dhclient - Dynamic Host Configuration Protocol (DHCP) Client
dhclient [-dqu] [-c file] [-l file] interface
The dhclient utility provides a means for configuring network interfaces
using DHCP, BOOTP, or if these protocols fail, by statically
assigning an
address.
The name of the network interface that dhclient should attempt to configure
must be specified on the command line.
The options are as follows:
-c file Specify an alternate location, file, for the configuration file.
-d Forces dhclient to always run as a foreground process. By default,
dhclient runs in the foreground until it has
configured
the interface, and then will revert to running in
the background.
-l file Specify an alternate location, file, for the leases
file.
-q Forces dhclient to be less verbose on startup.
-u Forces dhclient to reject leases with unknown options in them.
The default behaviour is to accept such lease offers.
The DHCP protocol allows a host to contact a central server
which maintains
a list of IP addresses which may be assigned on one or
more subnets.
A DHCP client may request an address from this pool,
and then use
it on a temporary basis for communication on the network.
The DHCP protocol
also provides a mechanism whereby a client can learn
important details
about the network to which it is attached, such as the
location of
a default router, the location of a name server, and so on.
On startup, dhclient reads /etc/dhclient.conf for configuration instructions.
It then gets a list of all the network interfaces
that are configured
in the current system. It then attempts to configure each interface
with DHCP.
In order to keep track of leases across system reboots and
server
restarts, dhclient keeps a list of leases it has been assigned in the
/var/db/dhclient.leases.IFNAME file. "IFNAME" represents
the network interface
of the DHCP client (e.g. em0), one for each interface. On startup,
after reading the dhclient.conf(5) file, dhclient reads
the leases
file to refresh its memory about what leases it has been assigned.
Old leases are kept around in case the DHCP server is unavailable when
dhclient is first invoked (generally during the initial system boot process).
In that event, old leases from the
dhclient.leases.IFNAME file
which have not yet expired are tested, and if they are determined to be
valid, they are used until either they expire or the DHCP
server becomes
available.
A mobile host which may sometimes need to access a network
on which no
DHCP server exists may be preloaded with a lease for a fixed
address on
that network. When all attempts to contact a DHCP server
have failed,
dhclient will try to validate the static lease, and if it
succeeds, it
will use that lease until it is restarted.
A mobile host may also travel to some networks on which DHCP
is not
available but BOOTP is. In that case, it may be advantageous to arrange
with the network administrator for an entry on the BOOTP
database, so
that the host can boot quickly on that network rather than
cycling
through the list of old leases.
You must have the Berkeley Packet Filter (BPF) configured in
your kernel.
dhclient requires at least one /dev/bpf* file for each
broadcast network
interface that is attached to your system. See bpf(4) for
more information.
/etc/dhclient.conf DHCP client configuration
file
/var/db/dhclient.leases.IFNAME database of acquired leases
dhclient.conf(5), dhclient.leases(5), dhclient-script(8),
dhcp(8),
dhcpd(8), dhcrelay(8)
dhclient was written by Ted Lemon <[email protected]> and
Elliot Poger <[email protected]>.
The current implementation was reworked by
Henning Brauer <[email protected]>.
OpenBSD 3.6 April 7, 2004
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