dhcpd.8

来自「minix操作系统最新版本（3.1.1）的源代码」· 8 代码 · 共 209 行

.TH DHCPD 8
.SH NAME
dhcpd \- dynamic host configuration protocol daemon
.SH SYNOPSIS
.in +.5i
.ti -.5i
.B dhdpd
.RB [ \-qar ]
.RB [ \-t [\fIlevel\fP]]
.RB [ \-d [\fIlevel\fP]]
.RB [ \-f
.IR configfile ]
.RB [ \-c
.IR cachefile ]
.RB [ \-p
.IR poolfile ]
.RI [ host " ...]"
.in -.5i
.SH DESCRIPTION
.de SP
.if t .sp 0.4
.if n .sp
..
.B Dhcpd
is a client and a server for the Dynamic Host Configuration Protocol.  As a
client it collects DHCP data to configure the Ethernet networks with, and as
a server it answers DHCP queries from other machines.
.PP
This manual page describes the operation of
.BR dhcpd ,
the associated configuration file is described in
.BR dhcp.conf (5).
(The latter, together with
.BR boot (8),
is of more practical value when it comes to getting a machine's networks
interfaces up and running.  See the options section below for debugging DCHP
problems.)
.SS Initialization
On a normal startup, i.e. none of the
.BR \-q ,
.BR \-a
or
.BR \-r
options are given,
.B dhcpd
determines what IP devices are present, and which of those are Ethernets.
For each network it looks for information in the configuration file as if
it were a server answering a query for that network.  If any information is
found then the IP address is configured and the information stored in the
cache file.
.SS "Client Operation"
For each still unconfigured network a DHCP DISCOVER request is broadcast on
that network.  If a DHCP OFFER reply is received then a DHCP REQUEST is
broadcast for the IP address offered, and if a DHCP ACK is received then the
network is configured and the information stored in the cache file.
.PP
If no reply is received then another query is sent after 4 seconds, and then
again after 8 seconds, doubling each time until 64 seconds.  Every 64
seconds thereafter a request is broadcast until a reply is received.
.PP
Once configured the DHCP lease, rebind and renew times are computed.  At the
renew time a DHCP REQUEST is sent to the DHCP server to extend the lease.
Normally we get an answer and refresh our information, but if no reply is
received we wait for half the remaining time until the rebind time and keep
retrying and halving the remaining time.  When the rebind time is reached
the DHCP REQUEST is broadcast to try and reach some other DHCP server.
Halving the remaining time again and again until the lease expires.  At that
point we go back to square one and broadcast a DHCP DISCOVER.
.PP
If at any point a DHCP NAK is received we start over completely.  After a
DHCP OFFER an ARP request is transmitted just before the DHCP REQUEST to
check if the address offered is already in use.  If an ARP reply is received
before the DHCP ACK then after the ACK we send a DHCP DECLINE to the server
to tell that the address isn't what we want and again we start over.
.SS "Router Discovery"
The gateway offered by the DHCP server is made known to the TCP/IP server by
sending an ICMP router advertisement to the local interface with a short
lifetime and a low priority.  Then up to three router solicitations are
broadcast three seconds apart to look for a router.  If a router answers
with a router advertisement then we no longer worry about routing for that
interface.  Otherwise the router information is refreshed before it expires
and another solicitation is sent out.  This happens about twice an hour.
.SS "Server Operation"
Once all networks so marked are configured the daemon starts answering
requests by other machines or relaying requests to other DHCP servers.
DHCP requests are answered if information for a client
can be found in the configuration file, or if a free address can be found in
the pool file, or if a client rerequests an address it already owns.
.PP
If the daemon is both a server and a relay for a network then it will try
to answer a request and only relay if it has no answer.
.SS "Nothing more to do?"
If the daemon finds out that all networks have an infinite lease (configured
with a fixed address), there is no router information to keep warm, and
it isn't a server then it simply exits.
.SS "Asynchronous I/O?"
MINIX 3 doesn't have the asynchronous I/O that Minix-vmd has, so under MINIX 3
the daemon only works with one network at a time.  If it's stuck on the same
network for 32 seconds then that network is closed and another network is
tried for 32 seconds.  This usually works ok as a client, but as a server it
can only handle one network.
.SH OPTIONS
.TP
.B \-q
Read and print the cache and pool file contents, showing DHCP information
for each network, and the IP addresses in the pool with lease times and
current/last owners of those addresses.
.TP
.B \-a
Add the named hosts (or IP addresses) to the pool file.
.TP
.B \-r
Remove hosts from the pool file.
.TP
.RB [ \-t [\fIlevel\fP]]
Set the test level (by default 1).  At test level 1 all networks are seen as
unconfigured, will not be configured and no data will be put in the cache.
The program will just act as-if.  At test level 2 the interfaces will not be
configured from the configuration file, the data must come from a remote
server.  At level 3 the renewal, rebind and lease time will be 60, 120
and 180 seconds.  At level 4 these times will be 60, 60, and 120.  At
level 5 these times will be 60, 60, and 60.  These test levels are meant
to debug the DHCP client code, and are best used with a high debug level.
.TP
.RB [ \-d [\fIlevel\fP]]
Set the debug level (by default 1).  At debug level 1 the program shows
Ethernet and IP addresses as they are determined or configured, DHCP
messages sent and received with little detail (one line per message), and
memory use.  At debug level 2 each DHCP packet is decoded and shown in
detail.  At debug level 3 device opens and closes are shown.  The debugging
level may also be increased by 1 at runtime by sending signal
.BR SIGUSR1
or turned off (set to 0) with
.BR SIGUSR2 .
.TP
.BI \-f " configfile"
Names the configuration file, by default
.BR /etc/dhcp.conf .
.TP
.BI \-c " cachefile"
Names the cache file, by default
.BR /usr/adm/dhcp.cache .
.TP
.BI \-p " poolfile"
Names the IP address pool, by default
.BR /usr/adm/dhcp.pool .
.SH "SEE ALSO"
.BR RFC-2131 ,
.BR RFC-1533 ,
.BR dhcp.conf (5),
.BR hosts (5),
.BR ifconfig (8),
.BR inet (8),
.BR boot (8),
.BR inetd (8),
.BR nonamed (8).
.SH DIAGNOSTICS
.TP
"'/etc/dhcp.conf', line ..."
The program exits on any configuration file error.  You have to correct the
error and restart the program.
.TP
"No lease set for address ..."
There must be a lease time defined for addresses in the pool.  Correct and
restart the program.
.TP
"###### declines #.#.#.# saying '...'"
A client with the given client identifier (usually 01 followed by the client's
Ethernet address) declines an IP address, hopefully with a message telling
why.  This usually means that the IP address is already in use by another
host.  This program, acting as a client, will tell what other host in its
message, but Windows has no additional info alas.
.TP
"Got a NAK from #.#.#.# [through #.#.#.#] saying '...'"
The server with the given IP address doesn't want us to have or keep the IP
address we were offered or are rerequesting.  This could mean that the server
has forgotten about us and has given our address to another machine.  This
is bad if our lease hasn't yet expired.  There may be a relay involved, and
there may even be a text message with precise information.
.TP
"#.#.#.# offered by #.#.#.# is already in use by #:#:#:#:#:#"
We got an ARP reply for an offered address.  We won't accept it, and send
out a DECLINE when we get an ACK.
.TP
"DHCP packet too big, ..."
You've got way to much information in the configuration file, more than fits
in a minimum size DHCP packet.  (Notify the author if you really need to send
more information.  He doesn't think anyone needs to.)
.TP
"Pool table is corrupt"
You will have to remove and refill the pool file.  Chaos may ensue if
there are active clients and they don't use ARP to detect each other.
(Most do.)
.SH BUGS
There is no randomization of timers.  Modern systems don't blink under the
load of several clients broadcasting a few packets in sync.
.PP
There is no extra time spent waiting for an ARP reply.  It is assumed that
any IP stack will immediately respond, so that the DHCP server can't
possibly beat it at sending out an ACK.  (The DHCP server has to commit the
lease to stable storage first anyway.)
.PP
Way more nonsense can be sent in a DHCP packet that MINIX 3 could do
something with, but nobody does so we don't bother.
.PP
DHCP was invented by a rabid gerbil on speed.
.SH AUTHOR
Kees J. Bot <[e-mail]>