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DHCLIENT-SCRIPT(8)
Contents
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dhclient-script - DHCP client network configuration script
The DHCP client network configuration script is invoked from
time to time
by dhclient(8). This script is used by the DHCP client to
set each interface's
initial configuration prior to requesting an address, to test
the address once it has been offered, and to set the interface's final
configuration once a lease has been acquired. If no lease
is acquired,
the script is used to test predefined leases, if any, and
also called
once if no valid lease can be identified.
In general, customizations specific to a particular computer
should be
done in the /etc/dhclient.conf file.
When dhclient(8) needs to invoke the client configuration
script, it sets
up a number of environment variables and runs
dhclient-script. In all
cases, $reason is set to the name of the reason why the
script has been
invoked. The following reasons are currently defined: MEDIUM, PREINIT,
ARPCHECK, ARPSEND, BOUND, RENEW, REBIND, REBOOT, EXPIRE,
FAIL and TIMEOUT.
MEDIUM The DHCP client is requesting that an interface's
media type be
set. The interface name is passed in $interface,
and the media
type is passed in $medium.
PREINIT The DHCP client is requesting that an interface be
configured
as required in order to send packets prior to receiving an actual
address. This means configuring the interface with an IP
address of 0.0.0.0 and a broadcast address of
255.255.255.255.
The interface name is passed in $interface, and
the media type
in $medium.
If an IP alias has been declared in
dhclient.conf(5), its address
will be passed in $alias_ip_address, and
that IP alias
should be deleted from the interface, along with
any routes to
it.
ARPSEND The DHCP client is requesting that an address that
has been offered
to it be checked to see if somebody else is
using it, by
sending an ARP request for that address. It's not
clear how to
implement this, so no examples exist yet. The IP
address to
check is passed in $new_ip_address, and the interface name is
passed in $interface.
ARPCHECK The DHCP client wants to know if a response to the
ARP request
sent using ARPSEND has been received. If one has,
the script
should exit with a nonzero status, indicating that
the offered
address has already been requested and should be
declined.
$new_ip_address and $interface are set as with
ARPSEND.
BOUND The DHCP client has done an initial binding to a
new address.
The new IP address is passed in $new_ip_address,
and the interface
name is passed in $interface. The media type
is passed in
$medium. Any options acquired from the server are
passed using
the option name described in dhcp-options(5), except that dashes
(`-') are replaced by underscores (`_') in order to make
valid shell variables, and the variable names
start with new_.
So for example, the new subnet mask would be
passed in
$new_subnet_mask.
When a binding has been completed, a lot of network parameters
are likely to need to be set up. A new
/etc/resolv.conf needs
to be created, using the values of
$new_domain_name and
$new_domain_name_servers (which may list more than
one server,
separated by spaces). A default route should be
set using
$new_routers, and static routes may need to be set
up using
$new_static_routes.
If an IP alias has been declared, it must be set
up here. The
alias IP address will be written as
$alias_ip_address, and other
DHCP options that are set for the alias (e.g.,
subnet mask)
will be passed in variables named as described
previously except
starting with $alias_ instead of $new_. Care
should be
taken that the alias IP address not be used if it
is identical
to the bound IP address ($new_ip_address), since
the other
alias parameters may be incorrect in this case.
RENEW When a binding has been renewed, the script is
called as in
BOUND, except that in addition to all the variables starting
with $new_, there is another set of variables
starting with
$old_. Persistent settings that may have changed
need to be
deleted - for example, if a local route to the
bound address is
being configured, the old local route should be
deleted. If
the default route has changed, the old default
route should be
deleted. If the static routes have changed, the
old ones
should be deleted. Otherwise, processing can be
done as with
BOUND.
REBIND The DHCP client has rebound to a new DHCP server.
This can be
handled as with RENEW, except that if the IP address has
changed, the ARP table should be cleared.
REBOOT The DHCP client has successfully reacquired its
old address after
a reboot. This can be processed as with
BOUND.
EXPIRE The DHCP client has failed to renew its lease or
acquire a new
one, and the lease has expired. The IP address
must be relinquished,
and all related parameters should be
deleted, as in
RENEW and REBIND.
FAIL The DHCP client has been unable to contact any
DHCP servers,
and any leases that have been tested have not
proved to be
valid. The parameters from the last lease tested
should be deconfigured.
This can be handled in the same way
as EXPIRE.
TIMEOUT The DHCP client has been unable to contact any
DHCP servers.
However, an old lease has been identified, and its
parameters
have been passed in as with BOUND. The client
configuration
script should test these parameters and, if it has
reason to
believe they are valid, should exit with a value
of zero. If
not, it should exit with a nonzero value.
The usual way to test a lease is to set up the network as
with REBIND
(since this may be called to test more than one lease) and
then ping the
first router defined in $routers. If a response is received, the lease
must be valid for the network to which the interface is currently connected.
It would be more complete to try to ping all of the
routers
listed in $new_routers, as well as those listed in
$new_static_routes,
but current scripts do not do this.
dhclient.conf(5), dhclient.leases(5), dhclient(8), dhcpd(8),
dhcrelay(8)
The original version of dhclient-script was written for the
Internet
Software Consortium by Ted Lemon <[email protected]> in cooperation with
Vixie Enterprises.
The OpenBSD implementation of dhclient-script was written by
Kenneth R. Westerback <[email protected]>.
If more than one interface is being used, there's no obvious
way to avoid
clashes between server-supplied configuration parameters -
for example,
the stock dhclient-script rewrites /etc/resolv.conf. If
more than one
interface is being configured, /etc/resolv.conf will be repeatedly initialized
to the values provided by one server, and then the
other. Assuming
the information provided by both servers is valid,
this shouldn't
cause any real problems, but it could be confusing.
OpenBSD 3.6 January 1, 1997
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