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。
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切換到后台：
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就是切換到后台指令，-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。
對於 -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
使用busybox下的simple.script
進入busybox目錄：busybox1.19.2/example/udhcp/，拷貝文件simple.script到根文件系統的/usr/share/udhcpc/目錄下，
更名為default.script，再將default.script中resolv_conf=”/etc/resolv.conf”更改為resolv_conf=”/tmp/resolv.conf”。
(說明：由於測試使用cramfs文件系統，etc目錄不可寫，運行udhcpc無法在/etc目錄下創建resolv.conf文件。)