sbin/dhclient/dhclient-script.8

.\" $OpenBSD: src/sbin/dhclient/dhclient-script.8,v 1.6 2011/04/04 11:43:20 krw Exp $
.\"
.\" Copyright (c) 1997 The Internet Software Consortium.
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.\" This software has been written for the Internet Software Consortium
.\" by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
.\" Enterprises.  To learn more about the Internet Software Consortium,
.\" see ``http://www.isc.org/isc''.  To learn more about Vixie
.\" Enterprises, see ``http://www.vix.com''.
.\"
.Dd August 4, 2012
.Dt DHCLIENT-SCRIPT 8
.Os
.Sh NAME
.Nm dhclient-script
.Nd DHCP client network configuration script
.Sh DESCRIPTION
The DHCP client network configuration script is invoked from time to
time by
.Xr dhclient 8 .
.Pp
.\" No standard client script exists for some operating systems, even though
.\" the actual client may work, so a pioneering user may well need to create
.\" a new script or modify an existing one.
In general, customizations specific to a particular computer should be done
in the
.Pa /etc/dhclient.conf
file.
.Sh OPERATION
When
.Xr dhclient 8
needs to invoke the client configuration script, it sets up a number of
environment variables and runs
.Nm .
In all cases,
.Va $reason
is set to the name of the reason why the script has been invoked.
The following reasons are currently defined:
BOUND, RENEW, REBIND, REBOOT, EXPIRE, FAIL and TIMEOUT.
.Bl -tag -width "ARPCHECK"
.It BOUND
The DHCP client has done an initial binding to a new address.
The new IP address is passed in
.Va $new_ip_address ,
and the interface name is passed in
.Va $interface .
Any options acquired from the server are passed using the option name
described in
.Xr dhcp-options 5 ,
except that dashes
.Pq Sq -
are replaced by underscores
.Pq Sq _
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
.Va $new_subnet_mask .
.Pp
When a binding has been completed, a lot of network parameters are
likely to need to be set up.
A new
.Pa /etc/resolv.conf
needs to be created, using the values of
.Va $new_domain_name
and
.Va $new_domain_name_servers
(which may list more than one server, separated by spaces).
A default route should be set using
.Va $new_routers ,
and static routes may need to be set up using
.Va $new_static_routes .
.Pp
Note: since
.Nm
effectively overwrites
.Pa /etc/resolv.conf ,
any information contained therein is lost.
If options must be passed to the resolver,
they may be contained in
.Pa /etc/resolv.conf.tail ,
which is appended to the generated
.Pa /etc/resolv.conf
by
.Nm .
.\"See
.\".Xr resolv.conf.tail 5
.\"for further information.
.Pp
.It 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.
.It 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.
.It REBOOT
The DHCP client has successfully reacquired its old address after a reboot.
This can be processed as with BOUND.
.It 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.
.It 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.
.It 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.
.El
.Pp
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
.Va $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
.Va $new_routers ,
as well as those listed in
.Va $new_static_routes ,
but current scripts do not do this.
.\" .Sh FILES
.\" Each operating system should generally have its own script file,
.\" although the script files for similar operating systems may be similar
.\" or even identical.
.\" The script files included in the Internet Software Consortium DHCP
.\" distribution appear in the distribution tree under client/scripts,
.\" and bear the names of the operating systems on which they are intended
.\" to work.
.Sh SEE ALSO
.Xr dhclient.conf 5 ,
.Xr dhclient.leases 5 ,
.\".Xr resolv.conf.tail 5 ,
.Xr dhclient 8 ,
.Xr dhcpd 8 Pq Pa pkgsrc/net/isc-dhcpd4 ,
.Xr dhcrelay 8 Pq Pa pkgsrc/net/isc-dhcrelay4
.Sh AUTHORS
.An -nosplit
The original version of
.Nm
was written for the Internet Software Consortium by
.An Ted Lemon Aq mellon@fugue.com
in cooperation with Vixie Enterprises.
.Pp
The
.Ox
implementation of
.Nm
was written by
.An Kenneth R. Westerback Aq krw@openbsd.org .
.Sh BUGS
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
.Pa /etc/resolv.conf .
If more than one interface is being configured,
.Pa /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.