Example: Simple DHCP subnet
This example explains how to set up a System i™ model as a Dynamic Host Configuration Protocol (DHCP) server in a simple LAN with four PC clients and a LAN-based printer.
In this example, the System i model acts as a DHCP server for the 10.1.1.0 IP subnet. It is connected to the LAN with its 10.1.1.1 interface.
Figure 1. Simple LAN setup for System i modelWith so few PC clients, administrators can easily type each PC's IP address related information and maintain these information. They only need to visit four PCs in this case. Now imagine that the four PCs become 200 PCs. Setting up each PC's IP information now becomes a time-consuming task that might result in accuracy errors too. DHCP can simplify the process of assigning IP information to clients. If the subnet 10.1.1.0 has hundreds of clients, an administrator only needs to create a single DHCP policy on the system. This policy distributes IP information to each client.
When PC clients send out their DHCP DISCOVER signals, the server responds with the appropriate IP information. In this example, the company also has a LAN-based printer that obtains its IP information from the DHCP server too. But because PC clients depend on the printer's IP address remaining the same, the network administrator should account for that in the DHCP policy. One solution is to assign a constant IP address to the printer. The DHCP server enables you to define a client, like the LAN printer, in the DHCP policy by its MAC address. In the DHCP client definition, you can then assign specific values, such as IP addresses and router addresses, to the intended client.
For a client to communicate with a TCP/IP network, it requires at least an IP address and subnet mask. The clients will get their IP address from the DHCP server, and the DHCP server passes additional configuration information (for example, their subnet mask) using the configuration options.
Planning the DHCP setup for a simple LAN
Table 1. Global configuration options (applies to all clients served by the DHCP server) Object Value Configuration options option 1: Subnet mask 255.255.255.0 option 6: Domain name server 10.1.1.1 option 15: Domain name mycompany.com Subnet addresses not assigned by the system 10.1.1.1 (Domain name server) Is the system performing DNS updates? No Is the system supporting BOOTP clients? No
Table 2. Subnet for PCs Object Value Subnet name SimpleSubnet Addresses to manage 10.1.1.2 - 10.1.1.150 Lease time 24 hours (default) Configuration options
Inherited options
Options from Global configuration
Table 3. Client for printer Object Value Client Name LANPrinter Client Address 10.1.1.5 Configuration options
Inherited options
Options from Global configuration
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Examples: DHCP