servers, select *Local Machine*

Local Machine indicates that you are configuring the local DHCP server, and not a remote DHCP server.

3. From the Scope menu, choose Create.

The Create Scope dialog box appears.

Configuring a DHCP Scope

4. Complete the scope configuration.

The DHCP server cannot be a DHCP client. It must have a static IP address, subnet mask, and default gateway address. You also have the option of assigning an exclusion range or specific excluded addresses as well as lease duration and a name.

5. Choose OK when done.

Configuring a DHCP Scope

6. Choose Yes to activate the scope.

The DHCP Manager window appears with the new scope added. Notice the yellow light bulb next to the IP address. This indicates an active scope.

7. Close the DHCP Manager.

Enabling DHCP at the Client

• To enable DHCP on a Windows for Workgroups client if TCP/IP is not installed yet: Use Network Setup to install the MS TCP/IP-32 3.11 protocol.

• In the MS TCP/IP Configuration dialog box, select the Enable Automatic DHCP Configuration check box, and choose Continue.

• Restart the computer to initialize TCP/IP using DHCP.

What is a DHCP Scope?

• A DHCP scope is an administrative grouping of computers running the DHCP Client service. You create a scope for each subnet on the network to define parameters for that subnet.

Each scope has the following properties: 1. A unique subnet mask to determine the subnet related to a

given IP address. 2. A scope name assigned by the administrator when the scope

is created. 3. Lease duration values to be assigned to DHCP clients with

dynamic addresses.

Using the DHCP Manager to Create, Manage or Remove scopes

• The DHCP database file (Dhcp.mdb) is a JET database that cannot be read by Microsoft Access or other application editors.

To create a new DHCP scope, select the server in the DHCP Manager window, and on the Scope menu, click Create.

A pop-up window is displayed requiring all necessary information to configure the DHCP Server. To configure the new scope, type the appropriate information into the following fields:

IP Address Pool• IP Address Pool

Field Description ------------------------------------------------------------------------------------

Start address -- Specifies the first IP address of the scope for the clients

End address -- Specifies the last IP address of the scope for the clients

Subnet mask -- Specifies the subnet mask for the client subnet

Exclusion Range

• By specifying addresses to be excluded from a range, DHCP Manager will not lease these addresses to requesting clients. An example of this is a UNIX Tower or similar machine that cannot be reconfigured with a static IP address outside of the intended/defined scope (for example, a corporate DNS).

To implement several address scopes within one subnet on a single DHCP server, create one continuous IP address range that includes all available addresses within the subnet. Then, exclude necessary addresses or ranges from within the defined scope.

Example of Exclusion Range

• Defined scope: 192.192.192.1 through 192.192.192.200

• Excluded: 192.192.192.5 and 192.192.192.10 through 192.192.192.50

• Available addresses: 192.192.192.1 through 192.192.192.4, 192.192.192.6 through 192.192.192.9, and 192.192.192.51 through 192.192.192.200

Lease Duration

Lease Duration Unlimited• This option specifies that the DHCP lease

assigned to a client will never expire. This is not a recommended option and should be substituted through the use of client reservations.

Lease Duration Limited to• The number of days, hours, and minutes that a

DHCP client lease is available before it must be renewed.

Name & Comment

Name• The scope name is the name that describes

this subnet and is displayed after the IP address in DHCP Manager. The name can include any combination of letters, numbers, hyphens, underscores, or blank characters.

Comment• This is an optional field.

Configuring Superscopes• The enhanced DHCP server allows the administrator to create different scopes

(ranges of IP addresses), and then to group those scopes together into a superscope.

• To create a superscope, complete the following steps:

1. Create each of the scopes using DHCP Manager. Assign global and scope properties as desired. Be sure to enable each scope.

2. In DHCP Manager, select the DHCP server. Click Scope, and then click Superscopes.

3. Click Create Superscope, supply a name for the superscope, and then click OK.

DHCP Option 150 (TFTP servers)

Add the TFTP Option to the Scope • Cisco IP Phones expect the DHCP server to

also provide the IP address of the TFTP server. By default, the TFTP option is not available in a newly defined DHCP scope. Complete these steps in order to add the TFTP option to the scope.

DHCP Option 150 (TFTP servers)1. Right-click the server and select Set

Predefined Options, then click Add

DHCP Option 150 (TFTP servers)2. Enter the Name as TFTP Server IP Address, Data Type is IP Address,

Code is 150, and Description is TFTP Server IP Address for CallManager Devices.

DHCP Option 150 (TFTP servers)3. Click OK and then Edit Array. Enter the IP address(es) for TFTP server(s)

that are normally housed on the Cisco CallManager systems.

DHCP Option 150 (TFTP servers)

4. Click OK twice in order to complete the creation of Option 150. Under the new Cisco CallManager DHCP Scope you created is a field labeled "Scope Options". If you right-click Scope Options and select Configure Options, you can select Option 150 as an option to hand out to Devices.

DHCP Option 150 (TFTP servers)

5. Click Apply and OK in order to see that the scope now has Option 150.

6. Right-click the Scope and select Activate in order to activate the Scope.

Configuring Superscopes

4. Add the appropriate scopes from the Available Scopes list to the Child Sub-Scopes list.

When finished, the Child Scopes should be listed from top to bottom in the order that you want addresses to be used from them.

NOTE: The order that you add the Child Sub-Scopes is of no consequence. DHCP Manager will sort them in ascending order.

5. Click OK.

Configuring Superscopes

6. If the DHCP server is configured with the IgnorebroadcastFlag DHCP Registry value set to 0, and if the Superscope is on a subnet that is directly attached to the server (that is, not being reached via a DHCP relay agent), then each of the logical subnets must be directly reachable by the DHCP server.

This means that there must be a local route to each logical subnet. The easiest way to accomplish this is to add an IP address to the NIC on the local server for each of the logical subnets that it is attached to.

IgnorebroadcastFlag DHCP Registry Information

• Versions of the DHCP server prior to Windows NT 4.0 ignored the broadcast flag in client DHCP packets, and broadcast all replies. Version 4.0 of the DHCP server supports unicasting via the following registry parameter:

•HKEY_LOCAL_MACHINE \CurrentControlSet \Services \DHCPServer \Parameters \IgnoreBroadcastFlag Parameter Type: REG_DWORDDefault: 1

• Description: If set to 1, the broadcast flag in client requests is ignored, and all DHCP packets are broadcast from the server. If set to 0, the behavior (whether to broadcast or not) is controlled by the broadcast flag in the client request that is being responded to.

• The Networks.wri file also contains a description of this parameter.

Questions!