BOOTP(1M-SysV) RISC/os Reference Manual BOOTP(1M-SysV)
NAME
bootp - server for DARPA Bootstrap Protocol (BOOTP)
SYNOPSIS
/usr/etc/bootp [ -d ] [ -f ]
DESCRIPTION
bootp is a server which supports the DARPA Bootstrap Proto-
col (BOOTP). This protocol is designed to allow a (possibly
diskless) client machine to determine its own Internet
address, the address of a boot server and the name of an
appropriate boot file to be loaded and executed. BOOTP does
not provide the actual transfer of the boot file, which is
typically done with a simple file transfer protocol such as
TFTP. A detailed protocol specification for BOOTP is con-
tained in RFC 951.
The BOOTP protocol uses UDP/IP as its transport mechanism.
The BOOTP server receives service requests at the UDP port
indicated in the ``bootp'' service description contained in
the file /etc/services (see services(4)). The BOOTP server
is started by inetd(1M), as configured in the inetd.conf
file.
The basic operation of the BOOTP protocol is a single packet
exchange as follows:
1) The booting client machine broadcasts a BOOTP request
packet to the BOOTP server UDP port, using a UDP broad-
cast or the equivalent thereof. The request packet
includes the following information:
requestor's Ethernet address
requestor's Internet address (optional)
desired server's name (optional)
boot file name (optional)
2) All the BOOTP servers on the same Ethernet wire as the
client machine receive the client's request. If the
client has specified a particular server, then only
that server will respond.
3) The server looks up the requestor in its configuration
file by Internet address or Ethernet address, in that
order of preference. (The BOOTP configuration file is
described below.) If the Internet address was not
specified by the requestor and a configuration record
is not found, the server will look in the /etc/ethers
file (see ethers(4)) for an entry with the client's
Ethernet address. If an entry is found, the server
will check the hostname of that entry against the
/etc/hosts file (see hosts(4)) in order to complete the
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Ethernet address to Internet address mapping. If the
BOOTP request does not include the client's Internet
address and the server is unable to translate the
client's Ethernet address into an Internet address by
either of the two methods described, the server will
not respond to the request.
4) The server performs name translation on the boot
filename requested and then checks for the presence of
that file. If the file is present, then the server
will send a response packet to the requestor which
includes the following information:
the requestor's Internet address
the server's Internet address
the Internet address of a gateway to the server
the server's name
vendor specific information (not defined by the protocol)
If the boot file is missing, the server will return a
response packet with a null filename, but only if the
request was specifically directed to that server. The
pathname translation is: if the boot filename is
rooted, use it as is; else concatenate the root of the
boot subtree, as specified by the BOOTP configuration
file, followed by the filename supplied by the reques-
tor, followed by a period and the requestor's hostname.
If that file is not present, remove the trailing period
and host name and try again. If no boot filename is
requested, use the default boot file for that host from
the configuration table. If there is no default speci-
fied for that host, use the general default boot
filename, first with .hostname as a suffix and then
without.
Options
The -d option causes bootp to generate debugging messages.
All messages from bootp go through syslogd(8), the system
logging daemon.
The -f option enables the forwarding function of bootp.
Refer to the following section on Booting Through Gateways
for an explanation.
Bootp Configuration File
In order to perform its name translation and address resolu-
tion functions, bootp requires configuration information,
which it gets from an ASCII file called /usr/etc/bootptab
and from other system configuration files like /etc/ethers
and /etc/hosts. Here is a sample bootptab file:
#
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# /usr/etc/bootptab: database for bootp server
#
# Blank lines and lines beginning with '#' are ignored.
#
# root of boot subtree
/usr/local/boot
# default bootfile
unix
%%
#
# The remainder of this file contains one line per client
# interface with the information shown by the table headings
# below. The 'host' name is also tried as a suffix for the
# 'bootfile' when searching the boot directory.
# (e.g., bootfile.host)
#
# host htype haddr iaddr bootfile
#
unixbox 1 1:2:3:4:bb:cc 89.0.0.2
The fields of each line may be separated by variable amounts
of white space (blanks and tabs). The first section, up to
the line beginning '%%', defines the place where bootp looks
for boot files when the client requests a boot file using a
non-rooted pathname. The second section of the file is used
for mapping client Ethernet addresses into Internet
addresses. The htype field should always have a value of 1
for now, which indicates that the hardware address is a 48-
bit Ethernet address. The haddr field is the Ethernet
address of the system in question expressed as 6 hex bytes
separated by colons. The iaddr field is the 32-bit Internet
address of the system expressed in standard dot notation (4
byte values in decimal, in network order, separated by
periods). Each line in the second section can also specify
a default boot file for each specific host. In the example
above, if the host called unixbox makes a BOOTP request with
no boot file specified, the server will select the first of
the following that it finds:
/usr/local/boot/unix.unixbox
/usr/local/boot/unix
It is not necessary to create a record for every potential
client the every bootptab file. The only constraint is that
bootp will only respond to a request from a client if it can
deduce the client's Internet address. There are three ways
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that this can happen: 1) the client already knows his
Internet address and includes it in the BOOTP request
packet, 2) there is an entry in /usr/etc/bootptab that
matches the client's Ethernet address or 3) there are
entries in the /etc/ethers and /etc/hosts files (or their
Network Information Service equivalents) that allow the
client's Ethernet address to be translated into an Internet
address.
Booting Through Gateways
Since the BOOTP request is distributed using a UDP broad-
cast, it will only be received by other hosts on the same
Ethernet cable as the client. In some cases the client may
wish to boot from a host on another network. This can be
accomplished by using the forwarding function of BOOTP
servers on the local wire. To use BOOTP forwarding, there
must be a bootp process running in a gateway machine on the
local cable. A gateway machine is simply a machine with
more than one Ethernet controller board. The gateway bootp
must be invoked with the -f option to activate forwarding.
Such a forwarding bootp will resend any BOOTP request it
receives that asks for a specific host by name, if that host
is on a different network from the client that sent the
request. The BOOTP server forwards the packet using the
full routing capabilities of the underlying IP layer in the
kernel, so the forwarded packet will automatically be routed
to the requested BOOTP server provided that the kernel rout-
ing tables contain a route to the destination network.
DIAGNOSTICS
The BOOTP server sends any messages it wants to reach the
outside world through the system logging daemon, syslogd(8).
The actual disposition of these messages depends on the con-
figuration of syslogd on the machine in question. Consult
syslogd(8) for further information.
bootp can produce the following messages:
'get interface config' ioctl failed (message)
'get interface netmask' ioctl failed (message)
getsockname fails (message)
forwarding failed (message)
send failed (message)
set arp ioctl failed
Each of the above messages mean that a system call has
returned an error unexpectedly. Such errors usually
cause bootp to terminate. The message will be the
result of calling perror(3) with the errno value that
was returned.
less than two interfaces, -f flag
Warning only. Means that the -f option was specified
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on a machine that is not a gateway. Forwarding only
works on gateways.
request for unknown host xxx from
Information only. A BOOTP request was received asking
for host xxx, but that host is not in the host data-
base. The request was generated by yyy, which may be
given as a host name or an Internet address.
request from xxx for 'fff'
Information only. bootp logs each request for a boot
file. The means that host xxx has requested boot file
fff.
boot file fff missing
A request has been received for the boot file fff, but
that file doesn't exist.
replyfile fff
Information only. bootp has selected the file fff as
the boot file to satisfy a request.
forward request with gateway address already
The server has received a reply to be forwarded to a
requestor, but some other bootp has already filled him-
self in as the gateway. This is an error in the BOOTP
forwarding mechanism.
missing gateway address
This means that this bootp has generated a response to
a client and is trying to send the response directly to
the client (i.e. the request did not get forwarded by
another bootp), but none of the Ethernet interfaces on
this machine is on the same wire as the client machine.
This indicates a bug in the BOOTP forwarding mechanism.
can't open /usr/etc/bootptab
The bootp configuration file is missing or has wrong
permissions.
(re)reading /usr/etc/bootptab
Information only. bootp checks the modification date
of the configuration file on the receipt of each
request and rereads it if it has been modified since
the last time it was read.
bad hex address: xxx at line
bad internet address: sss at line
string truncated: sss, on line nnn
These messages all mean that the format of the BOOTP
configuration file is not valid.
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'hosts' table length exceeded
There are too many lines in the second section of the
BOOTP configuration file. The current limit is 512.
can't allocate memory
A call to malloc(3) failed.
gethostbyname(sss) fails (message)
A call to gethostbyname(3N) with the argument sss has
failed.
gethostbyaddr(dd.dd.dd.dd) fails (message)
A call to gethostbyaddr (see gethostbyname(3N)) with
the argument dd.dd.dd.dd has failed.
can't find source net for address
This means that the server has received a datagram with
a source address that doesn't make sense. The offend-
ing address is printed as a 32 bit hexadecimal number
xxx.
SEE ALSO
inetd(1M), tftpd(1M), syslogd(8).
ethers(4), hosts(4), services(4) in the Programmer's Refer-
ence Manual.
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