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System Administration Guide: IP Services

Mapping Your Network Topology

If you have not already done so, you should map the physical structure or layout of your network. Indicate the location of routers and clients, and the location of servers that provide network services. This map 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 “Planning Your TCP/IP Network” in System Administration Guide, Volume 3 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 macros. 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 discover:

Network Topology to Avoid

DHCP does not work well in network environments where more than one IP network shares 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. This makes 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 reconfiguration include: