dhclient.conf.5

DHCP服务器源码

If for some set of options the client should first use the values
supplied by the server, if any, and then use values you supply, these
values can be defined in the
.B append
statement.   The
.B append
statement can only be used for options which
allow more than one value to be given.   This restriction is not
enforced - if you ignore it, the behaviour will be unpredictable.
.SH LEASE DECLARATIONS
.PP
.I The
.B lease
.I declaration
.PP
 \fBlease {\fR \fIlease-declaration\fR [ ... \fIlease-declaration ] \fB}\fR
.PP
The DHCP client may decide after some period of time (see \fBPROTOCOL
TIMING\fR) that it is not going to succeed in contacting a
server.   At that time, it consults its own database of old leases and
tests each one that has not yet timed out by pinging the listed router
for that lease to see if that lease could work.   It is possible to
define one or more \fIfixed\fR leases in the client configuration file
for networks where there is no DHCP or BOOTP service, so that the
client can still automatically configure its address.   This is done
with the
.B lease
statement.
.PP
NOTE: the lease statement is also used in the dhclient.leases file in
order to record leases that have been received from DHCP servers.
Some of the syntax for leases as described below is only needed in the
dhclient.leases file.   Such syntax is documented here for
completeness.
.PP
A lease statement consists of the lease keyword, followed by a left
curly brace, followed by one or more lease declaration statements,
followed by a right curly brace.   The following lease declarations
are possible:
.PP
 \fBbootp;\fR
.PP
The
.B bootp
statement is used to indicate that the lease was acquired using the
BOOTP protocol rather than the DHCP protocol.   It is never necessary
to specify this in the client configuration file.   The client uses
this syntax in its lease database file.
.PP
 \fBinterface\fR \fB"\fR\fIstring\fR\fB";\fR
.PP
The
.B interface
lease statement is used to indicate the interface on which the lease
is valid.   If set, this lease will only be tried on a particular
interface.   When the client receives a lease from a server, it always
records the interface number on which it received that lease.
If predefined leases are specified in the dhclient.conf file, the
interface should also be specified, although this is not required.
.PP
 \fBfixed-address\fR \fIip-address\fR\fB;\fR
.PP
The
.B fixed-address
statement is used to set the ip address of a particular lease.   This
is required for all lease statements.   The IP address must be
specified as a dotted quad (e.g., 12.34.56.78).
.PP
 \fBfilename "\fR\fIstring\fR\fB";\fR
.PP
The
.B filename
statement specifies the name of the boot filename to use.   This is
not used by the standard client configuration script, but is included
for completeness.
.PP
 \fBserver-name "\fR\fIstring\fR\fB";\fR
.PP
The
.B server-name
statement specifies the name of the boot server name to use.   This is
also not used by the standard client configuration script.
.PP
 \fBoption\fR \fIoption-declaration\fR\fB;\fR
.PP
The
.B option
statement is used to specify the value of an option supplied by the
server, or, in the case of predefined leases declared in
dhclient.conf, the value that the user wishes the client configuration
script to use if the predefined lease is used.
.PP
 \fBscript "\fIscript-name\fB";\fR
.PP
The
.B script
statement is used to specify the pathname of the dhcp client
configuration script.  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.   For
more information, see
.B dhclient-script(8).
.PP
 \fBvendor option space "\fIname\fB";\fR
.PP
The
.B vendor option space
statement is used to specify which option space should be used for
decoding the vendor-encapsulate-options option if one is received.
The \fIdhcp-vendor-identifier\fR can be used to request a specific
class of vendor options from the server.   See
.B dhcp-options(5)
for details.
.PP
 \fBmedium "\fImedia setup\fB";\fR
.PP
The
.B medium
statement can be used on systems where network interfaces cannot
automatically determine the type of network to which they are
connected.  The media setup string is a system-dependent parameter
which is passed to the dhcp client configuration script when
initializing the interface.  On Unix and Unix-like systems, the
argument is passed on the ifconfig command line when configuring the
interface.
.PP
The dhcp client automatically declares this parameter if it uses a
media type (see the
.B media
statement) when configuring the interface in order to obtain a lease.
This statement should be used in predefined leases only if the network
interface requires media type configuration.
.PP
 \fBrenew\fR \fIdate\fB;\fR
.PP
 \fBrebind\fR \fIdate\fB;\fR
.PP
 \fBexpire\fR \fIdate\fB;\fR
.PP
The \fBrenew\fR statement defines the time at which the dhcp client
should begin trying to contact its server to renew a lease that it is
using.   The \fBrebind\fR statement defines the time at which the dhcp
client should begin to try to contact \fIany\fR dhcp server in order
to renew its lease.   The \fBexpire\fR statement defines the time at
which the dhcp client must stop using a lease if it has not been able
to contact a server in order to renew it.
.PP
These declarations are automatically set in leases acquired by the
DHCP client, but must also be configured in predefined leases - a
predefined lease whose expiry time has passed will not be used by the
DHCP client.
.PP
Dates are specified as follows:
.PP
 \fI<weekday> <year>\fB/\fI<month>\fB/\fI<day>
<hour>\fB:\fI<minute>\fB:\fI<second>\fR
.PP
The weekday is present to make it easy for a human to tell when a
lease expires - it's specified as a number from zero to six, with zero
being Sunday.  When declaring a predefined lease, it can always be
specified as zero.  The year is specified with the century, so it
should generally be four digits except for really long leases.  The
month is specified as a number starting with 1 for January.  The day
of the month is likewise specified starting with 1.  The hour is a
number between 0 and 23, the minute a number between 0 and 59, and the
second also a number between 0 and 59.
.SH ALIAS DECLARATIONS
 \fBalias { \fI declarations ... \fB}\fR
.PP
Some DHCP clients running TCP/IP roaming protocols may require that in
addition to the lease they may acquire via DHCP, their interface also
be configured with a predefined IP alias so that they can have a
permanent IP address even while roaming.   The Internet Systems
Consortium DHCP client doesn't support roaming with fixed addresses
directly, but in order to facilitate such experimentation, the dhcp
client can be set up to configure an IP alias using the
.B alias
declaration.
.PP
The alias declaration resembles a lease declaration, except that
options other than the subnet-mask option are ignored by the standard
client configuration script, and expiry times are ignored.  A typical
alias declaration includes an interface declaration, a fixed-address
declaration for the IP alias address, and a subnet-mask option
declaration.   A medium statement should never be included in an alias
declaration.
.SH OTHER DECLARATIONS
 \fBreject \fIip-address\fB;\fR
.PP
The
.B reject
statement causes the DHCP client to reject offers from
servers who use the specified address as a server identifier.   This
can be used to avoid being configured by rogue or misconfigured dhcp
servers, although it should be a last resort - better to track down
the bad DHCP server and fix it.
.PP
 \fBinterface "\fIname\fB" { \fIdeclarations ... \fB }
.PP
A client with more than one network interface may require different
behaviour depending on which interface is being configured.   All
timing parameters and declarations other than lease and alias
declarations can be enclosed in an interface declaration, and those
parameters will then be used only for the interface that matches the
specified name.   Interfaces for which there is no interface
declaration will use the parameters declared outside of any interface
declaration, or the default settings.
.PP
 \fBpseudo "\fIname\fR" "\fIreal-name\fB" { \fIdeclarations ... \fB }
.PP
Under some circumstances it can be useful to declare a pseudo-interface 
and have the DHCP client acquire a configuration for that interface.
Each interface that the DHCP client is supporting normally has a DHCP
client state machine running on it to acquire and maintain its lease.
A pseudo-interface is just another state machine running on the
interface named \fIreal-name\fR, with its own lease and its own
state.   If you use this feature, you must provide a client identifier
for both the pseudo-interface and the actual interface, and the two
identifiers must be different.   You must also provide a separate
client script for the pseudo-interface to do what you want with the IP
address.   For example:
.PP
.nf
	interface "ep0" {
		send dhcp-client-identifier "my-client-ep0";
	}
	pseudo "secondary" "ep0" {
		send dhcp-client-identifier "my-client-ep0-secondary";
		script "/etc/dhclient-secondary";
	}
.fi
.PP
The client script for the pseudo-interface should not configure the
interface up or down - essentially, all it needs to handle are the
states where a lease has been acquired or renewed, and the states
where a lease has expired.   See \fBdhclient-script(8)\fR for more
information.
.PP
 \fBmedia "\fImedia setup\fB"\fI [ \fB, "\fImedia setup\fB", \fI... ]\fB;\fR
.PP
The
.B media
statement defines one or more media configuration parameters which may
be tried while attempting to acquire an IP address.   The dhcp client
will cycle through each media setup string on the list, configuring
the interface using that setup and attempting to boot, and then trying
the next one.   This can be used for network interfaces which aren't
capable of sensing the media type unaided - whichever media type
succeeds in getting a request to the server and hearing the reply is
probably right (no guarantees).
.PP
The media setup is only used for the initial phase of address
acquisition (the DHCPDISCOVER and DHCPOFFER packets).   Once an
address has been acquired, the dhcp client will record it in its lease
database and will record the media type used to acquire the address.
Whenever the client tries to renew the lease, it will use that same
media type.   The lease must expire before the client will go back to
cycling through media types.
.SH SAMPLE
The following configuration file is used on a laptop running NetBSD
1.3.   The laptop has an IP alias of 192.5.5.213, and has one
interface, ep0 (a 3com 3C589C).   Booting intervals have been
shortened somewhat from the default, because the client is known to
spend most of its time on networks with little DHCP activity.   The
laptop does roam to multiple networks.

.nf

timeout 60;
retry 60;
reboot 10;
select-timeout 5;
initial-interval 2;
reject 192.33.137.209;

interface "ep0" {
    send host-name "andare.fugue.com";
    send dhcp-client-identifier 1:0:a0:24:ab:fb:9c;
    send dhcp-lease-time 3600;
    supersede domain-name "fugue.com rc.vix.com home.vix.com";
    prepend domain-name-servers 127.0.0.1;
    request subnet-mask, broadcast-address, time-offset, routers,
	    domain-name, domain-name-servers, host-name;
    require subnet-mask, domain-name-servers;
    script "CLIENTBINDIR/dhclient-script";
    media "media 10baseT/UTP", "media 10base2/BNC";
}

alias {
  interface "ep0";
  fixed-address 192.5.5.213;
  option subnet-mask 255.255.255.255;
}
.fi
This is a very complicated dhclient.conf file - in general, yours
should be much simpler.   In many cases, it's sufficient to just
create an empty dhclient.conf file - the defaults are usually fine.
.SH SEE ALSO
dhcp-options(5), dhclient.leases(5), dhcpd(8), dhcpd.conf(5), RFC2132,
RFC2131.
.SH AUTHOR
.B dhclient(8)
was written by Ted Lemon
under a contract with Vixie Labs.   Funding
for this project was provided by Internet Systems Consortium.
Information about Internet Systems Consortium can be found at
.B http://www.isc.org.