TCP/IP Information
Copyright (C) 1997, 1998 by International Business Machines Corporation

DHCP Server Configuration


Subnet notebook

Use this notebook to create or modify a subnet, its address range and excluded addresses, lease time value for those addresses, and DHCP options served to clients that are assigned addresses from the subnet.

The tabs in this notebook are Subnet Definition, DHCP Options, Miscellaneous, and Client Support.

Fields and settings on the Subnet Definition tab include:

Subnet name
Enter a symbolic name for ease in identifying a subnet. This name appears in the display of the server configuration. If no name is entered, the subnet IP address is used.

Subnet address
Identifies the subnet by IP address in dotted decimal notation (subnet keyword). For example, enter a subnet address of 9.67.48.0 in the field.

Subnet mask

Enter the subnet mask for the subnet in dotted decimal notation or in integer format. The subnet mask defines the entire range of IP addresses in the subnet. For example, enter a subnet mask as a dotted decimal notation of 255.255.240.0 or an integer format of 20. In subnet 9.67.48.0, a mask of 255.255.240.0 implies an address range from 9.67.48.1 to 9.67.63.254. The value 20 is the total number of 1s in a mask expressed in binary as 11111111.11111111.11110000.00000000.

Address range

In dotted-decimal notation, enter the starting and ending values for a range of IP addresses to serve to clients in the subnet.

Addresses excluded from range

Enter IP addresses to exclude from the subnet. To prevent another client from using the fixed address of a router or nameserver, enter the IP address in dotted decimal notation and click Add. For example, exclude hosts that manually define their IP address.

You can enter a single address to exclude or a range of addresses to exclude. To remove an address from the exclusion list, click the address and click Remove. You cannot remove an address that is already excluded from the parent subnet.

Note:

It is recommended that each range of excluded addresses not contain more than 10 addresses. Each excluded address results in a separate Client statement in the configuration file. To exclude larger numbers of addresses, define subnets that do not include the addresses to be excluded. For example, to exclude addresses 50-75 in subnet 9.67.3.0, specify:
subnet 9.67.3.0 255.255.240.0 9.67.3.1-9.67.3.49
subnet 9.67.3.0 255.255.240.0 9.67.3.76-9.67.3.100

Lease
Specifies the duration of time (leaseTimeDefault keyword) a client can use an IP address provided by the DHCP server. The lease time is inherited by clients within the scope of the subnet.

Default lease time
The default value (leaseTimeDefault keyword), which is set in the Server Parameters Notebook.

Enter a lease time
Enables you to specify the lease time.

Permanent lease
Provides an infinite lease time.

Comment
Enter an optional comment about the subnet.


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