Contents for DHCP Manager Help

How To

 Using DHCP Manager

 Defining DHCP Scopes

 Administering DHCP Clients

 Configuring DHCP Option Types

Commands

 Server Menu Commands

 Scope Menu Commands

 DHCP Options Menu Commands

 View Menu Commands


Contents -- All Topics
Contents for DHCP Manager Help

How To

 Using DHCP Manager

 Introduction to DHCP Servers

 Overview of DHCP Clients and Servers

 Starting DHCP Manager

 Starting and Stopping the DHCP Server Service

 Defining DHCP Scopes

 Introduction to DHCP Scopes

 Creating Scopes

 Changing Scope Properties

 Removing a Scope

 Administering DHCP Clients

 Introduction to Administering DHCP clients

 Managing Client Leases

 Managing Client Reservations

 Configuring DHCP Option Types

 Introduction to DHCP Option Types

 Assigning DHCP Configuration Options

 Adding New Option Types

 Changing Option Values

 Defining Options for Reservations

 Predefined DHCP Client Configuration Options

Commands

 Server Menu Commands

 Add

 Remove

 Exit

 Scope Menu Commands

 Create

 Properties

 Activate and Deactivate

 Delete

 Add Reservations

 Active Leases

 DHCP Options Menu Commands

 Global

 Scope

 Defaults

 View Menu Commands

 Next Pane

 Split

 Status Bar


Contents for DHCP Manager Help

How To

 Using DHCP Manager

 Introduction to DHCP Servers

 Overview of DHCP Clients and Servers

 Starting DHCP Manager

 Starting and Stopping the DHCP Server Service

 Defining DHCP Scopes

 Administering DHCP Clients

 Configuring DHCP Option Types

Commands

 Server Menu Commands

 Scope Menu Commands

 DHCP Options Menu Commands

 View Menu Commands


Contents for DHCP Manager Help

How To

 Using DHCP Manager

 Defining DHCP Scopes

 Introduction to DHCP Scopes

 Creating Scopes

 Changing Scope Properties

 Removing a Scope

 Administering DHCP Clients

 Configuring DHCP Option Types

Commands

 Server Menu Commands

 Scope Menu Commands

 DHCP Options Menu Commands

 View Menu Commands


Contents for DHCP Manager Help

How To

 Using DHCP Manager

 Defining DHCP Scopes

 Administering DHCP Clients

 Introduction to Administering DHCP clients

 Managing Client Leases

 Managing Client Reservations

 Configuring DHCP Option Types

Commands

 Server Menu Commands

 Scope Menu Commands

 DHCP Options Menu Commands

 View Menu Commands


Contents for DHCP Manager Help

How To

 Using DHCP Manager

 Defining DHCP Scopes

 Administering DHCP Clients

 Configuring DHCP Option Types

 Introduction to DHCP Option Types

 Assigning DHCP Configuration Options

 Adding New Option Types

 Changing Option Values

 Defining Options for Reservations

 Predefined DHCP Client Configuration Options

Commands

 Server Menu Commands

 Scope Menu Commands

 DHCP Options Menu Commands

 View Menu Commands


Contents for DHCP Manager Help

How To

 Using DHCP Manager

 Defining DHCP Scopes

 Administering DHCP Clients

 Configuring DHCP Option Types

Commands

 Server Menu Commands

 Add

 Remove

 Exit

 Scope Menu Commands

 DHCP Options Menu Commands

 View Menu Commands


Contents for DHCP Manager Help

How To

 Using DHCP Manager

 Defining DHCP Scopes

 Administering DHCP Clients

 Configuring DHCP Option Types

Commands

 Server Menu Commands

 Scope Menu Commands

 DHCP Options Menu Commands

 View Menu Commands

 Next Pane

 Split

 Status Bar


Contents for DHCP Manager Help

How To

 Using DHCP Manager

 Defining DHCP Scopes

 Administering DHCP Clients

 Configuring DHCP Option Types

Commands

 Server Menu Commands

 Scope Menu Commands

 Create

 Properties

 Activate and Deactivate

 Delete

 Add Reservations

 Active Leases

 DHCP Options Menu Commands

 View Menu Commands


Contents for DHCP Manager Help

How To

 Using DHCP Manager

 Defining DHCP Scopes

 Administering DHCP Clients

 Configuring DHCP Option Types

Commands

 Server Menu Commands

 Scope Menu Commands

 DHCP Options Menu Commands

 Global

 Scope

 Defaults

 View Menu Commands


Exit

Quits DHCP Manager.


Activate and Deactivate

Activate starts lease distribution and deactivate starts lease recall on the selected scope. The command name becomes Deactivate when the scope is activated, and becomes Activate when the scope is deactivated.

You must activate a scope to make it available for use by DHCP clients. Do not activate a scope until all the desired options have been specified for the scope.

You must deactivate a scope before deleting it to enable the DHCP clients using the scope to seek leases for their IP addresses on another scope on the subnet. Otherwise, the clients lose their leases. The DHCP server sends NACKs (negative acknowledgments) to DHCP clients that seek renewals of their leases from the deactivated scope. When the DHCP clients receive the NACKs, the clients return to the initialization phase and attempt to acquire new IP address leases from another active scope on the subnet.

Important

Before deactivating a scope, a replacement scope should be active on the subnet. The replacement scope can be on a different DHCP server than the deactivated scope as long as the replacement scope is on the same subnet.

Do not use Deactivate to pause a scope. Deactivate should be used only before deleting a scope.

By the time that a scope has been deactivated for half its lease time, all clients that are up and running should have been forced to seek leases from the other active scope on the DHCP server.


Scope

An administrative grouping of computers running the DHCP Client service. The administrator creates a scope for each subnet on the network to define parameters for that subnet. A scope has the following properties:

A unique subnet mask to determine the subnet related to a given IP address

A scope name assigned when the scope is created

Lease duration values to be assigned to DHCP clients that receive dynamically allocated IP addresses


Delete

Deletes the selected scope.


Installing and Configuring DHCP Servers
Introduction to DHCP Servers

A Dynamic Host Configuration Protocol (DHCP) server is a Windows NT Server computer running Microsoft TCP/IP and the DHCP server software. DHCP is defined in Requests for Comments (RFCs) 1533, 1534, 1541, and 1542. Configuring DHCP servers for a network provides these benefits:

The administrator can centrally specify global and subnet-specific TCP/IP parameters for the entire internetwork and define parameters for clients using reserved addresses.

Client computers do not require manual TCP/IP configuration. When a client computer moves between subnets, it is reconfigured for TCP/IP automatically when the computer is started.

Important:

If you want to use a DHCP server to support subnetworks that span multiple routers, you may need a firmware upgrade for your routers. Your routers must support RFCs 1533, 1534, 1541, and 1542. To find out about DHCP-relay agent support, contact your router vendor. For more information, refer to RFC1542.TXT available via anonymous FTP from ftp.internic.net:/rfc.

The following topic describes using servers to support the DHCP capabilities in Windows NT :

 Overview of DHCP Clients and Servers

See Also

Dynamic Host Configuration Protocol


Overview of DHCP Client-Server Model
Overview of DHCP Clients and Servers

DHCP uses a client-server model. The network administrator establishes one or more DHCP servers that maintain TCP/IP configuration information and provide it to clients. The server database includes the following:

Valid configuration parameters for all clients on the internetwork.

Valid IP addresses maintained in a pool for assignment to clients, plus reserved addresses for manual assignment.

Duration of leases offered by the server. The lease defines the length of time for which the assigned IP address can be used.

A Windows NT computer becomes a DHCP client if the Enable Automatic DHCP Configuration option is checked in the Windows NT TCP/IP Installation dialog box. When a DHCP client computer is started, it communicates with a DHCP server to receive the required TCP/IP configuration information. This configuration information includes at least an IP address and submask plus the lease associated with the configuration.

Configuring DHCP servers for a network provides these benefits:

The administrator can specify global and subnet-specific TCP/IP parameters centrally for the entire internetwork.

Client computers do not require manual TCP/IP configuration.

When a client computer moves between subnets, the old IP address is freed for reuse, and the client is reconfigured for TCP/IP automatically when the computer is started.

Most routers can forward DHCP configuration requests, so DHCP servers are not required on every subnet in the internetwork.


Lease

The length of time for which a dynamically assigned IP address can be used. Before the lease expires, the DHCP client must renew the lease with the DHCP server.


Using DHCP Administrator
Using DHCP Manager

The DHCP Manager icon is added to Program Manager when you set up a Windows NT Server computer to be a DHCP server.

After you install a DHCP server, you must use DHCP Manager to perform these basic tasks:

 Create DHCP scopes

This performs all the tasks necessary to begin providing DHCP services.

 Define properties for scopes

This includes the IP address ranges to be distributed to potential DHCP clients by servers in the scope.

 Configure DHCP Option Types

This includes defining default values for DHCP options such as lease durations, or add any custom options.

Important:

When you are working with DHCP Manager, all computer names are Domain Name System (DNS) names only. The full path specification may be used, such as accounting.trey.com, or a name may be specified relative to the local domain. In the previous example, other computers in the trey.com DNS domain can refer simply to accounting. The DNS host name is not necessarily the same as the NetBIOS computer name used in Windows NT networking.


DHCP Option

The configuration parameters that a DHCP server assigns to a client. Most options are predefined, based on the parameters defined in RFC 1542. The administrator assigns options by choosing commands from the DHCP Options menu.


Starting DHCP Administrator
Starting DHCP Manager

To start DHCP Manager

Double-click the DHCP Manager icon in Program Manager.

- Or -

At the command prompt, type start dhcpadmn and press Enter.

You automatically connect to the servers and scopes to which you were last connected. The DHCP Manager window shows a list of the scopes for the current server. You can connect to additional servers.

To connect to a DHCP server

1.	From the Server menu, choose the Add command.

2.	In the Add DHCP Server To Known Server List dialog box, type the DNS short name or IP address for the DHCP server you want to connect to, and then choose the OK button.

For example, type an address such as 11.1.26.30 or type a DNS name such as corp01.trey.com in this box.

To disconnect from a selected DHCP server

From the Server menu, choose the Remove command.

Important:

When you are working with DHCP Manager, all computer names are DNS names only, such as accounting.trey.com. The NetBIOS computer names used in Windows networking are not allowed.


Starting and Stopping the DHCP Service
Starting and Stopping the DHCP Server Service

To start or stop the DHCP server service

1.	In Control Panel, choose the Services icon.

-Or-

In Server Manager, choose Services from the Computer menu.

2.	In the Services dialog box, select the Microsoft DHCP Server service.

3.	Choose the Start, Stop, Pause or Continue button, and then choose the Close button.

By default, the Microsoft DHCP Server service starts automatically when the computer is started.


Defining DHCP Administrative Scopes
Introduction to DHCP Scopes

A DHCP scope is a grouping of computers running the DHCP client service in a subnet. The scope is used to define parameters for each subnet.

Each scope has the following properties:

A unique subnet mask used to determine the subnet related to a given IP address.

A scope name assigned by the administrator when the scope is created.

Lease duration values to be assigned to DHCP clients with dynamic addresses.

See Also

Creating Scopes

Changing Scope Properties

Removing a Scope


Creating Administrative Scopes
Creating Scopes

You must use DHCP Manager to create, manage, or remove scopes.

To create a new DHCP scope

1.	In the DHCP Servers list in the DHCP Manager window, select the server for which you want to create a scope.

2.	From the Scope menu, choose Create.

3.	To define the available range of IP addresses for the scope, type the beginning and ending IP addresses for the range in the Start Address and End Address boxes.

The IP address range includes the Start and End values. This range should not include addresses of existing statically configured computers. Either these static addresses should be outside the range for the scope, or they should be immediately excluded from the range. Because the DHCP server itself is statically configured, be sure that its IP address is outside of, or excluded from, the range of the scope.

Note:	You must supply this information to activate the scope on the primary server.

4.	In the Subnet Mask box, DHCP Manager proposes a subnet mask, based on values of the Start and End addresses. Accept the proposed value, unless you know that a different value is required.

5.	To define excluded addresses within the IP address pool range, use the Exclusion Range controls, as follows:

Type the first IP address that is part of the excluded range in the Start Address box, and type the last number in the End Address box. Then choose the Add button. Continue to define any other excluded ranges in the same way.

To exclude a single IP address, type the number in the Start Address box. Leave the End Address box empty.

To remove an IP address or a range from the excluded range, select it in the Excluded Addresses box, and then choose the Remove button.

The excluded ranges should include all IP addresses that you assigned manually to other DHCP servers, non-DHCP clients, diskless workstations, or RAS and PPP clients.

6.	To specify the lease duration for IP addresses in the scope, select Limited To. Then type values defining the number of days, hours, and seconds for the length of the address lease.

If you do not want IP address leases in the scope to expire, select Unlimited. Unlimited, or infinite, leases should be used with great caution.

7.	In the Name box, type a scope name of up to 128 characters.

This is any name you want to use to describe the subnet. The name can include any combination of letters, numbers, and hyphens.

8.	Optionally, in the Comment box, type any string to describe the scope, and then choose the OK button.

When you finish creating a scope, a message reminds you that the scope has not been activated and allows you to choose Yes to activate the scope immediately. However, you should not activate a new scope until you have specified the DHCP options for this scope.

To activate a DHCP scope

From the Scope menu, choose the Activate command to make this scope active.

The menu command name changes to Deactivate when the selected scope is currently activated.


Changing Properties for Administrative Scopes
Changing Scope Properties

The subnet identifiers and address pool make up the properties of scopes. You can change the properties of an existing scope.

You cannot exclude a range of addresses that includes an active lease. You must first delete the active lease, and then retry the exclusion.

To define the properties of a DHCP scope

1.	In the DHCP Servers list in the DHCP Manager window, select the scope for which you want to change properties, and then from the Scope menu, choose Properties.

Or, in the DHCP Servers list, double-click the scope you want to change.

2.	In the Scope Properties dialog box, change any values for the subnet identifier or primary server, or change values for the IP address pool, as described in Creating Scopes. You can extend the address range of the scope, but you cannot reduce it. You can, however, exclude any unwanted addresses from the range.

3.	Choose the OK button.

See Also

Managing Client Leases


Removing an Administrative Scope
Removing a Scope

When a subnet is no longer in use, or any other time you want to remove an existing scope, you can remove it using DHCP Manager. If any IP address in the scope is still leased or in use, you must first activate the scope until the clients lease expires or the clients lease extension request is denied.

When a scope is deactivated, it does not acknowledge lease or renewal requests, so existing clients lose their leases at renewal time and reconfigure with another available DHCP server. To assure that all clients migrate smoothly to a new scope, you should deactivate the old scope for at least half of the least time, or until all clients have been moved off the scope manually. To move a client manually, from the Command Prompt of the client computer use the ipconfig/renew command, and then restart the computer if necessary.

To remove a scope

1.	In the Scopes list in the DHCP Manager window, select the scope you want to remove.

2.	From the Scope menu, choose Deactivate. (This command name changes to Activate when the scope is deactivated.)

The scope must be deactivated until you are sure the scope is not in use.

3.	From the Scope menu, choose Delete.

The Delete command is not available until you deactivate the scope.


Configuring DHCP Option Types
Introduction to DHCP Option Types

The configuration parameters that a DHCP server assigns to a client are defined as DHCP options using DHCP Manager. Most options you will want to specify are predefined, based on standard parameters defined by the Internet Network Working Group in RFC 1541.

When you configure a DHCP scope, you can assign option types to govern all configuration parameters. You can also define, edit, or delete option types.

See Also

Assigning DHCP Configuration Options

Predefined DHCP Client Configuration Options

Adding New Option Types


Assigning DHCP Configuration Options

Besides the IP addressing information, other DHCP options to be passed to DHCP clients must be configured for each scope. Options can be defined globally for all scopes, specifically for a selected scope, or for individual DHCP clients.

Active global option types always apply, unless overridden by scope or DHCP client settings.

Active option types for a scope apply to all computers in that scope, unless overridden for an individual DHCP client.

The Microsoft DHCP network packet allocates 312 bytes for DHCP options. That is more than enough for most option configurations. With some DHCP servers and clients, you can allocate unused space in the DHCP packet to additional options. This feature, called option overlay, is not supported by Microsoft DHCP Server. If you attempt to use more than 312 bytes, some options settings will be lost. In that case, you should delete any unused or low-priority options.

If you are using a third-party DHCP server, be aware that Microsoft DHCP clients do not support options overlays, either. If your option set is larger than 312 bytes, be sure that the settings used by Microsoft DHCP clients are included at the beginning of the option list. Settings beyond the first 312 bytes are not read by Microsoft DHCP clients.

To assign DHCP configuration options

1.	In the DHCP Servers list in the DHCP Manager window, select the scope you want to configure.

2.	From the DHCP Options menu, choose the Global or Scope command, depending on whether you want to define option settings for all scopes on the currently selected server or the scope currently selected in the DHCP Manager window.

3.	In the Unused Options list in the DHCP Options dialog box, select the name of the DHCP option that you want to apply, and then choose the Add button to move the name to the Active Options list.

This list shows both predefined options and any custom options that you created. For example, if you want to specify DNS servers for computers, select the option named DNS Servers in the Unused Options list, and then choose the Add button.

If you want to remove a DHCP option that has been assigned for this class, select its name in the Active Options box, and then choose the Remove button.

4.	To define the value for an active option, select its name in the Active Options box, choose the Values button, and then edit the information in the Current Value box, depending on the data type for the option, as follows:

For an IP address, type the assigned address for the selected option.

For a number, type an appropriate decimal or hexadecimal value for the option.

For a string, type an appropriate ASCII string containing letters and numbers for the option.

For example, to specify the DNS name servers to be used by DHCP clients, select DNS Servers in the Active Options list, and then type a list of IP addresses for DNS servers in the Current Value box. The list should be in the order of preference, so that the first server in the list is the first server to be consulted.

5.	When you have completed all your changes, choose the OK button.


Changing Option Type Values
Changing Option Values

You can change the values for the predefined and custom DHCP option types.

Options that take an array of IP addresses have a default value of 0.0.0.0. You should reset the default value of any such options you intend to use, or be sure to set a different value when you assign the option either globally or for a selected scope as described in Assigning DHCP Configuration Options.

To change an option type value

1.	From the DHCP Options menu, choose Defaults.

2.	In the Option Class list in the DHCP Options: Default Values dialog box, select the option class for which you want to change values.

3.	If you want to change the default value for an option, select the option you want to change in the Option Name list, choose the Edit button, and then type a new value in the Default Value box.

Choosing the Edit button displays a special dialog box for editing strings, arrays of IP addresses, or binary values.

4.	If you want to change basic elements of a custom option, select it in the Option Name list, and then choose the Change button.

You can change the name, data type, identifier, and comment for an option type, following the procedures described earlier in Adding New Option Types.

5.	When you complete all the changes you want to make, choose the OK button.


Creating New Option Types
Adding New Option Types

You can add custom parameters to include with DHCP client configuration information. You can also change values or other elements of the predefined DHCP option types. The option you add will appear in the list of available option types in the Options Settings dialog boxes for defining options globally, per scope, and per individual DHCP client.

To add new option types

1.	From the DHCP Options menu, choose Defaults.

2.	In the Option Class list in the DHCP Options: Default Values dialog box, select the class for which you want to add new option types, and then choose the New button.

The option class can include the DHCP standard options or any custom options that you add.

3.	In the Name box of the Add Option Type dialog box, type a new option name.

4.	From the Data Type list, select the data type for this option as described in the following list. If the data type represents an array, check the Array box.

Binary = Value expressed as a binary array

Byte = An 8-bit, unsigned integer

Encapsulated = An array of unsigned bytes

IP address = An IP address of the form w.x.y.z

Long = A 32-bit, signed integer

Long integer = A 32-bit, unsigned integer

String = An ASCII text string

Word = A 16-bit, unsigned integer

5.	In the Identifier box, type a unique code number to associate with the option type.

Important:

Be careful to enter a unique number. DHCP Manager does not check for duplicate entries.

6.	In the Comment box, type a description of the option type, and then choose the OK button.

7.	In the Default Value box of the Default Option Values dialog box, type the value to be configured by default for this option type.

8.	Choose the OK button.

You can delete custom option types, but you cannot delete any predefined option types.

To delete an option type

1.	From the DHCP Options menu, choose Defaults. Or, in the Option Configuration list in the DHCP Manager window, double-click the option you want to change.

2.	In the DHCP Options: Default Values dialog box, select the related class in the Option Class list.

3.	In the Option Name list, select the option you want to delete, and then choose the Delete button.


Defining Options for Reservations

You can assign DHCP option types and specify custom values for DHCP clients that use reserved IP addresses. Reservations are created in the Add Reserved Client dialog box.

To change option types for reservations

1.	From the Scope menu, choose Active Leases.

2.	In the IP Address list of the Active Leases dialog box, select the reservation address that you want to change, and then choose the Options button. The Options button is only available for reserved addresses; it is not available for DHCP clients with dynamic addresses.

3.	In the DHCP Options: Reservation dialog box, select an option name in the Unused Options list, and then choose the Add button to move the name to the Active Options list.

If you want to remove an option type that has been assigned to the scope, select its name in the Active Options box, and then choose the Remove button.

4.	To change a value for an option selected in the Active Options list, choose the Value button, and then enter a value in the Current Value box.


Reservation

A specific IP address that is reserved for a specific DHCP client. An entry in the DHCP database is created for a reserved client by choosing the Add Reservation command from the Scope menu.


Predefined DHCP Configuration Options
Predefined DHCP Client Configuration Options

The following topics describe the predefined DHCP options provided for DHCP configuration, which are defined in RFC 1533.

 Basic Options

 IP Layer Parameters per Host

 IP Parameters per Interface

 Link Layer Parameters per Interface

 TCP Parameters

 Application Layer Parameters per Interface

 Vendor-Specific Information (NetBIOS over TCP/IP and X Window)


Basic Options

* = List is specified in order of preference, so that the first in the list is the first to be used.

You can use Microsoft DHCP Server to set any of the options whose code and option name are listed in italic type. If you have third-party DHCP clients, you can set any option listed that is supported by the third-party client software.

0 = Pad

Causes subsequent fields to align on word boundaries.

255 = End

Indicates end of options in the DHCP packet.

1 = Subnet mask

Specifies the subnet mask of the client subnet. This option is defined in the Create Scope or Scope Properties dialog box. It cannot be set directly in an Option dialog box.

2 = Time offset

Specifies the Universal Coordinated Time (UCT) offset in seconds.

3 = Router

Specifies a list of IP addresses for routers on the clients subnet.*

4 = Time server

Specifies a list of IP addresses for time servers available to the client.*

5 = Name servers

Specifies a list of IP addresses for name servers available to the client.*

6 = DNS servers

Specifies a list of IP addresses for DNS name servers available to the client.* Multihomed computers can have only one list per computer, not one per adapter card.

7 = Log servers

Specifies a list of IP addresses for MIT_LCS User Datagram Protocol (UDP) log servers available to the client.*

8 = Cookie servers

Specifies a list of IP addresses for RFC 865 cookie servers available to the client.*

9 = LPR servers

Specifies a list of IP addresses for RFC 1179 line-printer servers available to the client.*

10 = Impress servers

Specifies a list of IP addresses for Imagen Impress servers available to the client.*

11 = Resource location servers

Specifies a list of RFC 887 Resource Location servers available to the client.*

12 = Host name

Specifies the host name of up to 63 characters for the client. The name must start with a letter, end with a letter or digit, and have as interior characters only letters, numbers, and hyphens. The name can be qualified with the local DNS domain name.

13 = Boot file size

Specifies the size of the default boot image file for the client, in 512-octet blocks.

14 = Merit dump file

Specifies the ASCII path name of a file where the clients core image is dumped if a crash occurs.

15 = Domain name

Specifies the DNS domain name the client should use for DNS host name resolution.

16 = Swap server

Specifies the IP address of the clients swap server.

17 = Root path

Specifies the ASCII path name for the clients root disk.

18 = Extensions path

Specifies a file retrievable via TFTP containing information interpreted the same as the vendor-extension field in the BOOTP response, except the file length is unconstrained and references to Tag 18 in the file are ignored.


IP Layer Parameters per Host

The following lists IP layer parameters on a per-host basis.

19 = IP layer forwarding

Enables or disables forwarding of IP packet for this client. 1 enables forwarding; 0 disables it.

20 = Nonlocal source routing

Enables or disables forwarding of datagrams with nonlocal source routes. 1 enables forwarding; 0 disables it.

21 = Policy filter masks

Specifies policy filters that consist of a list of pairs of IP addresses and masks specifying destination/mask pairs for filtering nonlocal source routes. Any source routed datagram whose next-hop address does not match a filter will be discarded by the client.

22 = Max datagram reassembly size

Specifies the maximum size datagram that the client can reassemble. The minimum value is 576.

23 = Default time-to-live

Specifies the default time-to-live (TTL) that the client uses on outgoing datagrams. The value for the octet is a number between 1 and 255.

24 = Path MTU aging timeout

Specifies the timeout in seconds for aging Path Maximum Transmission Unit (MTU) values (discovered by the mechanism defined in RFC 1191).

25 = Path MTU plateau table

Specifies a table of Maximum Transmission Unit (MTU) sizes to use when performing Path MTU Discovered as defined in RFC 1191. The table is sorted by size from smallest to largest. The minimum MTU value is 68.


IP Parameters per Interface

The following lists IP parameters on a per-interface basis. These options affect the operation of the IP layer on a per-interface basis. A client can issue multiple requests, one per interface, to configure interfaces with their specific parameters.

26 = Interface MTU

Specifies the Maximum Transmission Unit (MTU) discovery size for this interface. The minimum MTU value is 68.

27 = All subnets are local

Specifies whether the client assumes that all subnets of the clients internetwork use the same MTU as the local subnet where the client is connected. 1 indicates that all subnets share the same MTU; 0 indicates that the client should assume some subnets may have smaller MTUs.

28 = Broadcast address

Specifies the broadcast address used on the clients subnet.

29 = Perform mask discovery

Specifies whether the client should use Internet Control Message Protocol (ICMP) for subnet mask discovery. 1 indicates the client should perform mask discovery; 0 indicates the client should not.

30 = Mask supplier

Specifies whether the client should respond to subnet mask requests using ICMP. 1 indicates the client should respond; 0 indicates the client should not respond.

31 = Perform router discovery

Specifies whether the client should solicit routers using the router discovery method in RFC 1256. 1 indicates that the client should perform router discovery; 0 indicates that the client should not use it.

32 = Router solicitation address

Specifies the IP address to which the client submits router solicitation requests.

33 = Static route

Specifies a list of IP address pairs that indicate the static routes the client should install in its routing cache. Any multiple routes to the same destination are listed in descending order or priority. The routes are destination/router address pairs. The default route of 0.0.0.0 is an illegal destination for a static route.


Link Layer Parameters per Interface

The following lists link layer parameters per interface. These options affect the operation of the data link layer on a per-interface basis.

34 = Trailer encapsulation

Specifies whether the client should negotiate use of trailers (RFC 983) when using the ARP protocol. 1 indicates the client should attempt to use trailer; 0 indicates the client should not use trailers.

35 = ARP cache timeout

Specifies the timeout in seconds for ARP cache entries.

36 = Ethernet encapsulation

Specifies whether the client should use Ethernet v. 2 (RFC 894) or IEEE 802.3 (RFC 1042) encapsulation if the interface is Ethernet. 1 indicates that the client should use RFC 1042 encapsulation; 0 indicates the client should use RFC 894 encapsulation.


TCP Parameters

The following shows TCP parameters. These options affect the operation of the TCP layer on a per-interface basis.

37 = Default time-to-live

Specifies the default TTL the client should use when sending TCP segments. The minimum value of the octet is 1.

38 = Keepalive interval

Specifies the interval in seconds the client TCP should wait before sending a keepalive message on a TCP connection. A value of 0 indicates that the client should not send keepalive messages on connections unless specifically requested by an application.

39 = Keepalive garbage

Specifies whether the client should send TCP keepalive messages with an octet of garbage data for compatibility with older implementations. 1 indicates that a garbage octet should be sent; 0 indicates that it should not be sent.


Application Layer Parameters per Interface

The following shows application layer parameters. These miscellaneous options are used to configure applications and services.

* = List is specified in order of preference, so that the first in the list is the first to be used.

40 = NIS domain name

Specifies the name of Network Information Service (NIS) domain as an ASCII string.

41 = NIS servers

Specifies a list of IP addresses for NIS servers available to the client.*

42 = NTP servers

Specifies a list of IP addresses for Network Time Protocol (NTP) servers available to the client.*


Vendor-Specific Information

* = List is specified in order of preference, so that the first in the list is the first to be used.

The following options are for vendor-specific information.

You can use Microsoft DHCP Server to set any of the options shown whose code and option name are listed in italic type. If you have third-party DHCP clients, you can set any option listed that is supported by the third-party client software.

43 = Vendor specific info

Binary information used by clients and servers to exchange vendor-specific information. Servers not equipped to interpret the information ignore it. Clients that expect but don't receive the information attempt to operate without it.

NetBIOS over TCP/IP

44 = WINS/NBNS servers

Specifies a list of IP addresses for NetBIOS name servers (NBNS).*

45 = NetBIOS over TCP/IP NBDD

Specifies a list of IP addresses for NetBIOS datagram distribution servers (NBDD).*

46 = WINS/Netbt node type

Allows configurable NetBIOS over TCP/IP clients to be configured as described in RFC 1001/1002, where 1=b-node, 2=p-node, 4=m-node, and 8=h-node. On multihomed computers, the node type is assigned to the entire computer, not to individual adapter cards.

47 = NetBIOS scope ID

Specifies a string that is the NetBIOS over TCP/IP Scope ID for the client, as specified in RFC 1001/1002. On multihomed computers, the scope ID is assigned to the entire computer, not to individual adapter cards.

48 = X Window system font

Specifies a list of IP addresses for X Window font servers available to the client.*

49 = X Window system display

Specifies a list of IP addresses for X Window System Display Manager servers available to the client.*

DHCP Extensions

51 = Lease time

Specifies the time in seconds from address assignment until the client's lease on the address expires. Lease time is specified in the Create Scope or Scope Properties dialog box. It cannot be set directly in a DHCP Options dialog box.

58 = Renewal (T1) time value

Specifies the time in seconds from address assignment until the client enters the renewing state. Renewal time is a function of the lease time option, which is specified in the Create Scope or Scope Properties dialog box. It cannot be set directly in a DHCP Options dialog box.

59 = Rebinding (T2) time value

Specifies the time in seconds from address assignment until the client enters the rebinding state. Rebinding time is a function of the lease time option, which is specified in the Create Scope or Scope Properties dialog box. It cannot be set directly in a DHCP Options dialog box.


Administering DHCP clients
Introduction to Administering DHCP Clients

After you have established the scope and defined the range of available and excluded IP addresses, DHCP-enabled clients can begin using the service for automatic TCP/IP configuration.

You can use DHCP Manager to manage individual client leases, including adding and managing reservations for clients.


Managing Client Leases

The lease for the IP address assigned by a DHCP server has an expiration date, which the client must renew if it is going to continue to use that address. You can view the lease duration and other information for specific DHCP clients and add and change configuration settings for reserved DHCP clients.

Information about active leases in the currently selected scope is shown in the Active Leases dialog box. In addition to information on individual leases and reservations, the Active Leases dialog box also shows the total number of addresses in the scope, the number and percentage of addresses that are currently unavailable because they are active or excluded, and the number and percentage of addresses that are currently available.

Because the count of active leases and excluded addresses is an aggregate, it may not tell you what you want to know about only the active leases. The Active/Excluded count when a scope is deactivated reflects only excluded addresses. To determine the number of active leases and reservations, compare the Active/Excluded count before and after the scope is activated.

Leases are retained in the DHCP server database approximately one day after expiration. This grace period protects a client's lease in case the client and server are in different time zones, the two computers' clocks are not synchronized, or the client computer is off the network when the lease expires. These expired leases are included in the aggregate Active/Excluded count, as well as in the list of active clients in the Active Leases dialog box. They are distinguished by a dimmed icon.

To view client lease information

1.	In the DHCP Servers list in the DHCP Manager window, select the scope for which you want to view or change client information.

2.	From the Scope menu, choose Active Leases.

3.	In the Active Leases dialog box, select the computer whose lease you want to view in the IP Address list, and then choose the Properties button.

If you want to view only clients that use reserved IP addresses, select the Show Reservations Only checkbox.

4.	In the Client Properties dialog box, you can view the unique identifier and other client information, including the lease expiration date.

Note:	You can only edit values or choose the Options button in the Client Properties dialog box for clients with reserved IP addresses. For information about the Options button in this dialog box, see Defining Options for Reservations.

You can delete the lease of any DHCP client in the scope. The main reason for doing so is to remove a lease that conflicts with an IP address exclusion or a client reservation that you want to add. Deleting a lease has the same effect as if the client's lease expired: the next time that client computer starts, it must enter the initialization state and obtain new TCP/IP configuration information from a DHCP server. There is nothing, however, to prevent the client from obtaining a new lease for the same IP address. You must make the address unavailable before the client requests another lease.

Important:

Delete only entries for clients that are no longer using the assigned DHCP lease or that are to be moved immediately to a new address. Deleting an active client could result in duplicate IP addresses on the network, because deleted addresses will be assigned to new active clients. After you delete a client's lease and set a reservation or exclusion, you should always use the ipconfig /release command to force the client to free its IP address.

To delete a client's lease

1.	In the IP Address list, select the client lease you want to cancel, and then choose the Delete button.

If you want to cancel leases for all clients in the scope, choose the Delete All button.

2.	Make a reservation with the IP address, or exclude it from the range.

3.	Force the client with the existing lease to give it up. From the command prompt on the client computer, type the ipconfig/release command.

4.	If you want, give this client a new IP address. From the command prompt on the client computer, type the ipconfig/renew command.


Managing Client Reservations

You can reserve a specific IP address for a client. Typically, you will need to do this if the client uses an IP address that was assigned using another method for TCP/IP configuration.

If multiple DHCP servers are distributing addresses in the same scope, the client reservations on each DHCP server should be identical. Otherwise, the DHCP reserved client will receive different IP addresses, depending on the responding server.

To add a reservation for a client

1.	From the Scope menu, choose Add Reservations.

2.	In the Add Reserved Clients dialog box, type information to identify the first reserved client:

IP Address specifies an address from the reserved address pool. You can specify any reserved, unused IP address. DHCP Manager checks and warns you if a duplicate or non-reserved address is entered.

Unique Identifier specifies the media access control (MAC) address for the client computer's network adapter card. You can determine this address by typing net config wksta at the command prompt on the client computer.

Client Name specifies the computer name for the client. This is used for identification purposes only and does not affect the actual computer name for the client.

Client Comment is any optional text that you enter to describe the client.

3.	Choose the Add button to add the reservation to the DHCP database. You can continue to add reservations without closing this dialog box.

4.	When you have added all reservations, choose the Close button.

If you want to change a reserved IP address for a client, you have to remove the old reserved address, and then add a new reservation. You can change any other information about a reserved client while keeping the reserved IP address.

Reserving an address does not automatically force a client who is currently using the address to move elsewhere. If you are reserving a new address for a client, or an address that is different from the client's current one, you should verify that the address has not already been leased by the DHCP server. If the address is already in use, the client that is using it must release the address by issuing a release request. To make this happen, at the command prompt of the client computer, type the ipconfig/release command. Clients using MS-DOS, and possibly clients using third-party operating systems, will have to restart their computers for the change to take effect. Because the client's current address is now reserved, the client is moved to a different address.

Reserving an address also does not force the client for whom the reservation is made to move to the reserved address. In this case, too, the client must issue a renewal request. At the command prompt of the client computer, type the ipconfig/renew command, and then restart the computer if necessary. The DHCP server will note that the client has a reserved address and will move the client.

After the IP address is reserved in DHCP Manager, restart the client computer to configure it with the new IP address.

To change the reserved IP address

1.	In the Active Leases dialog box, select the reserved IP address, and then choose the Delete button. Then choose the OK button.

2.	From the Scope menu, choose Add Reservations, and then enter information for a new reservation as described earlier in this section.

To change basic information for a reserved client

1.	From the Scope menu, choose Active Leases.

2.	In the IP Address list of the Active Leases dialog box, select the address of the reserved client that you want to change, and then choose the Properties button.

3.	In the Client Properties dialog box, change the unique identifier, client name, or comment, and then choose the OK button.

Note:	You can only change values in the Client Properties dialog box for reserved clients.

You can also view and change the DHCP option types that define configuration parameters for clients with reservations, as described in Defining Options for Reservations.


Remove

Removes the selected DHCP server from the list in the DHCP Manager window.


Add DHCP Server To Known Server List

Use the Add DHCP Server To Known Server List dialog box to specify the name of the DHCP server you want to connect to. This dialog box appears when you choose Add from the Server menu.

DHCP Server

Type the IP address or DNS name for the DHCP server you want to connect to, and then choose OK.

For example, type an address such as 11.1.26.30 or type a DNS name such as corp01.trey.com in this box.

In DHCP Manager, you cannot use the NetBIOS computer name used in Windows NT networking. You must use DNS computer names.


Create Scope and Scope Properties

Use the Create Scope dialog box to create a new scope for a subnet. This dialog box appears when you choose Create from the Scope menu.

Use the Scope Properties dialog box to change the address pool for a scope. This dialog box appears when you choose Properties from the Scope menu.

Choose one of the following buttons for information about this dialog box:

 IP Address Pool Start and End

 Subnet Mask

 Exclusion Range Start and End

 Excluded Addresses

 Lease Duration: Unlimited or Limited To

 Name

 Comment


Lease Duration: Unlimited or Limited To

If you do not want leases to expire for this scope, select Unlimited.

To define when leases should expire for this scope, use the boxes to specify the number of days, hours, and minutes that the lease will last before expiring.


Subnet ID

To identify the subnet associated with this scope, type the first IP address for the related subnet in the Subnet ID box.


Subnet Mask

Type the subnet mask for the related subnet in the Subnet Mask box.

This is 255.0.0.0 for a Class A address, 255.255.0.0 for a Class B address, and 255.255.255.0 for a Class C address.


Primary Server

To define the primary server for this new scope, select a DHCP server name from the Primary Server list. This is the server that will be contacted first when a client in this scope requests DHCP configuration information.


IP Address Pool Start and End

To define the available range of IP addresses for this scope, type the beginning and ending IP addresses for the range in the IP Address Pool Start and End boxes.

The pool includes the addresses entered for the Start and End values.

Note:

You must supply this information to activate the scope on the primary server.


Exclusion Range Start and End

To define excluded addresses within the IP address pool range, use the Exclusion Range controls, as follows:

Type the first IP address that is part of the excluded range in the Start Address box, and type the last number in the End Address box. Then choose the Add button. Continue to define any other excluded ranges in the same way.

To exclude a single IP address, type the number in the Start Address box, and leave the End Address box empty.

The excluded ranges should include all IP addresses that you assigned manually to other DHCP servers, non-DHCP clients, diskless workstations, or RAS clients. These addresses are not available for automatic DHCP configuration.


Excluded Addresses

To remove an IP address from the excluded range, select its number in the Excluded Addresses box, and then choose the Remove button.


Name

In the Name box, type a scope name of up to 128 characters.

This is any name you want to use to describe the subnet. The name can include any combination of letters, numbers, and hyphens.


Comment

Optionally, in the Comment box, type any string to describe the scope, and then choose the OK button.


Sort Order

If you want the Client list to appear in IP address order, select the Sort Leases By IP Address option.

If you want to view the list by DNS name, select Sort Leases By Name.


Active Leases

Use this dialog box to view or change client information for the scope selected in the DHCP Manager window. To display this dialog box, from the Scope menu, choose Active Leases.

Choose one of the following buttons for information about this dialog box:

 Client

 Properties

 Delete

 Reconcile

 Show Reservations Only

 Sort Order

 Options

 Lease Expires


Reconcile

Runs the reconcile program to reconcile the DHCP database with the Registry. When you reconcile the DHCP database with the Registry, a consistency check is done on the DHCP database. All inconsistent IP addresses are listed. Inconsistent IP addresses are addresses that the Registry says are leased but the DHCP database does not reflect this information. The consistency check is performed at the scope level. Therefore, if a server is configured with multiple scopes, reconcile should be run separately for each scope.

Run the reconcile program whenever a DHCP database is restored from a backup copy or after a system crash. It is also a good idea to run the reconcile program periodically to keep the DHCP database clean.


Scope

Shows the name of the scope that was selected in the DHCP Manager window when you chose the Active Clients command.


IP Address

In the IP Address list, select the computer whose lease you want to view or change.


Lease Expires

Shows the date and time set for the current IP address lease to expire for the selected client.


Client Identifier

Shows the unique identifier that specifies the media access control (MAC) address for the client computer's network adapter card.

You can view this address on the client computer by typing net config wksta at the command prompt.


Client Name

Type a new name in the Client Name box to change the identifier for the selected client.

This is used for identification purposes only and does not affect the actual computer name for the client.


Comment

Type any text to describe the selected client.


Show Reservations Only

To view only clients that use reserved IP addresses, check Show Reservations Only.


Options

To change the option types for reserved clients, select a reserved client in the IP Address list, and then choose the Options button to display the DHCP Options: Reservations Settings dialog box.

This button only appears for reserved clients.


Properties

To change the properties for reserved clients, select a reserved client in the IP Address list, and then choose the Properties button to display the Client Properties dialog box.


Delete

To cancel a client's DHCP configuration, in the IP Address list, select the client you want to cancel, and then choose the Delete button.


Add Reserved Clients
Client Properties

Use this dialog box to add, view, or change information for a specified client. To display this dialog box for adding a new reservation, choose the Add Reservations command from the Scope menu. To display this dialog box for viewing information or changing information for a reserved client, select the client name in the Active Clients dialog box, and choose the Properties button.

Choose one of the following buttons for information about this dialog box:

 IP Address

 Unique Identifier

 Client Name

 Client Comment

 Options


IP Address

Type a unique IP address from the reserved address pool.

You can specify any reserved, unused IP address when you are adding a new reservation.

You cannot change the reserved IP address when you are changing information about a reserved client. To change the address for a reserved client, you must delete it in the Active Clients dialog box, and then add a new reservation by choosing Add Reservations from the Scope menu.


Unique Identifier

Type a unique identifier that specifies the media access control (MAC) address for the client computer's network adapter card.

You can determine this address by typing net config wksta at the command prompt on the client computer.


Client Name

Type the computer name for this client.

This is used for identification purposes only and does not affect the actual computer name for the client.


Client Comment

Type any optional text that you want to describe this client.


DHCP Options: Global, Scope, or Reservation

Use this dialog box to assign DHCP options for all scopes on a DHCP server or for a selected scope. To display this dialog box, from the DHCP Options Menu, choose either the Global or Scope command.

You can also use this dialog box to change option types for reservations. To display this dialog box for reserved clients, from the Scope menu, choose Active Client, and in the IP Address list of the Active Leases dialog box, select the reservation address that you want to change. Then choose the Options button. For a new reserved client, choose the Options button in the Add Reserved Clients dialog box.

Choose one of the following buttons for information about this dialog box:

 Options For

 Unused Options

 Active Options

 Value

 Current Value


Value Button

Select the Value button to display or edit the current value for the selected option.


Option Class

Shows the Option type for which these settings apply -- standard or reservations.


Options For

Shows the unique identifier for the DHCP server where these option types are defined.


Active Options

If you want to remove an option type that has been assigned for this class, select its name in the Active Options box, and then choose the Remove button.


Unused Options

In the Unused Options list in the Options Settings dialog box, select the name of the option type that you want to apply, and then choose the Add button to move the name to the Active Options list.

This list shows both predefined options and any custom options that you add. For example, if you want to allow the computers in a selected scope to be able to request specific lease durations, select the option named Address Lease Time in the Unused Options list and choose the Add button.


Current Value

To define the value for an active option, select its name in the Active Options box, and then edit the information in the Current Value box, depending on the data type for the option, as follows:

For an IP address, type the assigned address for the selected option.

For a number, type an appropriate decimal or hexadecimal value for the option.

For a string, type an appropriate ASCII string containing letters and numbers for the option.

For example, to specify the DNS name servers to be used by the clients in a scope, select DNS Server in the Active Options list, and then type a list of IP addresses for DNS servers in the Current Value box.


Add or Edit Option Type

Use this dialog box to add or edit custom DHCP option types.

To display this dialog box, choose Defaults from the DHCP Options Menu , and then select the class you want to change. To add a new option type, choose the New button. To edit an existing custom option type, select the Option Name you want to edit, and then choose the Properties button.

Choose one of the following buttons for information about this dialog box:

 Class

 Name

 Data Type

 Array

 Identifier

 Comment


Class

Describes the Option Class selected in the Default Option Values dialog box.


Name

In the Name box of the Add Option Type dialog box, type a new option name.


Data Type

From the Data Type list, select a data type for this option:

Binary = Value expressed as an array of bytes

Byte = An 8-bit, unsigned integer

Encapsulated = An array of unsigned bytes

IP address = An IP address of the form w.x.y.z

Long = A 32-bit, signed integer

Long integer = A 32-bit, unsigned integer

String = An ASCII text string

Word = A 16-bit, unsigned integer


Array

If this data type represents an array, check the Array box.


Identifier

In the Identifier box, type a unique code number to be associated with this option type.


Comment

Type a description of the option type.


DHCP Options: Default Values

Use this dialog box to change the default value for selected DHCP option types, and to add, delete, or edit custom option types. To display this dialog box, choose Defaults from the DHCP Options Menu.

Choose one of the following buttons for information about this dialog box:

 Option Class

 Option Name

 Default Value

 Comment

 New

 Delete

 Change

 Edit


Option Class

In the Option Class list, select the option class of the option type that you want to view or change.


Option Name

In the Option Name list, select the option type you want to view or change.


Default Value

In this box, type the value to be configured by default for this option type, then choose the OK button.

If the data type for this option requires binary input or is an array, the Edit button appears so that you can display a special dialog box for editing the default value.


Comment

Shows the comment defined in the Add Option Type dialog box for the selected option.


New

To add a new custom option type, choose the New button. Then you can define a name, data type, and identifier in the Add Option Type dialog box.


Delete

To delete an option type, in the Option Name list of the Default Option Values, select the option you want to delete. Then choose the Delete button.


Change

To change the value for an option type selected in the Option Name list of the DHCP Options: Default Values dialog box, choose the Change button. Then choose the related Edit button and complete the Edit dialog box.


Edit and Data Type

The data type displayed is the type that was predefined for this option or that was defined in the Add Option Type dialog box. The Edit button appears if the value for the selected option is an array.

Choose the Edit button to display the IP Array Edit dialog box or the Binary Editor dialog box, depending on the data type of the selected option.


IP Address Array Editor

Use this dialog box to change the default IP address values for a selected option type. To display this dialog box, select an Option Name in the DHCP Options: Default Values dialog box that is an array and that uses IP addresses as its data type. Then choose the Edit button.

Choose one of the following buttons for information about this dialog box:

 Application and Option

 New IP Address

 IP Addresses

 Server Name

 Resolve


Application and Option

Specifies Global, Scope, Reservation as a class type, and specifies the selected option being edited.


New IP Address

Type a new IP address to add to the list, and then choose the Add button to move it to the IP Addresses list.


IP Addresses

Shows the IP addresses that are part of the array that makes up the current default value.

To add a new value to the list, type an address in the New IP Address box, and then choose the Add button.

To remove an address, select it and choose the Remove button.

For most IP address values, the list is specified in order of preference, so that the first in the list is the first to be used. To change the order of an address in the list, select it, and then click the Up or Down Arrow button to move it to a new position.


Server Name

To specify the DHCP server where these IP addresses are defined, type a name or IP address in the box. To resolve a name, choose the Resolve button.


Resolve

To resolve a server name as an IP address, click the Resolve button.


Numeric Value Array Editor

Use this dialog box to change the default values for a selected option type. To display this dialog box, select an Option Name in the Default Option Values dialog box that is an array and that uses numeric values as its data type. Then choose the Edit button.

 Application and Option

 Unit Size

 New Value

 Current Values

 Data Entry Mode


Unit Size

Specifies the data size for the value, in octets.


New Value

Specifies a new value to be added to the array.

Type a value in the New Value box, and then click the Add button to move the value to the Current Values list.


Current Values

Shows the values that are part of the array that makes up the current default value.

To add a new value to the list, type a number in the New Value box, and then choose the Add button.

To remove an address, select it and choose the Remove button.

For most values, the list is specified in order of preference, so that the first in the list is the first to be used. To change the order of a value in the list, select it, and then click the Up or Down Arrow button to move it to a new position.


Data Entry Mode

To specify how you want to enter values, select Decimal or Hexadecimal.


Next Pane

Moves the active working area to the other pane in the DHCP Manager window.


Split

Allows you to move the split bar between the panes in the DHCP Manager window. Drag the mouse, and then click when the bar is in the position you want.


Status Bar

Displays the status bar at the bottom of the DHCP Manager window. The status bar shows information about the currently select command or the current activity, and it also shows whether a selected scope is activated.