Planning for Multiple DHCP Servers

If you want to configure more than one DHCP server to manage your IP addresses, consider the following guidelines:

• Divide the pool of IP addresses so that each server is responsible for a range of addresses, and there is no overlap of responsibility.

• Choose NIS+ as your data store, if available. If not, choose text files and specify a shared directory for the absolute path to the data store. The binary files data store cannot be shared.

• Configure each server separately so that address ownership is allocated correctly and so that server-based macros can be automatically created.

• Set up the servers to scan the options and macros in the dhcptab table at specified intervals so that the servers are using the latest information. You can use DHCP Manager to schedule automatic reading of dhcptab as described in Customizing Performance Options for the DHCP Server.

• Be sure all clients can access all DHCP servers so that the servers can support one another. A client that has a valid IP address lease might try to verify its configuration or extend the lease when the server that owns the client's address is not reachable. Another server can respond to the client after the client has attempted to contact the primary server for 20 seconds. If a client requests a specific IP address, and the server that owns the address is not available, one of the other servers handles the request. In this case, the client does not receive the requested address. The client receives an IP address that is owned by the responding DHCP server.

Planning DHCP Configuration of Your Remote Networks

After the initial DHCP configuration, you can place IP addresses in remote networks under DHCP management. However, because the system files are not local to the server, DHCP Manager and dhcpconfig cannot look up information to provide default values, so you must provide the information. Before you try to configure a remote network, be sure you know the following information:

• The remote network's IP address.

• The subnet mask of the remote network. This information can be obtained from the netmasks table in the name service. If the network uses local files, look in /etc/netmasks on a system in the network. If the network uses NIS+, use the command niscat netmasks.org_dir. If the network uses NIS, use the command ypcat -k netmasks.byaddr. Make sure the netmasks table contains all the topology information for all the subnets you want to manage.

• The network type. The clients connect to the network through either a local area network (LAN) connection or a Point-to-Point Protocol (PPP).

• Routing information. Can the clients use router discovery? If not, you must determine the IP address of a router they can use.

• NIS domain and NIS servers, if applicable.

• NIS+ domain and NIS+ servers, if applicable.

See Adding DHCP Networks for the procedure for adding DHCP networks.

Selecting the Tool for Configuring DHCP

After you gather information and plan for DHCP service, you are ready to configure a DHCP server. You can use the DHCP Manager or the command-line utility dhcpconfig to configure a server. DHCP Manager lets you select options and specify data that is then used to create the dhcptab and network tables used by the DHCP server. The dhcpconfig utility requires you to use command-line options to specify data.

DHCP Manager Features

DHCP Manager, a Java™ technology-based GUI tool, provides a DHCP Configuration Wizard. The configuration wizard starts automatically the first time you run DHCP Manager on a system that is not configured as a DHCP server. The DHCP Configuration Wizard provides a series of dialog boxes that prompt you for the essential information required to configure a server: data store format, lease policy, DNS/NIS/NIS+ servers and domains, and router addresses. Some of the information is obtained by the wizard from system files, and you only need to confirm that the information is correct, or to correct information, if necessary.

When you progress through the dialog boxes and approve the information, the DHCP server daemon starts on the server system. You are then prompted to start the Add Addresses Wizard to configure IP addresses for the network. Only the server's network is configured for DHCP initially, and other server options are given default values. You can run DHCP Manager again after the initial configuration is complete to add networks and modify other server options.

See Configuring and Unconfiguring a DHCP Server Using DHCP Manager for more information about the DHCP Configuration Wizard. See About DHCP Manager for more detailed information about DHCP Manager.

dhcpconfig Features

The dhcpconfig utility supports options that enable you to configure and unconfigure a DHCP server, as well as convert to a new data store and import/export data to and from other DHCP servers. When you use the dhcpconfig utility to configure a DHCP server, the utility obtains information from the system files discussed in Updating System Files and Netmask Tables. You cannot view and confirm the information obtained from system files as you can with DHCP Manager. So, it is important that the system files be updated before you run dhcpconfig. You can also use command-line options to override the values dhcpconfig would obtain by default from system files. The dhcpconfig command can be used in scripts. See the dhcpconfig(1M) man page for more information.

Comparison of DHCP Manager and dhcpconfig

The following table summarizes the differences between the two server configuration tools.

Table 13-4 Comparison of DHCP Manager and the dhcpconfig Command

Feature	DHCP Manager	dhcpconfig With Options
Network information that is gathered from system.	Enables you to view the information gathered from system files, and to change it if needed.	You can specify the network information with command-line options.
Speed of configuration.	Speeds the configuration process by omitting prompts for nonessential server options, using default values instead. You can change nonessential options after initial configuration.	Fastest configuration process, but you might need to specify values for many options.

Chapter 14, Configuring the DHCP Service (Tasks) includes procedures you can use to configure your server with either DHCP Manager or the dhcpconfig utility.