How Solaris DHCP Client Manages Network Configuration Information
After the information packet is obtained
from a DHCP server, dhcpagent configures the network interface
and brings it up, controlling the interface for the duration of the lease
time for the IP address. The dhcpagent daemon maintains
the configuration data in an internal table held in memory. The system startup
scripts use the dhcpinfo command to extract configuration
option values from the dhcpagent daemon's table. The values
are used to configure the system and enable it to join the network.
The agent waits passively until a period of time elapses, usually half
the lease time, and then requests an extension of the lease from a DHCP server.
If the dhcpagent daemon finds that the interface is down
or the IP address has changed, it does not control the interface until it
is instructed by the ifconfig command to do so. If the dhcpagent daemon finds that the interface is up and the IP address
hasn't changed, it sends a request to the server for a lease renewal. If the
lease cannot be renewed, the dhcpagent daemon takes down
the interface at the end of the lease time.
DHCP Client Management
The Solaris DHCP client does not require management under normal
system operation. It automatically starts when the system boots, renegotiates
leases, and stops when the system shuts down. You cannot manually start and
stop the dhcpagent daemon. However, you can use the ifconfig command as superuser on the client system to affect the
client's management of the network interface if necessary.
ifconfig Command Options Used With DHCP Client
The ifconfig command
enables you to:
Start the DHCP client -
The command ifconfig interface dhcp start initiates the interaction between the DHCP client and DHCP server
to obtain an IP address and a new set of configuration options. This might
be useful when you change information that you want a client to use immediately,
such as when you add IP addresses or change the subnet mask.
Request network configuration information
only - The command ifconfig interface dhcp inform causes dhcpagent to
issue a request for network configuration parameters, with the exception of
the IP address. This is useful for situations where the network interface
has a valid IP address, but the client system needs updated network options.
For example, this might be useful if you do not use DHCP to manage IP addresses,
but do use it to configure hosts on the network.
Request a lease extension -
The command ifconfig interface dhcp extend causes dhcpagent to issue a request to renew
the lease. This happens automatically, but you might want to use this command
if you change the lease time and want clients to use the new lease time immediately
rather than waiting for the next attempt at lease renewal.
Release the IP address -
The command ifconfig interface dhcp release causes dhcpagent to relinquish the IP address
used by the network interface. This happens automatically when the lease expires.
You might want to issue this command if the lease time is long and you need
to take down the network interface for an extended period of time or you want
to remove the system from the network.
Drop the IP address -
The command ifconfig interface dhcp drop causes dhcpagent to take down the network interface
without informing the DHCP server that it is doing so. This enables the client
to use the same IP address when it reboots.
Ping the network interface -
The command ifconfig interface dhcp ping lets you test to see if the interface is under the control of DHCP.
View DHCP configuration status of
the network interface - The command ifconfig interface dhcp status displays the current state of
the DHCP client. The display indicates the following: If an IP address has been bound to the client
Number of requests sent, received, and declined
If this is the primary interface
Times when the lease was obtained, when it expires, and when
attempts to renew it will or did start
For example:
# ifconfig hme0 dhcp status
Interface State Sent Recv Declined Flags
hme0 BOUND 1 1 0 [PRIMARY]
(Began,Expires,Renew)=(08/16/2000 15:27, 08/18/2000 13:31, 08/17/2000 15:24)
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DHCP Client Parameter File
The file /etc/default/dhcpagent
on the client system contains tunable parameters for the dhcpagent daemon. You can use a text editor to change several parameters
that affect client operation. The file is well documented so you should refer
to the file for more information, as well as referring to the dhcpagent man page.
DHCP Client Shutdown
When the system running the DHCP client shuts down normally, the dhcpagent daemon writes the current configuration information to
the file /etc/dhcp/interface.dhc.
The lease is dropped rather than released, so the DHCP server does not know
that the IP address is not in active use.
If the lease is still valid when the system reboots, the DHCP client
sends an abbreviated request to use the same IP address and network configuration
information it had used before the system rebooted. If the DHCP server permits
this, the client can use the information that it wrote to disk when the system
shut down. If the server does not permit the client to use the information,
the client initiates the DHCP protocol sequence described previously and obtains
new network configuration information.
DHCP Client Systems and Name Services
Solaris systems support the following name services: DNS, NIS, NIS+,
and a local file store (/etc/hosts). Each name service
requires some configuration before it is usable. The name service switch
configuration file (see nsswitch.conf(4)) must also be set up appropriately to
indicate the name services to be used.
Before a DHCP client system can use a name service, you must configure
the system as a client of the name service.
The following table summarizes issues related to each name service and
DHCP, and includes links to documentation that can help you set up clients
for each name service.
Table 7-4 Name Service Client Setup Information for DHCP Client Systems
Name Service | Client
Setup Notes |
|---|
NIS | If you are installing the Solaris operating environment on a client system by using
Solaris DHCP, you can use a configuration macro that contains the NISservs and NISdmain options to pass the IP
addresses of NIS servers and the NIS domain name to the client. The client
then automatically becomes a NIS client. If a DHCP client system
is already running the Solaris operating environment, the NIS client is not
automatically configured on that system when the DHCP server sends NIS information
to the client. If the DHCP server is configured to send NIS information
to the DHCP client system, you can see the values given to the client if you
use the dhcpinfo command on the client as follows: # /sbin/dhcpinfo NISdmain # /sbin/dhcpinfo
NISservs Use the values returned for the NIS domain
name and NIS servers when you set up the system as a NIS client. You set up a NIS client for a Solaris DHCP client system in the standard way,
as documented in "Setting Up and Configuring NIS Service" in System Administration
Guide: Naming and Directory Services (DNS, NIS, and LDAP).
Note - You can write a script that uses dhcpinfo
and ypinit to automate NIS client configuration on DHCP
client systems.
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NIS+ | If the DHCP client system
receives a nonreserved IP address (the address may not always be the same),
you must set up the NIS+ client for a DHCP client system in a nonstandard
way, which is documented in Setting Up DHCP Clients as NIS+ Clients. This procedure
is necessary because NIS+ uses security measures to authenticate requests
for service. The security measures depend upon the IP address. If the DHCP client system has been manually assigned an IP address (the client's
address is always the same), you can set up the NIS+ client in the standard
way, which is documented in "Setting Up NIS+ Client Machines" in System Administration Guide: Naming and Directory Services (FNS and NIS+) |
/etc/inet/hosts | You must set up the /etc/inet/hosts file for a DHCP client
system that is to use /etc/inet/hosts for its name service. The DHCP client system's host name is added to its own /etc/inet/hosts file by the DHCP tools. However, you must add the
host name manually to the /etc/inet/hosts files of other
systems in the network. If the DHCP server system uses /etc/inet/hosts for name resolution, you must also add the client's host name
manually on the system. |
DNS | If the DHCP client system receives the DNS domain name through DHCP, the client
system's /etc/resolv.conf file is configured automatically.
To actually use DNS on systems that use /etc/inet/hosts
files, you must modify the /etc/nsswitch.conf file to add dns to the hosts line. See "Adding and Deleting Clients" in System Administration Guide: Naming and Directory Services
(DNS, NIS, and LDAP) for more information about DNS clients. If the client system uses NIS or NIS+ for local name resolution,
you should be aware of the following: NIS - If the NIS server allows DNS forwarding (which
it does by default), the NIS client system can also use DNS. No further DNS
client setup is needed in this case. If the NIS server does not
allow DNS forwarding, the client system can use DNS by becoming a DNS client
as described in "Adding and Deleting Clients" in System Administration Guide:
Naming and Directory Services (DNS, NIS, and LDAP). Note
that if the client receives the DNS domain name from the DHCP server, the /etc/resolv.conf file needed for a DNS client is configured automatically,
so you need only be concerned with the nsswitch.conf file. NIS+ - The NIS+ client system can be configured to also
use DNS if you edit the nsswitch.conffile to add dns to the hosts line.
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Client Host Name Registration
If you let the DHCP server generate host names for the IP addresses
you place in the DHCP service, the DHCP server can register those host names
in NIS+, /etc/inet/hosts, or DNS name services. Host name
registration cannot be done in NIS because NIS does not provide a protocol
to allow programs to update and propagate NIS maps.
Note - The DHCP server can update DNS with generated host names only
if the DNS server and DHCP server are running on the same system.
If a DHCP client provides its host name and the DNS server is configured
to allow dynamic updates from the DHCP server, the DHCP server can update
DNS on the client's behalf, even if the DNS and DHCP servers are running on
different systems. See Enabling Dynamic DNS Updates by DHCP Server for more information
about enabling this feature.
The following table summarizes client host name registration for DHCP
client systems with the various name services.
Table 7-5 Client Host Name Registration in Name Services
| Who Registers Host Name |
|---|
Name Service | DHCP Generated Host Name | DHCP Client Supplied Host Name |
|---|
NIS | NIS Administrator | NIS Administrator |
NIS+ | DHCP tools | DHCP tools |
/etc/hosts | DHCP tools | DHCP tools |
DNS | DHCP tools, if the DNS server
runs on the same system as the DHCP server. DNS Administrator,
if the DNS sever runs on a different system. | DHCP
server, if configured for dynamic DNS updates. DNS Administrator,
if DHCP server is not so configured. |
Note that Solaris DHCP clients can request particular host names in
DHCP requests if configured to do so as described in How to Enable a Solaris Client to Request Specific Host Name.
Please consult the documentation for non-Solaris clients to determine if the
capability is supported.
DHCP Client Systems With Multiple Network Interfaces
The DHCP client
daemon can manage several different interfaces on one system simultaneously,
each with its own IP address and lease time. If more than one network interface
is configured for DHCP, the client issues separate requests to configure them
and maintains a separate set of network configuration options for each interface.
However, although the parameters are stored separately, some of the parameters
are global in nature, applying to the system as a whole, rather than to a
particular network interface.
Options such as hostname, NIS domain name, and timezone are global parameters
and should have the same values for each interface, but these values may differ
due to errors in the information entered by the DHCP administrator. To ensure
that there is only one answer to a query for a global parameter, only the
parameters for the primary network interface are requested. You can insert
the word primary in the /etc/dhcp.interface file for the interface you want to be treated as the
primary interface.
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