EzDoum

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         Set client identifier.  Type is first char.

-C, --clientid-none             Suppress default client identifier

-V, --vendorclass=CLASSID       Set vendor class identifier

-H, --hostname=HOSTNAME         Client hostname

-h,                             Alias for -H

-F, --fqdn=FQDN                 Client fully qualified domain name

-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)

-t, --retries=NUM               Send up to NUM request packets

-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. udhcpc never does

any configuration of the network interface itself, but instead relies on

a set of scripts. 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 must 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

	mask		- The number of bits in the netmask (ie: 24)

	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).