DHCP Client Configuration File

Purpose

Default configuration information for the Dynamic Host Configuration Protocol (DHCP) client program (dhcpcd).

Description

The dhcpcd configuration file contains entries for logging information, requested options, interfaces to configure, and other items.

Following are the formats for the data in the configuration file.

# Comment line

The # character means that there is a comment from that point to the end of the line.

numLogFiles n

Specifies the number of log files. If 0 is specified, no log file will be maintained and no log message is displayed anywhere. n is the maximum number of log files maintained as the size of the most recent log file reaches its maximum size and a new log file is created.

logFileSize n

Maximum size of a log file. When the size of the most recent log file reaches this value, it is renamed and a new log file is created. n is measured in kilobytes(KB).

logFileName filename

Name and path of the most recent log file. Less recent log files have the number 1 to (n - 1) appended to their names; the larger the number, the older the file.

logItem <option name>

One item that will be logged. Multiple of these lines are allowed. This allows for the specified logging level to be turned on. The following are option names:

SYSERR: System error, at the interface to the platform
OBJERR: Object error, in between objects in the process
PROTERR: Protocol error, between client and server
WARNING: Warning, worth attention from the user
EVENT: Event occurred to the process
ACTION: Action taken by the process
INFO: Information that might be useful
ACNTING: Who was served, and when
TRACE: Code flow, for debugging.

interface <ifName>

The interface to configure DHCP on. This may be the interface that is to be configured. Multiples of these are allowed. There is a special entry, any. This tells the DHCP client to configure the first one it finds and completes successfully. If the any option is used, there should not be any other interface specified. The interface statement may be immediately followed by a pair of curly braces, in which the options requested for this interface can be specified. Options requested within interface curly braces apply only to this interface. See DHCP Server Configuration File for a list of options and formats.

clientid <MAC | HOSTNAME>

Specifies the client id to use in all communication with the server. MAC denotes that the hardware address for the particular interface should be used as the client id. HOSTNAME denotes that the domain host name should be used as the client id. The default is MAC.

sniffer <exec string>

Specifies a string enclosed in quotes, indicating a program to execute to detect hardware failure/recovery for an interface. The dhcp client will look for signal 23(SIGIO) to indicate that the network interface is up and signal 16(SIGURG) to indicate that the network interface is down.

option <code> [<value>] [exec <string>]

Specifies an option requested by this client. Its scope is determined by whether it is inside a set of curly braces for a particular interface, or if it is outside all curly braces. If outside, it applies to all interfaces. code is the option code of the option requested. value is the requested value for that option. This value is passed to the server with the option. The value is not required. The keyword exec denotes a string following which should be executed if this option is returned by the server. This string is expected to be an executable shell script or program. An "%s" may be included in the string. If present, the value returned by the server will be provided in ascii.

vendor

Specifies the special syntax for the specification of the vendor extensions field. It is followed by a set of curly braces. Inside the curly braces, the options and values for the vendor extensions field are specified. The exec string on an option inside the vendor extensions options is not valid. It is ignored.

reject <code>

Specifies that if this option code is returned by the server, this option should be ignored by the client. Its value should not be used.

otherOptions <accept | reject>

Specifies how all other options should be handled by the client. This refers to any options not specifically requested with an "option" statement or rejected with a "reject" statement. The default is that all options are accepted.

updateDNS <string>

A string enclosed in quotes, indicating a program to execute to update the DNS server with the new inverse mapping for the IP address and names served by dhcp. This string should include four %s's to indicate the placement of the following information from the dhcp client:

hostname: Value of option 12. The value returned by the dhcp server is used, if one is supplied. Else, if the client specified a value in this file, the client-requested value is used. If neither the client specified a requested hostname nor the server supplied one, this exec string will not be executed.
domainname: Value of option 15. The value returned by the dhcp server is used, if one is supplied. Else, if the client specified a value in this file, the client-requested value is used. If neither the client specified a requested hostname nor the server supplied one, a null string (" ") will be supplied by dhcp. Therefore, this value is optional.
Ip Address: IP address leased to this client by the server. The string is supplied in dotted notation, for example, 9.2.23.43.
leasetime: Lease time granted by the server. This string is a decimal number representing the number of seconds of the lease.

These values are output by dhcp in this order:

hostname domainname Ip Address leasetime

A script /usr/sbin/dhcpaction has been provided with this function, as well as actions to help NIM interact with DHCP clients. Run the script as follows:

/usr/sbin/dhcpaction hostname domainname ipaddress
leasetime < A | PTR | BOTH | NONE > NONIM

The first four parameters are what will be used to update the DNS server. The fifth parameter tells dhcpaction to update the A record, the PTR record, or both, or none. The options are A, PTR, BOTH, NONE. The sixth parameter is used to tell servers that NIM is being used, and processing needs to be done when a client changes address. The options for this are NIM and NONIM. On clients, this must be set to NONIM.

An example follows:

updateDNS "/usr/sbin/dhcpaction %s %s %s %s %s PTR
NONIM 2>&1 >>/tmp/updns.out"

initTimeout <timeout>

Specifies the timeout value in minutes. If the dhcp client fails to configure an address for an interface within this timeout value, it stops making further attempts. This entry applies to systems running AIX® 5.2 and subsequent releases.

This file is part of TCP/IP in Network Support Facilities in Base Operating System (BOS) Runtime.

Example

This example tells the dhcpcd daemon to use log files of a maximum of 100Kb in size and at most four of them.

The base name for the log files is /usr/tmp/dhcpsd.log. The user also would like to only log four of the nine possible log entry types. The user also specified a string to use for updating the Dynamic Domain Name Server. The user also specified that the clientid to the server should be based on the mac-address of the interface adapter that is trying to be configured. The user also specified that all options should be accepted and instantiated (otheroptions accept), except for option 9 (reject 9).

The options the user specified were the domain (option 15), but since this option is global to the interface keywords, it applies to both interfaces.

Inside each interface, the hostname is specified with option 12.

numLogFiles     4
logFileSize     100
logFileName     /usr/tmp/dhcpsd.log
logItem         SYSERR
logItem         OBJERR
logItem         PROTERR
logItem         TRACE

updateDNS "nsupdate -h%s -d%s -i% %s"

clientid MAC
otheroptions accept
reject 9

option 15 "austin.ibm.com"

interface en0
{
        option 12 "e-chisos"
}

interface tr0
{
        option 12 "t-chisos"
}