208 lines
8.4 KiB
Groff
208 lines
8.4 KiB
Groff
.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 doesn't have the asynchronous I/O that Minix-vmd has, so under Minix
|
|
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 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 <kjb@cs.vu.nl>
|