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DHCP(7) Miscellaneous Information Manual DHCP(7) NAME DHCP, dhcp - Dynamic Host Configuration Protocol (DHCP) introductory information DESCRIPTION The Dynamic Host Configuration Protocol (DHCP) enables the automatic assignment of IP addresses to clients on networks from a pool of ad- dresses. The IP address assignment and configuration occurs automati- cally whenever appropriately client systems (workstations and portable computers) attach to a network. The DIGITAL UNIX implementation of DHCP is based on the JOIN product by Competitive Automation. JOIN is a trademark of Competitive Automation. Using DHCP has the following advantages: Automates IP address adminis- tration Provides central configuration of network computers Eliminates duplicate IP addresses Supports older style BOOTP (on clients only) The DHCP Environment DHCP is based on the client-server model, in which client systems re- quest resources from other systems called servers. A server is any host system or process that provides a network service. A client is any host system or process that uses services from a server. A single host, or server, can provide more than one service. Servers are passive; they do not call clients, they wait for clients to call them. The client always initiates the DHCP request. The server answers the request, subject to its own configuration rules. The DHCP Software The DHCP software contains the following components: Daemon programs that handle communications between server (joind) and client (joinc). A graphical user interface program (xjoin) that sets up the DHCP dy- namic databases. Configuration files that contain information needed to start the DHCP daemons. Administrative commands, such as programs that enable you to configure and maintain DHCP. The following sections describe these components. The DHCP Daemons On the DIGITAL UNIX system, the DHCP daemons (joind and joinc) reside in the /usr/sbin directory. The following sections describe the daemons and their tasks. The joind Daemon The joind DHCP server daemon performs the following tasks: Reads the /etc/bootptab configuration file and /etc/join/server.pcy policy file. Listens for client hosts requesting BOOTP or DHCP information. If a client is on a network administered by the server, joind responds with an Internet address and other information that allows the client to boot and configure its TCP/IP stack. The bootpd daemon is no longer needed on the server because the joind daemon supports both BOOTP and DHCP requests. The joinc Daemon The joinc DHCP client daemon performs the following tasks: Reads the /etc/join/client.pcy policy file. If requested to configure an inter- face, joinc starts the DHCP protocol handshake. Sends a request to the broadcast address for the network or subnet. Receives configuration information, configures and brings up the interface, and then sleeps in the background until it needs to renew the lease. If it cannot renew the lease, joinc brings down the interface. xjoin Graphical User Interface Program The xjoin graphical user interface program resides in the /usr/bin/X11 directory, and enables you to configure the DHCP server and set up the DHCP dynamic databases. DHCP Configuration Files The /etc/bootptab file contains entries for both DHCP and BOOTP clients. You add, delete, and modify entries in this file by using the xjoin program. The entries are then used by the joind server daemon to configure the DHCP and BOOTP clients. The following table lists additional DHCP configuration files that re- side in the /etc/join directory: tab(@); lfHB lfHB lfCW l. _ Command@Function _ client.pcy@Governs the behavior of a DHCP client. join.ipaddresses@Specifies acceptable IP address formats. namepool@Specifies names for dynamic name assignment. nets@Specifies the networks to administer to joind. server.pcy@Governs the behavior of a DHCP server. _ The client.pcy and server.pcy files contain information about remote systems contacted by DHCP, the devices used to contact these systems, the times to contact the systems, and the level of access that remote systems can have to the local system. You must edit the client.pcy file by hand. You modify the server.pcy file by using the xjoin pro- gram. Configuring these files is optional. The other files are configured using the xjoin program. Administrative Commands The following table lists the DHCP administrative commands and their functions. These commands are used by joind, joinc, or xjoin, and not typically run by administrators. tab(@); lfHB lfHB lfCW l. _ Command@Function _ dhcpconf@Controls invocation of DHCP on the client. dhcpparm@Prints client DHCP parameters. probenis@Checks for the existence of a NIS server on the network. shleases@Displays a client's IP address leases. showdbs@Displays the contents of the server's dynamic database. showdhc@Displays a client's configuration files. _ RESTRICTIONS A cluster member should never be a DHCP client. It should always use static addressing. If a cluster is to support a DHCP server, there can only be one DHCP server for all the cluster members using a common database with failover. RELATED INFORMATION Commands: dhcpconf(8), dhcpparm(8), probenis(8), shleases(8), showdbs(8), showdhc(8). Daemons: joinc(8), joind(8). Files: client.pcy(4), dhcptags(4), join.ipaddresses(4). namepool(4), nets(4), server.pcy(4). Technical Overview, Network Administration delim off DHCP(7)