dhcptags - DHCP and BOOTP server database
Parameters (or options) returned to the client by the
DHCP/BOOTP protocol are encoded in the so-called vendor
field of the BOOTP packet. Each option is identified
numerically, and also carries a length specifier. The
dhcptags file identifies the type of each option, labels
each with a short mnemonic text string for use in the
dhcpcap database, and provides a description of each for
use in the xjoin program.
Options defined by DHCP are of three general types: The
semantics of which all client and server DHCP implementations
agree upon. These are administered by the Internet
Assigned Numbers Authority (IANA). These options are numbered
from 1 to 127 and 255. Within a specific site all
client and server implementations agree as to the semantics,
but at another site the type and meaning of an
option may be quite different. These options are numbered
from 128 to 254. Each vendor may define 256 options
unique to that vendor. The vendor is identified within a
DHCP packet by the "Vendor Class" option (#60). An option
with a specific numeric identifier belonging to one vendor
will, in general, have a type and semantics different from
those of another vendor. Vendor options are "super-encapsulated"
into the vendor field (#43): within a specific
DHCP packet there may be several instances of option #43.
As well as these, the DHCP implementation defines certain
"pseudo" options, numbered from 512 upward. These are
used by the server to identify items in its database which
either correspond to fixed fields in the BOOTP packet
(such as the "siaddr" field) or which though not options
themselves are used in constructing valid options. For
example, the "home directory" used in constructing the
exact path to a boot image.
In general, the joind server knows little about the semantics
of any of the first three types of options. Its only
duty is to deliver those values to clients that need them.
The responsibility for understanding and using the data
rests with the client. Pseudo-tags, on the contrary, have
a meaning specific to joind, and consequently are not
added to this list. The only useful edit that can be performed
on the pseudo-tags is to change the description or
the mnemonic.
Blank lines and those whose first nonwhitespace character
is '#' are ignored. Data entries are written one per line
and have seven fields. An individual entry cannot be continued
onto another line.
The fields are (in order): The tag number Identifier as
used in bootptab file Grouping in GUI Vendor class Data
type. Choose from the following (case insensitive) list:
A 1-byte value A 2-byte value A 4-byte value A printable
character string An IP address A list of IP addresses A
list of 2-byte values A array of 1-byte values Either true
or false Column grouping in GUI Long name
Tag List [Toc] [Back]
The currently recognized /etc/join/dhcptags tags are: Maximum
reassembly size Arp timeout Broadcast address of network
Boot file Be a router Boot file size (512 octet
blocks) Netbios name servers Netbios datagram distribution
servers Netbios node type Netbios scope Path to join
client binary Cookie servers Class type Dump file DNS
domain name Domain name servers Encapsulate flavor Path of
the extensions file Forward nonlocal datagrams Gateways
(IP rosters) Hardware address Home directory Send host
name Host name Hardware type Client id Impress servers
Host or network IP address IP TTL Keep alive interval Keep
alive octet Log servers LPR servers Lease time Perform
mask discovery Publicly mountable file systems Supply
masks IEN-116 name servers NTP (network time protocol)
servers Policy filters PMTU plateaus Printcap setup SVR4
printer setup PMTU timeout Reply address override Do route
discovery Resource location protocol servers Root path
Solicit routes TFTP server address (used by clients) Boot
server address Subnets are local Subnet mask (host) Static
routes Name service switch Swap server address DHCP T1
DHCP T2 Template host (points to similar host entry) TFTP
root directory (used by secure TFTP server) Time offset
(seconds) Trailers Time servers TCP TTL MTU Vendor magic
cookie selector Netware domain name Netware options X display
managers X font servers NIS domain NIS map servers
NIS+ domain NIS+ map servers
There is also a generic tag, Tn, where n is an RFC 1533
vendor field tag number. Thus it is possible to immediately
take advantage of future extensions to RFC 1533
without being required to modify the DHCP server (joind).
Generic data may be represented as either a stream of hexadecimal
numbers or as a quoted string of ASCII characters.
The length of the generic data is automatically
determined and inserted into the proper field(s) of the
RFC 1533-style BOOTP and DHCP reply.
DHCP server database
Commands: dhcpparm(8), joind(8).
Files: bootptab(4),
DARPA Internet Request For Comments RFC 1533, RFC 1541,
Assigned Numbers delim off
dhcptags(4)
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