System Administration Guide: IP Services

DHCP Option Information

Historically, DHCP option information has been stored in several places, including the server's dhcptab table, the client's dhcptags file, and internal tables of various programs. In the Solaris 8 release and later releases, the option information is consolidated in the /etc/dhcp/inittab file. See the dhcp_inittab(4) man page for detailed information about the file.

The Oracle Solaris DHCP client uses the DHCP inittab file as a replacement for the dhcptags file. The client uses the file to obtain information about option codes that were received in a DHCP packet. The in.dhcpd, snoop, and dhcpmgr programs on the DHCP server use the inittab file as well.

Determining if Your Site Is Affected

Most sites that use Oracle Solaris DHCP are not affected by the switch to the /etc/dhcp/inittab file. Your site is affected if you meet all of the following criteria:

When you upgrade, the upgrade log notifies you that your dhcptags file had been modified and that you should make changes to the DHCP inittab file.

Differences Between dhcptags and inittab Files

The inittab file contains more information than the dhcptags file. The inittab file also uses a different syntax.

A sample dhcptags entry is as follows:

33 StaticRt - IPList Static_Routes

33 is the numeric code that is passed in the DHCP packet. StaticRt is the option name. IPList indicates that the data type for StaticRt must be a list of IP addresses. Static_Routes is a more descriptive name.

The inittab file consists of one-line records that describe each option. The format is similar to the format that defines symbols in dhcptab. The following table describes the syntax of the inittab file.




Name of the option. The option name must be unique within its option category, and not overlap with other option names in the Standard, Site, and Vendor categories. For example, you cannot have two Site options with the same name, and you should not create a Site option with the same name as a Standard option.


Identifies the namespace in which the option belongs. Must be one of the following: Standard, Site, Vendor, Field, or Internal.


Identifies the option when sent over the network. In most cases, the code uniquely identifies the option, without a category. However, in the case of internal categories such as Field or Internal, a code might be used for other purposes. The code might not be globally unique. The code should be unique within the option's category, and not overlap with codes in the Standard and Site fields.


Describes the data that is associated with this option. Valid types are IP, ASCII, Octet, Boolean, Unumber8, Unumber16, Unumber32, Unumber64, Snumber8, Snumber16, Snumber32, and Snumber64. For numbers, an initial U or S indicates that the number is unsigned or signed. The digits at the end indicate how many bits are in the number. For example, Unumber8 is an unsigned 8-bit number. The type is not case sensitive.


Describes how many units of data make up a whole value for this option.


Describes how many whole values are allowed for this option. 0 indicates an infinite number.


Describes which programs can use this information. Consumers should be set to sdmi, where:









A sample inittab entry is as follows:

StaticRt - Standard, 33, IP, 2, 0, sdmi

This entry describes an option that is named StaticRt. The option is in the Standard category, and is option code 33. The expected data is a potentially infinite number of pairs of IP addresses because the type is IP, the granularity is 2, and the maximum is infinite (0). The consumers of this option are sdmi: snoop, in.dhcpd, dhcpmgr, and dhcpinfo.

Converting dhcptags Entries to inittab Entries

If you previously added entries to your dhcptags file, you must add corresponding entries to the new inittab file if you want to continue using the options you added to your site. The following example shows how a sample dhcptags entry might be expressed in inittab format.

Suppose you had added the following dhcptags entry for fax machines that are connected to the network:

128 FaxMchn - IP Fax_Machine

The code 128 means that the option must be in the Site category. The option name is FaxMchn, and the data type is IP.

The corresponding inittab entry might be:

FaxMchn SITE, 128, IP, 1, 1, sdmi

The granularity of 1 and the maximum of 1 indicate that one IP address is expected for this option.