DHCP Client Administration

The DHCP client software does not require administration under normal system operation. The dhcpagent daemon automatically starts when the system boots, renegotiates leases, and stops when the system shuts down. You should not manually start and stop the dhcpagent daemon directly. Instead, as superuser on the client system, you can use the ifconfig command to affect dhcpagent's management of the network interface, if necessary.

ifconfig Command Options Used With the DHCP Client

This section summarizes the command options, which are documented in the ifconfig(1M) man page. The only difference between the DHCPv4 and the DHCPv6 versions of these commands is the “inet6” keyword. Include the “inet6” keyword for DHCPv6, but leave it out when running DHCPv4.

The ifconfig command enables you to do the following:

• Start the DHCP client – The command ifconfig interface [inet6] dhcp start initiates the interaction between dhcpagent and the DHCP server to obtain an IP address and a new set of configuration options. This command is useful when you change information that you want a client to use immediately, such as when you add IP addresses or change the subnet mask.

• Request network configuration information only – The command ifconfig interface [inet6] dhcp inform causes dhcpagent to issue a request for network configuration parameters, with the exception of the IP address. This command is useful when the network interface has a static IP address, but the client system needs updated network options. For example, this command is useful if you do not use DHCP to manage IP addresses, but you do use it to configure hosts on the network.

• Request a lease extension – The command ifconfig interface [inet6] dhcp extendipadm refresh-addr dhcp-addrobj causes dhcpagent to issue a request to renew the lease. The client does automatically request to renew leases. However, you might want to use this command if you change the lease time and want clients to use the new lease time immediately, rather than waiting for the next attempt at lease renewal.

• Release the IP address – The command ifconfig interface [inet6] dhcp release causes dhcpagent to relinquish the IP address used by the network interface. Release of the IP address happens automatically when the lease expires. You might want to issue this command with a laptop, for example, when leaving a network and planning to start the system on a new network. See also the /etc/default/dhcpagent configuration file RELEASE_ON_SIGTERM property.

• Drop the IP address – The command ifconfig interface [inet6] dhcp drop causes dhcpagent to take down the network interface without informing the DHCP server and cache the lease in the file system. This command enables the client to use the same IP address when it reboots.

• Ping the network interface – The command ifconfig interface [inet6] dhcp ping lets you determine if the interface is under the control of DHCP.

• View the DHCP configuration status of the network interface – The command ifconfig interface [inet6] dhcp status displays the current state of the DHCP client. The display indicates the following items:

  • If an IP address has been bound to the client

  • The number of requests sent, received, and declined

  • If this interface is the primary interface

  • Times when the lease was obtained, when it expires, and when renewal attempts are scheduled to begin

  For example:

  # ifconfig hme0 dhcp status
  Interface  State         Sent  Recv  Declined  Flags 
  hme0       BOUND            1     1         0   [PRIMARY]  
  (Began,Expires,Renew)=(08/16/2005 15:27, 08/18/2005 13:31, 08/17/2005 15:24)

  # ifconfig hme0 inet6 dhcp status
  Interface  State         Sent  Recv  Declined  Flags 
  hme0       BOUND            1     0         0   [PRIMARY]  
  (Began,Expires,Renew)=(11/22/2006 20:39, 11/22/2006 20:41, 11/22/2006 20:40)

Setting DHCP Client Configuration Parameters

The /etc/default/dhcpagent file on the client system contains tunable parameters for the dhcpagent. You can use a text editor to change several parameters that affect client operation. The /etc/default/dhcpagent file is well documented, so for more information, you should refer to the file as well as to the dhcpagent(1M) man page.

The /etc/dhcp.interface file is another location in which parameters affecting the DHCP client are set. Parameters set in this file are used by system startup scripts with the ifconfig command. This, however, affects only DHCPv4. There is no DHCPv6 equivalent.

By default, the DHCP client is configured as follows:

For DHCPv4

• The client system does not require a particular host name.

  If you want a client to request a specific host name, see DHCPv4 Client Host Names.

• Default requests for the client are given in /etc/default/dhcpagent, and includes DNS Server, DNS domain, and broadcast address.

  The DHCP client's parameter file can be set up to request more options in the PARAM_REQUEST_LIST keyword in the /etc/default/dhcpagent file. The DHCP server can be configured to provide options that were not specifically requested. See About DHCP Macros and Working With DHCP Macros (Task Map) for information about using DHCP server macros to send information to clients.

For DHCPv4 and DHCPv6

• The client system uses DHCP on one physical network interface.

  If you want to use DHCP on more than one physical network interface, see DHCP Client Systems With Multiple Network Interfaces.

• The client is not automatically configured as a name service client if the DHCP client was configured after the Oracle Solaris installation.

  See DHCP Client Systems and Name Services for information about using name services with DHCP clients.