由于要使用網絡通訊，所以不可避免的要用到dhcp。理想的網絡通訊方式是下面3種都要支持:

　　1,接入已有網絡。這便要求可以作為dhcp客戶端。

　　2,作為DHCP服務器，動態分配IP。

　　3,指定固定IP

　　第3種情況沒有什么好說的，簡單說下前2種情況。

　　使用步驟：

　　（1）在內核的網絡項里面把DHCP配置上；

　　（2）在busybox里面把[*]udhcp server(udhcpd)

　　[*]udhcp client(udhcpc)都選上。

　　udhcpd就是終端設備作為DHCP服務器

　　udhcpc就是終端設備作為DHCP客戶端

　　busybox里面對dhcp都已經給出例子了，

　　[zhh@localhost busybox-1.14.1]$ ls ./examples/udhcp/

　　sample.bound? sample.deconfig? sample.nak? sample.renew? sample.script? simple.script? udhcpd.conf

　　比如使用udhcpc時

　　就可以直接把simple.script拿來使用，改不改名字都可以，busybox里面默認的目錄文件是/usr/share/udhcpc/default.script

　　可以查看下幫助

　　# udhcpc --help

　　BusyBox v1.14.1 (2010-01-22 10:35:16 CST) multi-call binary

　　Usage: udhcpc [-Cfbnqtvo] [-c CID] [-V VCLS] [-H HOSTNAME] [-i INTERFACE]

　　[-p pidfile] [-r IP] [-s script] [-O dhcp-option]... [-P N]

　　-V CLASSID????? Vendor class identifier

　　-i INTERFACE??? Interface to use (default: eth0)

　　-H,-h HOSTNAME? Client hostname

　　-c CLIENTID???? Client identifier

　　-C????????????? Suppress default client identifier

　　-p file???????? Create pidfile

　　-r IP?????????? IP address to request

　　-s file???????? Run file at DHCP events (default /usr/share/udhcpc/default.script)

　　-t N??????????? Send up to N request packets

　　-T N??????????? Try to get a lease for N seconds (default 3)

　　-A N??????????? Wait N seconds (default 20) after failure

　　-O OPT????????? Request DHCP option OPT (cumulative)

　　-o????????????? Do not request any options (unless -O is also given)

　　-f????????????? Run in foreground

　　-b????????????? Background if lease is not immediately obtained

　　-S????????????? Log to syslog too

　　-n????????????? Exit with failure if lease is not immediately obtained

　　-q????????????? Quit after obtaining lease

　　-R????????????? Release IP on quit

　　-P N??????????? Use port N instead of default 68

　　-a????????????? Use arping to validate offered address

　　#

　　這樣就很好理解了。

　　下面就說說使用udhcpd，同樣可以直接把busybox自帶的udhcpd.conf作為參考，怎么設置該文件就不詳述了，去參考相關文檔即可。看看udhcpd怎么使用

　　# udhcpd --help

　　BusyBox v1.14.1 (2010-01-22 10:35:16 CST) multi-call binary

　　Usage: udhcpd [-fS] [-P N] [configfile]

　　DHCP server

　　-f????? Run in foreground

　　-S????? Log to syslog too

　　-P N??? Use port N instead of default 67

　　幫助一目了然。

　　我使用的時候直接

　　#udhcpd /etc/udhcpd.conf

　　即可。

　　還有一個租約文件要簡要說說，使用udhcpd時會要求建立一個租約文件，按照提示創建一個就行了，它起什么作用呢？就是為了記錄客戶端所獲得的IP，如果沒有租約文件，則會重新給客戶端分配一個新IP，如果有，則使用原先分配的IP。

?

例如：udhcpc -i wlan0是獲取wlan0的ip地址，如果想獲取之后直接退出，添加 -q參數，即：udhcpc -q -i wlan0

?

udhcpc切換到后臺：

它自帶參數可以實現該功能。如下：

?? udhcpc -b -i eth0 -p /var/run/udhcpc.pid -R

解釋一下，-b就是切換到后臺指令，-i是指定使用哪個網絡接口，雙網卡的時候一定要使用它來指定eth0? or ?eth1。

對于 -R參數，其實也很重要，在關閉udhcpc時，可以向dhcpserver發送release取消租約。

?

udhcpc scripts

Here's some debian scripts I wrote for udhcpc 0.9.6. I wanted to make it easy to run local scripts for DHCP changes so I created /etc/udhcpc.d. All the /usr/share/udhcpc/default.* scripts have been merged into /etc/udhcpc.d/S50default. S99local is an example script that patches resolv.conf and calls a DNS update script.

/etc/init.d/udhcpc

/etc/udhcpc.script

/etc/udhcpc.d/S50default

/etc/udhcpc.d/S99local

?

http://udhcp.busybox.net/README.udhcpc

udhcp client (udhcpc)

--------------------

The udhcp client negotiates a lease with the DHCP server and notifies

a set of scripts when a leases is obtained or lost.

command line options

-------------------

The command line options for the udhcp client are:

-c, --clientid=CLIENTID Client identifier

-H, --hostname=HOSTNAME Client hostname

-h, Alias for -H

-f, --foreground Do not fork after getting lease

-b, --background Fork to background if lease cannot be

immediately negotiated.

-i, --interface=INTERFACE Interface to use (default: eth0)

-n, --now Exit with failure if lease cannot be

immediately negotiated.

-p, --pidfile=file Store process ID of daemon in file

-q, --quit Quit after obtaining lease

-r, --request=IP IP address to request (default: none)

-s, --script=file Run file at dhcp events (default:

/usr/share/udhcpc/default.script)

-v, --version Display version

If the requested IP address cannot be obtained, the client accepts the

address that the server offers.

udhcp client scripts

-------------------

When an event occurs, udhcpc calls the action script. The script by

default is /usr/share/udhcpc/default.script but this can be changed via?

the command line arguments. The three possible arguments to the script?

are:

deconfig: This argument is used when udhcpc starts, and

when a leases is lost. The script should put the interface in an

up, but deconfigured state, ie: ifconfig $interface 0.0.0.0.

bound: This argument is used when udhcpc moves from an

unbound, to a bound state. All of the paramaters are set in

enviromental variables, The script should configure the interface,

and set any other relavent parameters (default gateway, dns server,?

etc).

renew: This argument is used when a DHCP lease is renewed. All of

the paramaters are set in enviromental variables. This argument is

used when the interface is already configured, so the IP address,

will not change, however, the other DHCP paramaters, such as the

default gateway, subnet mask, and dns server may change.

nak: This argument is used with udhcpc receives a NAK message.

The script with the deconfig argument will be called directly

afterwards, so no changes to the network interface are neccessary.

This hook is provided for purely informational purposes (the

message option may contain a reason for the NAK).

The paramaters for enviromental variables are as follows:

$HOME - The set $HOME env or "/"

$PATH - the set $PATH env or "/bin:/usr/bin:/sbin:/usr/sbin"

$1 - What action the script should perform

interface - The interface this was obtained on

ip - The obtained IP

siaddr - The bootp next server option

sname - The bootp server name option

boot_file - The bootp boot file option

subnet - The assigend subnet mask

timezone - Offset in seconds from UTC

router - A list of routers

timesvr - A list of time servers

namesvr - A list of IEN 116 name servers

dns - A list of DNS server

logsvr - A list of MIT-LCS UDP log servers

cookiesvr - A list of RFC 865 cookie servers

lprsvr - A list of LPR servers

hostname - The assigned hostname

bootsize - The length in 512 octect blocks of the bootfile

domain - The domain name of the network

swapsvr - The IP address of the client's swap server

rootpath - The path name of the client's root disk

ipttl - The TTL to use for this network

mtu - The MTU to use for this network

broadcast - The broadcast address for this network

ntpsrv - A list of NTP servers

wins - A list of WINS servers

lease - The lease time, in seconds

dhcptype - DHCP message type (safely ignored)

serverid - The IP of the server

message - Reason for a DHCPNAK

tftp - The TFTP server name

bootfile - The bootfile name

additional options are easily added in options.c.

note on udhcpc's random seed

---------------------------

udhcpc will seed its random number generator (used for generating xid's)

by reading /dev/urandom. If you have a lot of embedded systems on the same

network, with no entropy, you can either seed /dev/urandom by a method of

your own, or doing the following on startup:

ifconfig eth0 > /dev/urandom

in order to seed /dev/urandom with some data (mac address) unique to your

system. If reading /dev/urandom fails, udhcpc will fall back to its old

behavior of seeding with time(0).

signals accepted by udhcpc

-------------------------

udhcpc also responds to SIGUSR1 and SIGUSR2. SIGUSR1 will force a renew state,

and SIGUSR2 will force a release of the current lease, and cause udhcpc to

go into an inactive state (until it is killed, or receives a SIGUSR1). You do

not need to sleep between sending signals, as signals received are processed

sequencially in the order they are received.

compile time options

-------------------

options.c contains a set of dhcp options for the client:

name[10]: The name of the option as it will appear in scripts

flags: The type of option, as well as if it will be requested

by the client (OPTION_REQ)

code: The DHCP code for this option

?實現DHCP自動獲取IP地址?

分類： LINUX

前提：系統已經實現DNS（即使用pingwww.baidu.com測試時能ping通）。

1．?在內核中添加以下選項：

Networking? --->

?? [*] Networking support ?

? ? ? Networking options? --->?

? ? ? ? ? <* > Packet socket ? ? ? ? ? ? ? ? //添加.配置CONFIG_PACKET

? ? ? ? ? [ * ] ? ? IP: DHCP support ? ? ? ? //添加

? ? ? ? ? [ * ] Network packet filtering (replaces ipchains)? --->? ? //添加，后面子選項可不選，配置CONFIG_NETFILTER

說明：若沒選<* > Packet socket, [ * ] Network packet filtering (replaces ipchains)? --->選項，在執行udhcpc命令時出現如下錯誤：

~ # udhcpc

udhcpc (v0.9.9-pre) started

udhcpc[208]: udhcpc (v0.9.9-pre) started

?

FATAL: couldn't listen on socket, Address family not supported by protocol

udhcpc[208]: FATAL: couldn't listen on socket, Address family not supported by protocol

2．? Busybox中添加以下選項：

Networking Utilities? --->

?? udhcp Server/Client? --->

? ? ? ? [] udhcp Server (udhcpd) ? ? ? //在此不作服務端，故不選。生成udhcpd命令? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

? ? ? ? [*] udhcp Client (udhcpc) ? ? ? //生成udhcpc命令? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

? ? ? ? [ ] Lease display utility (dumpleases) ? ? ? ? ? ? ? ? ? ? ? ?

? ? ? ? [ ] ? Log udhcp messages to syslog (instead of stdout) ? ? ? ?

? ? ? ? [ ] ? Compile udhcp with noisy debugging messages

若busybox沒編譯相應選項，也可從網上下載相應文件，用arm-linux交叉編譯得到udhcpd,udhcpc命令copy到usr/sbin下就可以了。

我從 網上? 下的udhcp_0.9.8cvs20050303.orig.tar.gz文件

解壓后修改Makefile文件

在19行添加CROSS_COMPILE=arm-linux- ?

注釋12行的COMBINED_BINARY=1，否則不生成udhcpc命令。

3．?建相關配置文件

從busybox的examples/udhcp/下copy? simple.script文件到開發板/usr/share/udhcpc/下，并重命名為default.script，udhcp_0.9.8cvs20050303.orig.tar.gz中也有這樣的文件。

[root@localhost root]# vi usr/share/udhcpc/default.script

#!/bin/sh

?

# udhcpc script edited by Tim Riker <Tim@Rikers.org>

?

[ -z "$1" ] && echo "Error: should be called from udhcpc" && exit 1

?

RESOLV_CONF="/etc/resolv.conf"

[ -n "$broadcast" ] && BROADCAST="broadcast $broadcast"

[ -n "$subnet" ] && NETMASK="netmask $subnet"

?

case "$1" in

? ? ? ? deconfig)

? ? ? ? ? ? ? ? /sbin/ifconfig $interface 0.0.0.0

? ? ? ? ? ? ? ? ;;

?

? ? ? ? renew|bound)

? ? ? ? ? ? ? ? /sbin/ifconfig $interface $ip $BROADCAST $NETMASK

?

? ? ? ? ? ? ? ? if [ -n "$router" ] ; then

? ? ? ? ? ? ? ? ? ? ? ? echo "deleting routers"

? ? ? ? ? ? ? ? ? ? ? ? while route del default gw 0.0.0.0 dev $interface ; do

? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? :

? ? ? ? ? ? ? ? ? ? ? ? done

? ? ? ? ? ? ? ? ? ? ? ? for i in $router ; do

? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? route add default gw $i dev $interface

? ? ? ? ? ? ? ? ? ? ? ? done

? ? ? ? ? ? ? ? fi

?

? ? ? ? ? ? ? ? echo -n > $RESOLV_CONF

? ? ? ? ? ? ? ? [ -n "$domain" ] && echo search $domain >> $RESOLV_CONF

? ? ? ? ? ? ? ? for i in $dns ; do

? ? ? ? ? ? ? ? ? ? ? ? echo adding dns $i

? ? ? ? ? ? ? ? ? ? ? ? echo nameserver $i >> $RESOLV_CONF

? ? ? ? ? ? ? ? done

? ? ? ? ? ? ? ? ;;

esac

?

exit 0

?

4．?重啟開發板，執行udhcpc就可自動獲取IP地址了，以下是執行udhcpc的輸出信息：

?

~ # udhcpc

udhcpc (v0.9.9-pre) started

udhcpc[228]: udhcpc (v0.9.9-pre) started

?

Sending discover...

udhcpc[228]: Sending discover...

?

Sending select for 192.168.1.109...

udhcpc[228]: Sending select for 192.168.1.109...

?

Lease of 192.168.1.109 obtained, lease time 86400

udhcpc[228]: Lease of 192.168.1.109 obtained, lease time 86400

?

deleting routers

route: SIOC[ADD|DEL]RT: No such process

adding dns 192.168.0.1

~ # ping www.baidu.com

PING www.a.shifen.com (220.181.38.4): 56 data bytes

64 bytes from 220.181.38.4: icmp_seq=0 ttl=52 time=1219.0 ms

[1] + Stopped? ? ? ? ? ? ? ? ? ? ping www.baidu.com

?

5．?如果是雙網卡必須用參數指明

例：udhcpc? -i? eth1?