Making Decisions for IP Address Management (Task Map)
As part of the DHCP service setup, you determine several aspects of the IP addresses that the server is to manage. If your network needs more than one DHCP server, you can assign responsibility for some IP addresses to each server. You must decide how to divide responsibility for the addresses. The following task map can help you make IP address management decisions.
Number and Ranges of IP Addresses
During the initial server configuration, DHCP Manager allows you to add one block, or range, of IP addresses under DHCP management by specifying the total number of addresses and the first address in the block. DHCP Manager adds a list of contiguous addresses from this information. If you have several blocks of noncontiguous addresses, you can add the others by running DHCP Manager's Address Wizard again, after the initial configuration.
Before you configure your IP addresses, know how many addresses are in the initial block of addresses you want to add and the IP address of the first address in the range.
Client Host Name Generation
The dynamic nature of DHCP means that an IP address is not permanently associated with the host name of the system that is using it. The DHCP management tools can generate a client name to associate with each IP address if you select this option. The client names consist of a prefix, or root name, plus a dash and a number assigned by the server. For example, if the root name is charlie, the client names are charlie-1, charlie-2, charlie-3, and so on.
By default, generated client names begin with the name of the DHCP server that manages them. This strategy is useful in environments that have more than one DHCP server because you can quickly see in the DHCP network tables which clients any given DHCP server manages. However, you can change the root name to any name you choose.
Before you configure your IP addresses, decide if you want the DHCP management tools to generate client names, and if so, what root name to use for the names.
The generated client names can be mapped to IP addresses in /etc/inet/hosts, DNS, or NIS+ if you specify to register host names during DHCP configuration. See Client Host Name Registration for more information.
Default Client Configuration Macros
In Solaris DHCP, a macro is a collection of network configuration options and their assigned values. The DHCP server uses macros to determine what network configuration information to send to a DHCP client.
When you configure the DHCP server, the management tools gather information from system files and directly from you through prompts or command-line options you specify. With this information, the management tools create the following macros:
Clients receive the options contained in the network address macro before the options in the macro that is mapped to IP addresses. This processing order causes the options in the server macro to take precedence over any conflicting options in the network address macro. See Order of Macro Processing for more information about the order in which macros are processed.
Dynamic and Permanent Lease Types
The lease type determines whether the lease policy applies to the IP addresses you are configuring. During initial server configuration, DHCP Manager allows you to select either dynamic or permanent leases for the addresses you are adding. If you configure the DHCP server with the dhcpconfig command, leases are dynamic.
When an IP address has a dynamic lease, the DHCP server can manage the address. The DHCP server can allocate the IP address to a client, extend the lease time, detect when the address is no longer in use, and reclaim the address. When an IP address has a permanent lease, the DHCP server can only allocate the address. The client then owns the address until explicitly releasing the address. When the address is released, the server can assign the address to another client. The address is not subject to the lease policy as long as the address is configured with a permanent lease type.
When you configure a range of IP addresses, the lease type you select applies to all the addresses in the range. To get the most benefit from DHCP, you should use dynamic leases for most of the addresses. You can later modify individual addresses to make them permanent, if necessary. However, the total number of permanent leases should be kept to a minimum.
Reserved IP Addresses and Lease Type
IP addresses can be reserved by manually assigning them to particular clients. A reserved address can be associated with a permanent lease or a dynamic lease. When a reserved address is assigned a permanent lease, the following statements are true:
If a reserved address is assigned a dynamic lease, the address can be allocated only to the client that is bound to the address. However, the client must track lease time and negotiate for a lease extension as if the address were not reserved. This strategy enables you to track when the client is using the address by looking at the network table.
You cannot create reserved addresses for all the IP addresses during the initial configuration. Reserved addresses are intended to be used sparingly for individual addresses.