ifconfig Commands Used With DHCP Client

The ifconfig command lets you:

• Start the DHCP client- The command ifconfig interface dhcp start initiates the interaction between the DHCP client and DHCP server for the purpose of obtaining an IP address and a new set of configuration options. This might be useful when you change options on the server, such as adding IP addresses or changing the subnet mask, that you want clients to use immediately.

• Request network configuration information only - The command ifconfig interface dhcp inform causes dhcpagent to issue a request for network configuration parameters, with the exception of the IP address. This is useful for situations where the network interface has a valid IP address, but the client system needs updated network options. For example, this might be useful if you do not use DHCP to manage IP addresses, but do use it for configuring hosts on the network.

• Request a lease extension - The command ifconfig interface dhcp extend causes dhcpagent to issue a request to renew the lease. This happens automatically, but you might want to use this 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 dhcp release causes dhcpagent to relinquish the IP address being used by the network interface. This happens automatically when the lease expires. You might want to issue this command if the lease time is long and you need to take down the network interface for an extended period of time or you are removing the system from the network.

• Drop the IP address - The command ifconfig interface dhcp drop causes dhcpagent to take down the network interface without informing the DHCP server that it is doing so. This enables the client to use the same IP address when it reboots.

• Ping the network interface - The command ifconfig interface dhcp ping lets you test to see if the interface is under the control of DHCP.

• View DHCP configuration status of the network interface - The command ifconfig interface dhcp status displays the current state of the DHCP client. The display includes information about whether an IP address has been bound to the client; the number of requests sent, received, and declined; flags indicating whether this is the primary interface; and times indicating when the lease was obtained, expires, and when attempts to renew it will/did start. For example::

  # ifconfig hme0 dhcp status Interface State Sent Recv Declined Flags hme0 BOUND 1 1 0 [PRIMARY] (Began, Expires, Renew) = (07/15/1999 15:27, 07/17/1999 13:31, 07/16/1999 15:24)