dhcpc(1Mtcp)

dhcpc -- DHCP client daemon

Synopsis

in.dhcpc [ -D ] [-d debug_level] [-i interface_name] [-l lease_time] [-r request_address] [-t select_timeout] [-u user_id] [-v vendor_id]

Description

dhcpc (/usr/sbin/in.dhcpc) is the DHCP client program that a system can use to obtain its configuration parameters from a Dynamic Host Configuration Protocol (DHCP) server. It is generally invoked to run as a daemon by an entry in the /etc/inet/config file (see config(4tcp)).

dhcpc understands the following options:

-D: Do not daemonize the DHCP client. This option is intended for debugging purposes.
-d debug_level: Control the amount of debugging messages generated. For example, -d 1 will set the debugging level to 1. Recognized values are 0, 1, 2, 3, and 4. A value of 0 generates no messages and 1 to 4 generate increasing amounts of messages. Specifying an integer greater than 4 has the same result as specifying 4. The default value is 1 which causes dhcpc to report startup messages.
This option overrides the value set for debug in the DHCP client configuration file.
-i interface_name: Specify the name of the network interface on which to broadcast a DHCP discover request (for example, net0). This option is required for systems which have more than one network interface. A received IP address offer will be applied to this interface.
-l lease_time: Specify the lease time in seconds to be requested from the DHCP server.
This option overrides the value set for lease_time in the DHCP client configuration file.
-r request_address: Specify the IP address to be requested from the DHCP server.
This option overrides the value set for request_address in the DHCP client configuration file and the value of CLIENT_IP in /var/adm/dhcpc.info.
-t select_timeout: Specify the time in seconds that the client will wait for an offer from a DHCP server before rebroadcasting a discover message. The default timeout period is 60 seconds.
This option overrides the value set for select_timeout in the DHCP client configuration file.
-u user_id: Specify a set of DHCP user class options to be requested from the DHCP server.
This option overrides the value set for user_id in the DHCP client configuration file.
-v vendor_id: Specify a set of DHCP vendor class options to be requested from the DHCP server.
This option overrides the value set for vendor_id in the DHCP client configuration file.

The format of the DHCP client configuration file, /etc/inet/dhcpc.conf, is described in dhcpc.conf(4tcp).

dhcpc operates as follows:

If a network interface has not been specified using the -i option, dhcpc broadcasts a DHCP discover message on the default (first) network interface. It then waits for an offer from a DHCP server. If the configured selection timeout period expires before it has received an offer, dhcpc rebroadcasts a discover message.
On receiving an offer, dhcpc configures the local host directly with the IP address, broadcast address, and network mask which it has obtained from the DHCP server.
dhcpc writes DHCP options that it obtains from the DHCP server to the file /var/adm/dhcpc.opt with the exception of encapsulated vendor-specific options which are written as raw data to /var/adm/dhcpc.eopt. It writes other received information to /var/adm/dhcpc.info.
dhcpc uses vendor entries in the configuration file to format this data and appends them to /var/adm/dhcpc.opt. The DHCP options in /var/adm/dhcpc.opt are written as shell variable definitions.
dhcpc runs the commands in /etc/inet/dhcpc.conf in the order that they are defined. These commands source the shell variable definitions in /var/adm/dhcpc.opt and use these values selectively to configure the host.
If the -D option was not specified, dhcpc converts itself into a daemon running in the background.

Depending on the entries that are defined in the configuration file, the DHCP options may include the following values:

SUBNET_MASK: The network mask applied to the network interface.
TIME_OFFSET: Specifies the offset of the client's subnet in seconds from Coordinated Universal Time (UTC). A positive offset indicates a location east of the Greenwich meridian, and a negative offset indicates a location west of the Greenwich meridian.
LEASE_TIME: The lease period in seconds of a dynamic IP address that has been assigned to a client.
MESSAGE_TYPE: The type of the last DHCP message that was received. This should normally be 5 for an acknowledgment.
SERVER_IP: The IP address of the DHCP server.
RENEWAL_TIME: The rebind time is the period in seconds after the client obtains its lease at which the DHCP server suggests the client broadcast its first request to renew its lease.
REBIND_TIME: The rebind time is the period in seconds after the client obtains its lease at which the DHCP server suggests the client broadcast its second request to renew its lease.

dhcpc writes other information that it obtains to /var/adm/dhcpc.info:

BOOT_TIME: The date (in seconds since the epoch (00:00 on January 1 1970)) at which the system was booted.
CLIENT_IP: The IP address of the DHCP client.
LEASE_EXPIRY: The date (in seconds since the epoch (00:00 on January 1 1970)) at which the lease of the current IP address will expire.
RELAYA_IP: The IP address of the DHCP (BOOTP) gateway.
SERVER_IP: The IP address of the DHCP server.

When it starts, dhcpc requests the IP address specified by the value of CLIENT_IP in this file unless this is overridden by the value of request_address specified in the configuration file or by the argument to the -r option on the command line.

Client IP address renewal

If the DHCP client acquires a dynamically assigned IP address, it must renew the address before its lease expires. Typically, the client is configured to run as a daemon so that it can renew the lease when 50% of it has run.

If the address is not available for renewal, or the lease expires altogether, the client suspends networking (losing open connections), obtains a new IP address and DHCP options from the server, reinitializes the host's network interface, and then re-runs the configuration commands in /etc/inet/dhcpc.conf with the newly acquired values.

DHCP client daemon control

The DHCP client daemon control program, dcc, allows you to control the operation of dhcpc from the command line. The following operations are available:

dcc dump: Dump the options currently configured for the client to the file /var/tmp/dhcpc.dump. This is equivalent to sending the signal SIGUSR2 to dhcpc.
dcc inform: Send a DHCP request for the options defined in the configuration file /etc/inet/dhcpc.conf. The values in /var/dhcpc/dhcpc.opt are updated and the commands defined in the configuration file are re-run. This is equivalent to sending the signal SIGUSR1 to dhcpc.
dcc reload: Reinitialize the client by running the commands defined in the configuration file /etc/inet/dhcpc.conf. This is equivalent to sending the signal SIGHUP to dhcpc. Note that this does not cause the lease of the IP address to be renewed.
dcc restart: Stop and restart dhcpc.
dcc start: Start dhcpc.
dcc stop: Stop dhcpc. This is equivalent to sending the signal SIGTERM to dhcpc.

Files

/etc/inet/dhcp.opts: list of DHCP global options
/etc/inet/dhcpc.conf: DHCP client configuration parameters
/etc/inet/dhcpd.conf: DHCP server configuration parameters
/etc/inet/dhcpd.pid: DHCP client process ID
/etc/inet/dhcpc/: configuration commands that may be run by dhcpc
/etc/inet/config: contains an entry which can be enabled to invoke dhcpc as a daemon at boot time
/var/adm/dhcpc.eopt: raw vendor-specific DHCP options obtained from the server
/var/adm/dhcpc.opt: DHCP options obtained from the server in a form suitable for shell scripts
/var/adm/dhcpc.info: contains other information used by dhcpc

Usage

The Network Configuration Manager in Configuring LAN connections is used to configure a system as a DHCP client by selecting this option in the basic TCP/IP in Administering TCP/IP and Internet services settings of a LAN interface.

If you need to specify any options to dhcpc, add the options to the line in /etc/inet/config that invokes dhcpc. For example, the following entry specifies the use of interface net1 and a debugging level of 3:

3a:/usr/sbin/in.dhcpc::y:/etc/inet/dhcpc.conf:-i net1 -d 3:

Shut down and reboot the system for the changes to take effect.

References

bootpgw(1Mtcp), config(4tcp), dhcpc.conf(4tcp), dhcpd(1Mtcp), dhcpd.conf(4tcp), ifconfig(1Mtcp), resolv.conf(4tcp), xntpd(1Mtcp)

RFC 1534, RFC 1542, RFC 2131, RFC 2132