illumos: manual page: dhcpagent.8

DHCPAGENT(8) Maintenance Commands and Procedures DHCPAGENT(8)

NAME

dhcpagent - Dynamic Host Configuration Protocol (DHCP) client daemon

SYNOPSIS

dhcpagent [-a] [ -d n] [-f] [-v]

DESCRIPTION

dhcpagent implements the client half of the Dynamic Host Configuration
Protocol (DHCP) for machines running illumos software.

The dhcpagent daemon obtains configuration parameters for the client
(local) machine's network interfaces from a DHCP server. These parameters
may include a lease on an IP address, which gives the client machine use
of the address for the period of the lease, which may be infinite. If the
client wishes to use the IP address for a period longer than the lease,
it must negotiate an extension using DHCP. For this reason, dhcpagent
must run as a daemon, terminating only when the client machine powers
down.

For IPv4, the dhcpagent daemon is controlled through ipadm(8),
nwamcfg(8), or ifconfig(8) in much the same way that the init(8) daemon
is controlled by telinit(8). dhcpagent can be invoked as a user process,
albeit one requiring root privileges, but this is not necessary, as
ipadm(8), nwamcfg(8), or ifconfig(8) will start dhcpagent automatically.

For IPv6, the dhcpagent daemon is invoked automatically by in.ndpd(8). It
can also be controlled through ifconfig(8), if necessary.

When invoked, dhcpagent enters a passive state while it awaits
instructions from ipadm(8), nwamcfg(8), ifconfig(8), or in.ndpd(8). When
dhcpagent receives a command to configure an interface, dhcpagent brings
up the interface (if necessary) and starts DHCP. Once DHCP is complete,
dhcpagent can be queried for the values of the various network
parameters. In addition, if DHCP was used to obtain a lease on an address
for an interface, dhcpagent configures the address for use. When a lease
is obtained, it is automatically renewed as necessary. If the lease
cannot be renewed, dhcpagent will unconfigure the address, but the
interface will be left up, and dhcpagent will attempt to acquire a new
address lease.

dhcpagent monitors system suspend/resume events and will validate any
non-permanent leases with the DHCP server upon resume. Similarly,
dhcpagent monitors link up/down events and will validate any non-
permanent leases with the DHCP server when the downed link is brought
back up. The lease validation mechanism will restart DHCP if the server
indicates that the existing lease is no longer valid. If the server
cannot be contacted, then the existing lease will continue. This behavior
can be modified with the VERIFIED_LEASE_ONLY parameter in the
/etc/default/dhcpagent file. See the description of this parameter
below.

For IPv4, if the configured interface is found to be unplumbed, or to
have a different IP address, subnet mask, or broadcast address from those
obtained from DHCP, the interface is abandoned from DHCP control.

For IPv6, dhcpagent automatically plumbs and unplumbs logical interfaces
as necessary for the IPv6 addresses supplied by the server. The IPv6
prefix length (netmask) is not set by the DHCPv6 protocol, but is instead
set by in.ndpd(8) using prefix information obtained by Router
Advertisements. If any of the logical interfaces created by dhcpagent is
unplumbed, or configured with a different IP address, it will be
abandoned from DHCP control. If the link-local interface is unplumbed,
then all addresses configured by DHCP on that physical interface will be
removed.

In addition to DHCP, dhcpagent also supports BOOTP (IPv4 only). See RFC
951, Bootstrap Protocol. Configuration parameters obtained from a BOOTP
server are treated identically to those received from a DHCP server,
except that the IP address received from a BOOTP server always has an
infinite lease.

DHCP also acts as a mechanism to configure other information needed by
the client, for example, the domain name and addresses of routers. Aside
from the IP address, and for IPv4 alone, the netmask, broadcast address,
and default router, the agent does not directly configure the
workstation, but instead acts as a database which may be interrogated by
other programs, and in particular by dhcpinfo(1).

On clients with a single interface, this is quite straightforward.
Clients with multiple interfaces may present difficulties, as it is
possible that some information arriving on different interfaces may need
to be merged, or may be inconsistent. Furthermore, the configuration of
the interfaces is asynchronous, so requests may arrive while some or all
of the interfaces are still unconfigured. To handle these cases, one
interface may be designated as primary, which makes it the authoritative
source for the values of DHCP parameters in the case where no specific
interface is requested. See dhcpinfo(1) and ifconfig(8) for details.

For IPv4, the dhcpagent daemon can be configured to request a particular
Fully Qualified Domain Name (FQDN) or host name. See the REQUEST_FQDN or
REQUEST_HOSTNAME description in the FILES section. When first configuring
a client to request an FQDN or host name, you must perform the following
steps as root to ensure that the full DHCP negotiation takes place:

# pkill dhcpagent
# rm /etc/dhcp/interface.dhc
# reboot

All DHCP packets sent by dhcpagent include a vendor class identifier (RFC
2132, option code 60; RFC 3315, option code 16). This identifier is the
same as the platform name returned by the uname -i command, except:

o Any commas in the platform name are changed to periods.

o If the name does not start with a stock symbol and a comma, it
is automatically prefixed with SUNW.

Messages

The dhcpagent daemon writes information and error messages in five
categories:

critical

Critical messages indicate severe conditions that prevent proper
operation.

errors

Error messages are important, sometimes unrecoverable events due to
resource exhaustion and other unexpected failure of system calls;
ignoring errors may lead to degraded functionality.

warnings

Warnings indicate less severe problems, and in most cases, describe
unusual or incorrect datagrams received from servers, or requests for
service that cannot be provided.

informational

Informational messages provide key pieces of information that can be
useful to debugging a DHCP configuration at a site. Informational
messages are generally controlled by the -v option. However, certain
critical pieces of information, such as the IP address obtained, are
always provided.

debug

Debugging messages, which may be generated at two different levels of
verbosity, are chiefly of benefit to persons having access to source
code, but may be useful as well in debugging difficult DHCP
configuration problems. Debugging messages are only generated when
using the -d option.

When dhcpagent is run without the -f option, all messages are sent to the
system logger syslog(3C) at the appropriate matching priority and with a
facility identifier LOG_DAEMON. When dhcpagent is run with the -f option,
all messages are directed to standard error.

DHCP Events and User-Defined Actions
If an executable (binary or script) is placed at /etc/dhcp/eventhook, the
dhcpagent daemon will automatically run that program when any of the
following events occur:

BOUND and BOUND6

These events occur during interface configuration. The event program
is invoked when dhcpagent receives the DHCPv4 ACK or DHCPv6 Reply
message from the DHCP server for the lease request of an address,
indicating successful initial configuration of the interface. (See
also the INFORM and INFORM6 events, which occur when configuration
parameters are obtained without address leases.)

EXTEND and EXTEND6

These events occur during lease extension. The event program is
invoked just after dhcpagent receives the DHCPv4 ACK or DHCPv6 Reply
from the DHCP server for the DHCPv4 REQUEST (renew) message or the
DHCPv6 Renew or Rebind message.

Note that with DHCPv6, the server might choose to remove some
addresses, add new address leases, and ignore (allow to expire) still
other addresses in a given Reply message. The EXTEND6 event occurs
when a Reply is received that leaves one or more address leases still
valid, even if the Reply message does not extend the lease for any
address. The event program is invoked just before any addresses are
removed, but just after any new addresses are added. Those to be
removed will be marked with the IFF_DEPRECATED flag.

EXPIRE and EXPIRE6

These events occur during lease expiration. For DHCPv4, the event
program is invoked just before the leased address is removed from an
interface. For DHCPv6, the event program is invoked just before the
last remaining leased addresses are removed from the interface.

DROP and DROP6

These events occur during the period when an interface is dropped.
The event program is invoked just before the interface is removed
from DHCP control. If the interface has been abandoned due the user
unplumbing the interface, then this event will occur after the user's
action has taken place. The interface might not be present.

INFORM and INFORM6

These events occur when an interface acquires new or updated
configuration information from a DHCP server by means of the DHCPv4
INFORM or the DHCPv6 Information-Request message. These messages are
sent using an ifconfig(8) dhcp inform command or when the DHCPv6
Router Advertisement O (letter 0) bit is set and the M bit is not
set. Thus, these events occur when the DHCP client does not obtain
an IP address lease from the server, and instead obtains only
configuration parameters.

LOSS6

This event occurs during lease expiration when one or more valid
leases still remain. The event program is invoked just before expired
addresses are removed. Those being removed will be marked with the
IFF_DEPRECATED flag.

Note that this event is not associated with the receipt of the Reply
message, which occurs only when one or more valid leases remain, and
occurs only with DHCPv6. If all leases have expired, then the EXPIRE6
event occurs instead.

RELEASE and RELEASE6

This event occurs during the period when a leased address is
released. The event program is invoked just before dhcpagent
relinquishes the address on an interface and sends the DHCPv4 RELEASE
or DHCPv6 Release packet to the DHCP server.

The system does not provide a default event program. The file
/etc/dhcp/eventhook is expected to be owned by root and have a mode of
755.

The event program will be passed two arguments, the interface name and
the event name, respectively. For DHCPv6, the interface name is the name
of the physical interface.

The event program can use the dhcpinfo(1) utility to fetch additional
information about the interface. While the event program is invoked on
every event defined above, it can ignore those events in which it is not
interested. The event program runs with the same privileges and
environment as dhcpagent itself, except that stdin, stdout, and stderr
are redirected to /dev/null. Note that this means that the event program
runs with root privileges.

If an invocation of the event program does not exit after 55 seconds, it
is sent a SIGTERM signal. If does not exit within the next three seconds,
it is terminated by a SIGKILL signal.

See EXAMPLES for an example event program.

OPTIONS

The following options are supported:

-a

Adopt a configured IPv4 interface. This option is for use with
diskless DHCP clients. In the case of diskless DHCP, DHCP has already
been performed on the network interface providing the operating
system image prior to running dhcpagent. This option instructs the
agent to take over control of the interface. It is intended primarily
for use in boot scripts.

The effect of this option depends on whether the interface is being
adopted.

If the interface is being adopted, the following conditions apply:

dhcpagent uses the client id specified in /chosen:<client_id>, as
published by the PROM or as specified on a boot(8) command line. If
this value is not present, the client id is undefined. The DHCP
server then determines what to use as a client id. It is an error
condition if the interface is an Infiniband interface and the PROM
value is not present.

If the interface is not being adopted:

dhcpagent uses the value stored in /etc/default/dhcpagent. If this
value is not present, the client id is undefined. If the interface is
Infiniband and there is no value in /etc/default/dhcpagent, a client
id is generated as described by the draft document on DHCP over
Infiniband, available at:

http://www.ietf.org

-d n

Set debug level to n. Two levels of debugging are currently
available, 1 and 2; the latter is more verbose.

-f

Run in the foreground instead of as a daemon process. When this
option is used, messages are sent to standard error instead of to
syslog(3C).

-v

Provide verbose output useful for debugging site configuration
problems.

EXAMPLES

Example 1: Example Event Program

The following script is stored in the file /etc/dhcp/eventhook, owned by
root with a mode of 755. It is invoked upon the occurrence of the events
listed in the file.

#!/bin/sh

(
echo "Interface name: " $1
echo "Event: " $2

case $2 in
"BOUND")
echo "Address acquired from server "\
`/sbin/dhcpinfo -i $1 ServerID`
;;
"BOUND6")
echo "Addresses acquired from server " \
`/sbin/dhcpinfo -v6 -i $1 ServerID`
;;
"EXTEND")
echo "Lease extended for " \
`/sbin/dhcpinfo -i $1 LeaseTim`" seconds"
;;
"EXTEND6")
echo "New lease information obtained on $i"
;;
"EXPIRE" | "DROP" | "RELEASE")
;;

esac
) >/var/run/dhcp_eventhook_output 2>&1

Note the redirection of stdout and stderr to a file.

FILES

/etc/dhcp/if.dhc
/etc/dhcp/if.dh6

Contains the configuration for interface. The mere existence of this
file does not imply that the configuration is correct, since the
lease might have expired. On start-up, dhcpagent confirms the
validity of the address using REQUEST (for DHCPv4) or Confirm
(DHCPv6).

/etc/dhcp/duid
/etc/dhcp/iaid

Contains persistent storage for system-generated DUID (DHCP Unique
Identifier) and interface-specific IAID (Identity Association
Identifier) values which are used if no CLIENT_ID is defined (see
below). The format of these files is undocumented, and applications
should not read from or write to them. Instead, dhcpinfo(1) can be
used to query the dhcpagent for ClientID. For DHCPv6 interfaces, the
result will contain the DUID. For DHCPv4 interfaces with
V4_DEFAULT_IAID_DUID enabled (see below), the result will contain the
IAID and DUID.

/etc/default/dhcpagent

Contains default values for tunable parameters. All values may be
qualified with the interface they apply to by prepending the
interface name and a period (".") to the interface parameter name.
The parameters include: the interface parameter name.

To configure IPv6 parameters, place the string .v6 between the
interface name (if any) and the parameter name. For example, to set
the global IPv6 parameter request list, use .v6.PARAM_REQUEST_LIST.
To set the CLIENT_ID (DUID) on hme0, use hme0.v6.CLIENT_ID.

The parameters include:

VERIFIED_LEASE_ONLY

Indicates that a RELEASE rather than a DROP should be performed
on managed interfaces when the agent terminates. Release causes
the client to discard the lease, and the server to make the
address available again. Drop causes the client to record the
lease in /etc/dhcp/interface.dhc or /etc/dhcp/interface.dh6 for
later use. In addition, when the link status changes to up or
when the system is resumed after a suspend, the client will
verify the lease with the server. If the server is unreachable
for verification, then the old lease will be discarded (even if
it has time remaining) and a new one obtained.

Enabling this option is often desirable on mobile systems, such
as laptops, to allow the system to recover quickly from moves.

Default value of this option is no.

OFFER_WAIT

Indicates how long to wait in seconds between checking for valid
OFFERs after sending a DISCOVER. For DHCPv6, sets the time to
wait between checking for valid Advertisements after sending a
Solicit.

Default value of this option is 3.

CLIENT_ID

Indicates the value that should be used to uniquely identify the
client to the server. This value can take one of three basic
forms:

decimal,data...
0xHHHHH...
"string...."

The first form is an RFC 3315 DUID. This is legal for both IPv4
DHCP and DHCPv6. For IPv4, an RFC 4361 Client ID is constructed
from this value. In this first form, the format of data...
depends on the decimal value. The following formats are defined
for this first form:

1,hwtype,time,lla

Type 1, DUID-LLT. The hwtype value is an integer in the range
0-65535, and indicates the type of hardware. The time value
is the number of seconds since midnight, January 1st, 2000
UTC, and can be omitted to use the current system time. The
lla value is either a colon-separated MAC address or the name
of a physical interface. If the name of an interface is used,
the hwtype value can be omitted. For example: 1,,,hme0

2,enterprise,hex...

Type 2, DUID-EN. The enterprise value is an integer in the
range 0-4294967295 and represents the SMI Enterprise number
for an organization. The hex string is an even-length
sequence of hexadecimal digits.

3,hwtype,lla

Type 3, DUID-LL. This is the same as DUID-LLT (type 1),
except that a time stamp is not used.

*,hex

Any other type value (0 or 4-65535) can be used with an even-
length hexadecimal string.

The second and third forms of CLIENT_ID are legal for IPv4 only.
These both represent raw Client ID (without RFC 4361), in hex, or
NVT ASCII string format. Thus, "Sun" and 0x53756E are equivalent.

V4_DEFAULT_IAID_DUID

Indicates whether to use, when CLIENT_ID is not defined, a
system-managed, RFC 3315-style (i.e., DHCPv6-style) binding
identifier as documented in RFC 4361, "Node-specific Client
Identifiers for DHCPv4," for IPv4 interfaces which for purposes
of backward compatibility do not normally get default binding
identifiers.

An IPv4 interface that is not in an IP network multipathing
(IPMP) group, that is not IP over InfiniBand (IPoIB), and that is
not a logical interface does not normally get a default binding
identifier.

Default value of this option is no.

PARAM_REQUEST_LIST

Specifies a list of comma-separated integer values of options for
which the client would like values, or symbolic Site or Option
option names. Symbolic option names for IPv4 are resolved
through /etc/dhcp/inittab. Option names for IPv6 are resolved by
means of /etc/dhcp/inittab6.

PARAM_IGNORE_LIST

Specifies a list of options (constructed in the same manner as
PARAM_REQUEST_LIST) that the DHCP client will ignore. Ignored
options are treated as though the server did not return the
options specified. Ignored options are not visible using
dhcpinfo(1) or acted on by the client. This parameter can be
used, for example, to disable an unwanted client name or default
router.

REQUEST_FQDN

Indicates the client requests the DHCP server to map the client's
leased IPv4 address to the Fully Qualified Domain Name (FQDN)
associated with the network interface that performs DHCP on the
client and to collaborate with a compatible DNS server to manage
A and PTR resource records for the FQDN for the life of the
lease.

The hostname in the FQDN is determined from the following
possible configurations:

1. ipadm(8): include the -1,--primary flag when creating an
address that uses DHCP so that nodename(5) is used as the
hostname.

2. ipadm(8): include the -h,--reqhost hostname switch when
executing the create-addr -T dhcp subcommand, or use the set-
addrprop -p reqhost=hostname subcommand for any existing DHCP
address.

3. nwamcfg(8): set a property, ip-primary=on, for an ncu ip that
uses DHCP so that nodename(5) is used as the hostname.

4. nwamcfg(8): set a property, ip-reqhost=hostname, for an ncu
ip that uses DHCP.

The hostname value is either a Partially Qualified Domain Name
(PQDN) or an FQDN (i.e., a "rooted" domain name ending with a '.'
or one inferred to be an FQDN if it contains at least three DNS
labels such as srv.example.com). If a PQDN is specified, then an
FQDN is constructed if DNS_DOMAINNAME is defined or if
ADOPT_DOMAINNAME is set to yes and an eligible domain name (as
described below) is available.

If an FQDN is sent, REQUEST_HOSTNAME processing will not be done,
per RFC 4702 (3.1): "clients that send the Client FQDN option in
their messages MUST NOT also send the Host Name."

Default value of this option is yes.

DNS_DOMAINNAME

Indicates the value that should be appended to a PQDN specified
by the -h,--reqhost option of ipadm(8), by the ncu ip-reqhost
property of nwamcfg(8), or by nodename(5) to construct an FQDN
for REQUEST_FQDN processing. If the hostname value is already an
FQDN, then the value of this option is not used.

ADOPT_DOMAINNAME

Indicates that a domain name returned by the DHCP server or the
domain from resolv.conf(5) should be adopted if needed to
construct an FQDN from a PQDN specified by the -h,--reqhost
option of ipadm(8), by the ncu ip-reqhost property of nwamcfg(8),
or by nodename(5). If the hostname value is already an FQDN,
then the value of this option is not applicable. The eligible
DHCP option for domain name is DHCPv4 DNSdmain.

Default value of this option is no.

REQUEST_HOSTNAME

Indicates the client requests the DHCP server to map the client's
leased IPv4 address to the host name associated with the network
interface that performs DHCP on the client. The host name must be
specified as documented for a PQDN in REQUEST_FQDN above or
specified in the /etc/hostname.interface file for the relevant
interface on a line of the form

inet hostname

where hostname is the host name requested.

This option works with DHCPv4 only.

Default value of this option is yes.

/etc/dhcp/eventhook

Location of a DHCP event program.

ATTRIBUTES

NOTES

The dhcpagent daemon can be used on IPv4 logical interfaces, just as with
physical interfaces. When used on a logical interface, the daemon
automatically constructs a Client ID value based on the DUID and IAID
values, according to RFC 4361. The /etc/default/dhcpagent CLIENT_ID
value, if any, overrides this automatic identifier.

As with physical IPv4 interfaces, the /etc/hostname.hme0:1 and
/etc/dhcp.hme0:1 files must also be created in order for hme0:1 to be
automatically plumbed and configured at boot. In addition, unlike
physical IPv4 interfaces, dhcpagent does not add or remove default routes
associated with logical interfaces.

DHCP can be performed on IPMP IP interfaces to acquire and maintain IPMP
data addresses. Because an IPMP IP interface has no hardware address, the
daemon automatically constructs a Client ID using the same approach
described above for IPv4 logical interfaces. In addition, the lack of a
hardware address means the daemon must set the "broadcast" flag in all
DISCOVER and REQUEST messages on IPMP IP interfaces. Some DHCP servers
may refuse such requests.

DHCP can be performed on IP interfaces that are part of an IPMP group (to
acquire and maintain test addresses). The daemon will automatically set
the NOFAILOVER and DEPRECATED flags on each test address. Additionally,
the daemon will not add or remove default routes in this case. Note that
the actual DHCP packet exchange may be performed over any active IP
interface in the IPMP group. It is strongly recommended that test
addresses have infinite leases. Otherwise, an extended network outage
detectable only by probes may cause test address leases to expire,
causing in.mpathd(8) to revert to link-based failure detection and
trigger an erroneous repair.

With DHCPv6, the link-local interface must be configured using
/etc/hostname6.hme0 in order for DHCPv6 to run on hme0 at boot time. The
logical interfaces for each address are plumbed by dhcpagent
automatically.

February 13, 2020 DHCPAGENT(8)