Server Databases

The DHCP/BOOTP server uses two types of databases: the dhcptab database and the dhcp_network databases (see dhcp_network(4).

The dhcptab database contains macros defined using a termcap-like syntax. This syntax permits network administrators to define groups of DHCP configuration parameters to be returned to clients. There are currently 77 predefined parameters.

A DHCP/BOOTP server returns hostname, network broadcast address, network subnet mask, or IP maximum transfer unit (MTU), if this information is requested by a client attached to the same network as the server. This information does not have to be explicitly configured in the dhcptab. The dhtadm command manages the dhcptab service configuration table.

If there are two servers sharing a distributed dhcptab table, the administrator can configure the DHCP parameters in the table so the servers back each other up, provided that they are in the same NIS+ domain. However, each should be primarily responsible for a different range of IP addresses. Each network might require a BOOTP relay agent as well, so its clients can reach the server on the other network.

The dhcp_network databases contain client identifier-to-IP address mappings. These databases are named after the network they support. There is one dhcp_network database for each network that offers DHCP/BOOTP services. The dhcp_network databases are located dynamically by the server and consulted during runtime. A client request received from a network for which no dhcp_network database exists is ignored.

The dhcp_network database maps a DHCP client's client identifier to an IP address and the configuration parameter associated with that IP address. This database is located by the DHCP server at runtime by generating a dhcp_network database name by using the IP network address and subnet mask for the network where the DHCP request originated. For example, a dhcp_network database that supports the 10.0.0.0 network would be called 10_0_0_0. The dhcp_network databases can exist as NIS+ tables or ASCII files. Use the pntadm command to manage the dhcp_network databases.

The in.dhcpd daemon has two run modes, DHCP server (with optional BOOTP compatibility mode) and BOOTP relay agent mode (see in.dhcpd(1M).