hostname:tg=value. . . :tg=value. . . :tg=value. . . .
where
hostname
is the actual name of a bootp client and
tg
is a two-character tag symbol. Most tags must be followed by an equals-sign
and a value as above. Some may also appear in a boolean form with no
value (i.e.
:tg:).
The currently recognized tags are:
bf Bootfile
bs Bootfile size in 512-octet blocks
cs Cookie server address list
ds Domain name server address list
gw Gateway address list
ha Host hardware address
hd Bootfile home directory
hn Send client's hostname to client
ht Host hardware type (see Assigned Numbers RFC)
im Impress server address list
ip Host IP address
lg Log server address list
lp LPR server address list
ns IEN-116 name server address list
rl Resource location protocol server address list
sa TFTP server address client should use
sm Host subnet mask
tc Table continuation (points to similar "template" host entry)
td TFTP root directory used by "secure" TFTP servers
to Time offset in seconds from UTC
ts Time server address list
vm Vendor magic cookie selector
md Merit dump file name
dn Client domain name
ss Swap server address
rp Root path name
There is also a generic tag, Tn, where n is an RFC1084 vendor field tag number. Thus it is possible to immediately take advantage of future extensions to RFC1084 without being forced to modify bootpd first. 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 RFC1084-style bootp reply.
The following tags take a whitespace-separated list of IP addresses: cs, ds, gw, im, lg, lp, ns, rl, and ts. The ip, sa, ss, and sm tags each take a single IP address. All IP addresses are specified in standard Internet "dot" notation and may use decimal, octal, or hexadecimal numbers (octal numbers begin with 0, hexadecimal numbers begin with '0x' or '0X').
The ht tag specifies the hardware type code as either an unsigned decimal, octal, or hexadecimal integer or one of the following symbolic names: ethernet or ether for 10Mb Ethernet, ethernet3 or ether3 for 3Mb experimental Ethernet, ieee802, tr, or token-ring for IEEE 802 networks, pronet for Proteon ProNET Token Ring, or chaos, arcnet, or ax.25 for Chaos, ARCNET, and AX.25 Amateur Radio networks, respectively. The ha tag takes a hardware address which must be specified in hexadecimal; optional periods and/or a leading '0x' may be included for readability. The ha tag must be preceded by the ht tag (either explicitly or implicitly; see tc below).
The hostname, home directory, and bootfile are ASCII strings which may be optionally surrounded by double quotes ("). The client's request and the values of the hd and bf symbols determine how the server fills in the bootfile field of the bootp reply packet.
If the client specifies an absolute pathname and that file exists on the server machine, that pathname is returned in the reply packet. If the file cannot be found, the request is discarded; no reply is sent. If the client specifies a relative pathname, a full pathname is formed by prepending the value of the hd tag and testing for existence of the file. If the hd tag is not supplied in the configuration file or if the resulting boot file cannot be found, then the request is discarded.
Clients which specify null boot files will always elicit a reply from the server. The exact reply will again depend upon the hd and bf tags. If the bf tag gives an absolute pathname and the file exists, that pathname is returned in the reply packet. Otherwise, if the hd and bf tags together specify an accessible file, that filename is returned in the reply. If a complete filename cannot be determined or the file does not exist, the reply will contain a zeroed-out bootfile field.
In all these cases, existence of the file means that, in addition to actually being present, the file must have its public read access bit set, since this is required by tftpd(8) to permit the file transfer. Also, all filenames are first tried as filename.hostname and then simply as filename, thus providing for individual per-host bootfiles.
Some newer versions of tftpd provide a security feature to change their root directory using the chroot(2) system call. The td tag may be used to inform bootpd of this special root directory used by tftpd. The hd tag is actually relative to the root directory specified by the td tag. For example, if the real absolute path to your BOOTP client bootfile is /tftpboot/bootfiles/bootimage, and tftpd uses /tftpboot as its "secure" directory, then specify the following in bootptab:
:td=/tftpboot:hd=/bootfiles:bf=bootimage:
If your bootfiles are located directly in /tftpboot, use:
:td=/tftpboot:hd=/:bf=bootimage:
The sa tag may be used to specify the IP address of the particular TFTP server you wish the client to use. In the absence of this tag, bootpd will tell the client to perform TFTP to the same machine bootpd is running on.
The time offset to may be either a signed decimal integer specifying the client's time zone offset in seconds from UTC, or the keyword auto which uses the server's time zone offset. Specifying the to symbol as a boolean has the same effect as specifying auto as its value.
The bootfile size bs may be either a decimal, octal, or hexadecimal integer specifying the size of the bootfile in 512-octet blocks, or the keyword auto which causes the server to automatically calculate the bootfile size at each request. As with the time offset, specifying the bs symbol as a boolean has the same effect as specifying auto as its value.
The vendor magic cookie selector (the vm tag) may take one of the following keywords: auto (indicating that vendor information is determined by the client's request), rfc1048 or rfc1084 (which always forces an RFC1084-style reply), or cmu (which always forces a CMU-style reply).
The hn tag is strictly a boolean tag; it does not take the usual equals-sign and value. It's presence indicates that the hostname should be sent to RFC1084 clients. Bootpd attempts to send the entire hostname as it is specified in the configuration file; if this will not fit into the reply packet, the name is shortened to just the host field (up to the first period, if present) and then tried. In no case is an arbitrarily-truncated hostname sent (if nothing reasonable will fit, nothing is sent).
Often, many host entries share common values for certain tags (such as name servers, etc.). Rather than repeatedly specifying these tags, a full specification can be listed for one host entry and shared by others via the tc (table continuation) mechanism. Often, the template entry is a dummy host which doesn't actually exist and never sends bootp requests. This feature is similar to the tc feature of termcap(5) for similar terminals. Note that bootpd allows the tc tag symbol to appear anywhere in the host entry, unlike termcap which requires it to be the last tag. Information explicitly specified for a host always overrides information implied by a tc tag symbol, regardless of its location within the entry. The value of the tc tag may be the hostname or IP address of any host entry previously listed in the configuration file.
Sometimes it is necessary to delete a specific tag after it has been inferred via tc. This can be done using the construction tag@ which removes the effect of tag as in termcap(5). For example, to completely undo an IEN-116 name server specification, use ":ns@:" at an appropriate place in the configuration entry. After removal with @, a tag is eligible to be set again through the tc mechanism.
Blank lines and lines beginning with "#" are ignored in the configuration file. Host entries are separated from one another by newlines; a single host entry may be extended over multiple lines if the lines end with a backslash (\). It is also acceptable for lines to be longer than 80 characters. Tags may appear in any order, with the following exceptions: the hostname must be the very first field in an entry, and the hardware type must precede the hardware address.
An example /etc/bootptab file follows:
# Sample bootptab file
default1:\
:hd=/usr/boot:bf=null:\
:ds=128.2.35.50 128.2.13.21:\
:ns=0x80020b4d 0x80020ffd:\
:ts=0x80020b4d 0x80020ffd:\
:sm=255.255.0.0:gw=0x8002fe24:\
:hn:vm=auto:to=-18000:\
:T37=0x12345927AD3BCF:T99="Special ASCII string":
carnegie:ht=6:ha=7FF8100000AF:ip=128.2.11.1:tc=default1:
baldwin:ht=1:ha=0800200159C3:ip=128.2.11.10:tc=default1:
wylie:ht=1:ha=00DD00CADF00:ip=128.2.11.100:tc=default1:
arnold:ht=1:ha=0800200102AD:ip=128.2.11.102:tc=default1:
bairdford:ht=1:ha=08002B02A2F9:ip=128.2.11.103:tc=default1:
bakerstown:ht=1:ha=08002B0287C8:ip=128.2.11.104:tc=default1:
# Special domain name server for next host
butlerjct:ht=1:ha=08002001560D:ip=128.2.11.108:ds=128.2.13.42:tc=default1:
gastonville:ht=6:ha=7FFF81000A47:ip=128.2.11.115:tc=default1:
hahntown:ht=6:ha=7FFF81000434:ip=128.2.11.117:tc=default1:
hickman:ht=6:ha=7FFF810001BA:ip=128.2.11.118:tc=default1:
lowber:ht=1:ha=00DD00CAF000:ip=128.2.11.121:tc=default1:
mtoliver:ht=1:ha=00DD00FE1600:ip=128.2.11.122:tc=default1: