Mapping Your Network Topology

If you have not already done so, you should map out the physical structure or layout of your network, indicating the location of routers and clients, and the location of servers providing network services. This mapping of your network topology can help you determine which server to use for DHCP services, and what configuration information the DHCP server can provide to clients.

See Chapter 5, Planning Your TCP/IP Network for more information about planning your network.

The DHCP configuration process can look up some network information from the server's system and network files. "Updating System Files and Netmask Tables" discusses these files. However, you might want to give clients other service information, which you must enter into the server's databases. As you examine your network topology, record the IP addresses of any servers you want your clients to know about. The following are some examples of network services you may have on your network that the DHCP configuration does not find out about:

• Time server

• Log server

• Print server

• Install server

• Boot server

• Swap server

• X window font server

• TFTP server

Network Topology to Avoid

DHCP does not work well in network environments where more than one IP network is sharing the same network hardware media, either through the use of multiple network hardware interfaces or multiple logical interfaces. When multiple IP networks run across the same physical LAN, a DHCP client's request arrives on all network hardware interfaces, making the client appear to be attached to all of the IP networks simultaneously.

DHCP must be able to determine the address of a client's network in order to assign an appropriate IP address to the client. If more than one network is present on the hardware media, the server cannot determine the client's network, and cannot assign an IP address.

You can use DHCP on one of the networks, but not more than one. If this does not suit your needs, you must reconfigure the networks. Suggestions for reconfiguring include:

• Use variable length subnet masks (VLSM) to make better use of the IP address space you have, so you do not need to run multiple LANs on the same physical network. See RFC-1519 for more information on VLSM and Classless Inter-Domain Routing (CDIR).

• Configure the ports on your switches to assign devices to different physical LANs. This preserves the mapping of one LAN to one IP network required for Solaris DHCP. See the documentation for the switch for information about port configuration.

Determining the Number of DHCP Servers

The data store method you use has a direct effect on the number of servers you must have to support your DHCP clients. If you use the local files method one server can support a maximum of 10,000 clients. If you use NIS+ one server can support a maximum of 40,000 clients.

The section "Choosing the Data Store" discusses data store locations.