DHCPCLIENT(2)DHCPCLIENT(2)NAME
Dhcpclient: Bootconf, Lease, bootp, dhcp, applycfg, removecfg -
client's side of dynamic host configuration protocol
SYNOPSIS
include "dhcp.m"; # sic
dhcpclient := load Dhcpclient Dhcpclient->PATH;
Bootconf, Lease: import dhcpclient;
Bootconf: adt {
ip: string;
ipgw: string;
ipmask: string;
bootf: string;
bootip: string;
dhcpip: string;
siaddr: string;
serverid: string;
sys: string;
dom: string;
lease: int;
options: array of array of byte;
vendor: array of array of byte;
new: fn(): ref Bootconf;
get: fn(c: self ref Bootconf, n: int): array of byte;
getint: fn(c: self ref Bootconf, n: int): int;
getip: fn(c: self ref Bootconf, n: int): string;
getips: fn(c: self ref Bootconf, n: int): list of string;
gets: fn(c: self ref Bootconf, n: int): string;
put: fn(c: self ref Bootconf, n: int, a: array of byte);
putint: fn(c: self ref Bootconf, n: int, v: int);
putips: fn(c: self ref Bootconf, n: int, ips: list of string);
puts: fn(c: self ref Bootconf, n: int, s: string);
};
Lease: adt {
configs: chan of (ref Bootconf, string);
release: fn(l: self ref Lease);
};
init: fn();
tracing: fn(debug: int);
bootp: fn(net: string, ctlifc: ref Sys->FD, device: string,
init: ref Bootconf): (ref Bootconf, string);
dhcp: fn(net: string, ctlifc: ref Sys->FD, device: string,
init: ref Bootconf, options: array of int):
(ref Bootconf, ref Lease, string);
applycfg: fn(net: string, ctlifc: ref Sys->FD,
conf: ref Bootconf): string;
removecfg: fn(net: string, ctlifc: ref Sys->FD,
conf: ref Bootconf): string;
DESCRIPTION
Dhcpclient implements the client side of the Dynamic Host Configuration
Protocol (DHCP) of Internet RFC2131. In the interface, Internet
addresses are represented as strings, in forms that ip(2) can parse,
and that can be written directly to control files in ip(3).
Init must be called before invoking any other operation of the module.
Bootp reserves the UDP port on net for use by BOOTP/DHCP clients, and
sends a BOOTP request (ie, one without a DHCP operation code). Net is
the name of the network directory (if nil, the default is /net). If
bootp is to configure the interface according to the results received,
ctlifc should be open on the control file of the net/ipifc directory
for the interface to be configured; otherwise it should be nil. Bootp
repeats the request periodically until it either receives a reply or
has made 5 attempts. It returns a tuple (conf, err). If it has
received a reply, conf refers to a Bootconf value that contains the
values received, and err is nil. If ctlifc is not nil, the interface
will also have been configured appropriately. If a valid reply has not
been received, or some other error occurred, conf is nil, and err is a
diagnostic.
Dhcp has a similar interface, but runs the full DHCP protocol. The
options array has integers representing possible DHCP options; dhcp
asks the server to provide values for them. If options is nil, a few
option values are requested that might be useful for Inferno (eg, sub‐
net mask, gateway, DNS server, authentication and file servers, and so
on). If the server does supply them, they can be retrieved either from
specific fields of Bootconf, or using its get operations. Init is also
usually nil, but can refer to a Bootconf that provides some values to
suggest to the server, for instance if the client knows a previously-
assigned address stored in non-volatile memory. Dhcp returns a tuple
(conf, lease, err), where conf and err are just as for bootp, and the
new component lease is a reference to a Lease value that gives access
to the state of the client's address assignment.
DHCP allows a server to assign a client an address permanently, or to
lease it for a specified time. In the latter case, Bootconf.lease will
have a non-zero value, and the client must periodically renew the lease
to retain the address, and dhcp creates a process to do so. The Lease
value provides a way for that process to communicate changes (if any)
to the network configuration. Each time the configuration changes, the
process will send a message on the channel configs. (The channel is
buffered, and dhcp first discards any previous notifications not yet
received, so there are no ill effects if no process ever receives from
the channel.) Each message is a tuple (conf, diag). If a new state
change has been made successfully, conf refers to a Bootconf value with
the details. Otherwise, conf is nil and diag explains what went wrong.
In any case, the watchdog process continues to try to extend the lease,
or failing that, obtain a new network configuration, perhaps from
another server. Lease.release may be called to release the leased
address and stop the watchdog.
Bootconf has the following operations:
new() Return a reference to a Bootconf with values initialised to nil
or 0.
bc.get(n)
Return the value of DHCP option n as a raw array of bytes.
Return nil if the option is not set.
bc.getint(n)
Return the value of option n interpreted as an integer. Return
zero if the option is not set.
bc.getip(n)
Return the first Internet address provided for option n.
bc.getips(n)
Return a list of all the Internet addresses provided for option
n.
bc.gets(n)
Return the value of option n as a string.
bc.put(n, a)
Set the value of DHCP option n to the bytes of byte array a. If
a is nil, put removes any existing value for the option.
bc.putint(n, v)
Set option n to the integer value v.
bc.putips(n, ips)
Set option n to the list of Internet addresses ips.
bc.puts(n, s)
Set option n to the string n.
Dhcpclient names a few constants representing commonly-used configura‐
tion options (attributes). They are suitable parameters for the option
selector n of Bootconf's get and put functions. The first set of con‐
stants name options for both BOOTP and DHCP:
Odnsserver Internet address(es) of Domain Name Servers
Odomainname Current domain (see Bootconf.dom)
Ohostname Host name (see Bootconf.sys)
Omask Network mask (IPv4). Also see Boot‐
conf.ipmask.
Onetbiosns NetBIOS servers
Ontpserver Network Time Protocol servers
Opop3server POP3 mail servers
Orouter Default router for subnet (see Bootconf.ipgw)
Osmtpserver SMTP mail delivery servers
Ovendorinfo Vendor-specific data (see below)
Owwwserver HTTP proxy
The second set has DHCP options:
Obootfile Name of the file containing a kernel for the
client to load (eg, by TFTP); see Boot‐
conf.bootf.
Olease Lease time for IP address, in seconds (also
see Bootconf.lease)
Omaxmsg Maximum DHCP size the client is willing to
accept (minimum 576 bytes).
Orebindingtime Time interval in seconds from address assign‐
ment to the time address must be rebound.
Orenewaltime Time interval in seconds from address assign‐
ment to first attempt to renew the address.
Otftpserver TFTP server from which to fetch kernel and
parameter files; see Bootconf.bootip.
Ovendorclass Identify vendor type and configuration of
client. Inferno sets this to plan9_386 (sic)
to encourage Plan 9 DHCP servers to respond;
other servers will ignore it.
The final set give vendor-specific options that Inferno shares with
Plan 9:
Ovendor Flag OR'd in to an option number to mark it as
destined for the `vendor information' section.
OP9auth Authentication server (Ovendor|129)
OP9fs File server (Ovendor|128)
Given a network configuration in conf, and a valid file descriptor for
a network interface's control file, in the network net, applycfg sets
the basic interface parameters (address, network mask, default gate‐
way), and writes other parameters to net/ndb; conversely, removecfg
removes from the interface just those parameters set by conf. Normally
these functions are called automatically, as required, by dhcp and its
watchdog process.
SOURCE
/appl/lib/dhcpclient.b
SEE ALSObootpd(8), dhcp(8)DHCPCLIENT(2)
