dhcptags(4)dhcptags(4)NAMEdhcptags - DHCP and BOOTP server database
DESCRIPTION
Parameters (or options) returned to the client by the DHCP/BOOTP proto‐
col are encoded in the so-called vendor field of the BOOTP packet.
Each option is identified numerically, and also carries a length speci‐
fier. 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 con‐
trary, 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.
FORMAT
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
The currently recognized /etc/join/dhcptags tags are: Maximum reassem‐
bly 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 For‐
ward 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.
FILES
DHCP server database
RELATED INFORMATION
Commands: dhcpparm(8), joind(8).
Files: bootptab(4),
DARPA Internet Request For Comments RFC 1533, RFC 1541, Assigned Num‐
bers delim off
dhcptags(4)
