1 .\" $OpenBSD: dhclient-script.8,v 1.2 2004/04/09 18:30:15 jmc Exp $
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33 .\" This software has been written for the Internet Software Consortium
34 .\" by Ted Lemon <mellon@fugue.com> in cooperation with Vixie
35 .\" Enterprises. To learn more about the Internet Software Consortium,
36 .\" see ``http://www.isc.org/isc''. To learn more about Vixie
37 .\" Enterprises, see ``http://www.vix.com''.
46 .Nd DHCP client network configuration script
48 The DHCP client network configuration script is invoked from time to
51 This script is used by the DHCP client to set each interface's initial
52 configuration prior to requesting an address, to test the address once it
53 has been offered, and to set the interface's final configuration once a
54 lease has been acquired.
55 If no lease is acquired, the script is used to test predefined leases, if
56 any, and also called once if no valid lease can be identified.
58 .\" No standard client script exists for some operating systems, even though
59 .\" the actual client may work, so a pioneering user may well need to create
60 .\" a new script or modify an existing one.
61 In general, customizations specific to a particular computer should be done
63 .Pa /etc/dhclient.conf
68 needs to invoke the client configuration script, it sets up a number of
69 environment variables and runs
73 is set to the name of the reason why the script has been invoked.
74 The following reasons are currently defined:
75 .Li MEDIUM , PREINIT , ARPCHECK , ARPSEND , BOUND , RENEW , REBIND , REBOOT ,
79 .Bl -tag -width ".Li ARPCHECK"
81 The DHCP client is requesting that an interface's media type be set.
82 The interface name is passed in
84 and the media type is passed in
87 The DHCP client is requesting that an interface be configured as
88 required in order to send packets prior to receiving an actual address.
89 .\" For clients which use the BSD socket library,
90 This means configuring the interface with an IP address of 0.0.0.0
91 and a broadcast address of 255.255.255.255.
92 .\" For other clients, it may be possible to simply configure the interface up
93 .\" without actually giving it an IP address at all.
94 The interface name is passed in
99 If an IP alias has been declared in
100 .Xr dhclient.conf 5 ,
101 its address will be passed in
102 .Va $alias_ip_address ,
103 and that IP alias should be deleted from the interface,
104 along with any routes to it.
106 The DHCP client is requesting that an address that has been offered to
107 it be checked to see if somebody else is using it, by sending an ARP
108 request for that address.
109 It is not clear how to implement this, so no examples exist yet.
110 The IP address to check is passed in
111 .Va $new_ip_address ,
112 and the interface name is passed in
115 The DHCP client wants to know if a response to the ARP request sent
119 If one has, the script should exit with a nonzero status, indicating that
120 the offered address has already been requested and should be declined.
125 variables are set as with
128 The DHCP client has done an initial binding to a new address.
129 The new IP address is passed in
130 .Va $new_ip_address ,
131 and the interface name is passed in
133 The media type is passed in
135 Any options acquired from the server are passed using the option name
140 are replaced by underscores
142 in order to make valid shell variables, and the variable names start with
144 So for example, the new subnet mask would be passed in
145 .Va $new_subnet_mask .
147 When a binding has been completed, a lot of network parameters are
148 likely to need to be set up.
151 needs to be created, using the values of
154 .Va $new_domain_name_servers
155 (which may list more than one server, separated by spaces).
156 A default route should be set using
158 and static routes may need to be set up using
159 .Va $new_static_routes .
161 If an IP alias has been declared, it must be set up here.
162 The alias IP address will be written as
163 .Va $alias_ip_address ,
164 and other DHCP options that are set for the alias (e.g., subnet mask)
165 will be passed in variables named as described previously except starting with
169 Care should be taken that the alias IP address not be used if it is identical
170 to the bound IP address
171 .Pq Va $new_ip_address ,
172 since the other alias parameters may be incorrect in this case.
174 When a binding has been renewed, the script is called as in
176 except that in addition to all the variables starting with
178 there is another set of variables starting with
180 Persistent settings that may have changed need to be deleted - for example,
181 if a local route to the bound address is being configured, the old local
182 route should be deleted.
183 If the default route has changed, the old default route should be deleted.
184 If the static routes have changed, the old ones should be deleted.
185 Otherwise, processing can be done as with
188 The DHCP client has rebound to a new DHCP server.
189 This can be handled as with
191 except that if the IP address has changed,
192 the ARP table should be cleared.
194 The DHCP client has successfully reacquired its old address after a reboot.
195 This can be processed as with
198 The DHCP client has failed to renew its lease or acquire a new one,
199 and the lease has expired.
200 The IP address must be relinquished, and all related parameters should be
206 The DHCP client has been unable to contact any DHCP servers, and any
207 leases that have been tested have not proved to be valid.
208 The parameters from the last lease tested should be deconfigured.
209 This can be handled in the same way as
212 The DHCP client has been unable to contact any DHCP servers.
213 However, an old lease has been identified, and its parameters have
214 been passed in as with
216 The client configuration script should test these parameters and,
217 if it has reason to believe they are valid, should exit with a value of zero.
218 If not, it should exit with a nonzero value.
221 The usual way to test a lease is to set up the network as with
223 (since this may be called to test more than one lease) and then ping
224 the first router defined in
226 If a response is received, the lease must be valid for the network to
227 which the interface is currently connected.
228 It would be more complete to try to ping all of the routers listed in
230 as well as those listed in
231 .Va $new_static_routes ,
232 but current scripts do not do this.
234 .\" Each operating system should generally have its own script file,
235 .\" although the script files for similar operating systems may be similar
236 .\" or even identical.
237 .\" The script files included in the Internet Software Consortium DHCP
238 .\" distribution appear in the distribution tree under client/scripts,
239 .\" and bear the names of the operating systems on which they are intended
242 .Xr dhclient.conf 5 ,
243 .Xr dhclient.leases 5 ,
249 The original version of
251 was written for the Internet Software Consortium by
252 .An Ted Lemon Aq mellon@fugue.com
253 in cooperation with Vixie Enterprises.
260 .An Kenneth R. Westerback Aq krw@openbsd.org .
262 If more than one interface is being used, there is no obvious way to
263 avoid clashes between server-supplied configuration parameters - for
267 .Pa /etc/resolv.conf .
268 If more than one interface is being configured,
270 will be repeatedly initialized to the values provided by one server, and then
272 Assuming the information provided by both servers is valid, this should not
273 cause any real problems, but it could be confusing.