dhcpd(1Mtcp)

dhcpd -- Dynamic Host Configuration Protocol server

Synopsis

in.dhcpd [ -t timeout ] [ -D debug_level ] [ -b bootpd_port ]

Description

dhcpd implements a Dynamic Host Configuration Protocol (DHCP) server as defined in RFC 1534, RFC 1542, RFC 2131, and RFC 2132.

If there is no IP address specified for a DHCP client in the DHCP configuration file, dhcpd requests an address from the Address Allocation Server (assd) which allocates an address from a pool of addresses consistent with the client's subnet. The Address Allocation Server provides the same service to other daemons which need to assign temporary addresses.

dhcpd can be configured to run from inetd by including the following line in the file /etc/inetd.conf:

   bootps dgram/i udp wait root /usr/sbin/in.dhcpd in.dhcpd

This mode of operation is referred to as ``inetd mode'' and causes dhcpd to be started only when a DHCP request arrives. If it does not receive another packet within fifteen minutes of the last one it received, it will exit to conserve system resources. The -t option controls this timeout (see ``Options'').

When running dhcpd and bootpd on the same host, dhcpd forwards BOOTP packets to the port specified with the -b option. bootpd must be run in "slave mode" (with the -S option). In this mode, bootpd listens on an alternate port. The port ``bootps-alt'' is defined to be 950 in /etc/services, but it can be anything less than 1024.

To run dhcpd and bootpd on the same host from inetd, use the following two lines in the file /etc/inetd.conf:

   bootps dgram/i udp wait root /usr/sbin/in.dhcpd in.dhcpd -b bootps-alt
   bootps-alt dgram udp wait root /usr/sbin/in.bootpd in.bootpd -S

dhcpd can also uses BOOTP gateways (see bootpgw(1Mtcp)) to forward DHCP packets to DHCP clients on another subnet.

It is also possible to run dhcpd in ``standalone mode'' (without inetd) by simply invoking it from a shell like any other regular command. dhcpd automatically detects whether it was invoked from inetd or from a shell and automatically selects the appropriate mode.

To run dhcpd and bootpd on the same host in ``standalone mode'', use the following two commands:

/usr/sbin/in.dhcpd -b port
/usr/sbin/in.bootpd -S -P port

where port is the alternate port where bootpd is listening for BOOTP packets forwarded by dhcpd.

Options

-b bootpd_port: Alternate port assigned to bootpd to listen for packets if both bootpd and dhcpd are running on the same host. bootpd must be running in slave mode (-S).
-D debug_level: Sets the debug_level variable that controls the amount of debugging messages generated. For example, -D 1 will set the debugging level to 1. Recognized values are 0, 1, 2, and 3 or greater. Zero generates no messages and 1 to 3 generate increasing amounts of messages. Specifying an integer greater than 3 has the same result as specifying 3. If dhcpd is running in standalone mode and you specify 3 or greater, messages will be directed to standard error (not to syslog) and dhcpd does not go into the background.
-t timeout: Specifies the timeout value (in minutes) that a dhcpd process will wait for a packet before exiting. If no packets are received for timeout minutes, then the program will exit. A timeout value of zero means ``run forever''. In standalone mode, this option is forced to zero.

dhcpd loads its database of known subnets, clients, classes and DHCP options from the default configuration file, /etc/inet/dhcpd.conf. The DHCP Configuration Manager does not support an alternate configuration database nor does it support an alternate location for this file.

Operation

When dhcpd starts, it reads a configuration database (/etc/inet/dhcpd.conf) that contains known subnets, clients, classes and DHCP options, along with DHCP server parameters. It also records the modification time of the configuration database. dhcpd then listens for any packets sent to the bootps port.

When dhcpd receives a packet, it checks the modification time of the configuration file and reloads the database if necessary. It then constructs the set of parameters corresponding to the client from the DHCP configuration file and responds to the client.

During initialization, dhcpd determines the UDP port numbers to be used by calling getservbyname (see getservent(3N)) which normally reads /etc/services. Two service names (and port numbers) are used:

bootps: DHCP/BOOTP server listening port
bootpc: DHCP/BOOTP client destination port

If the port numbers cannot be determined using getservbyname, then the values default to bootps=67 and bootpc=68.

References

aasd(1Mtcp), bootpd(1Mtcp), dhcpd.conf(4tcp), inetd(1Mtcp)

Standards compliance

RFC 1534, RFC 1542, RFC 2131, RFC 2132