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Solaris DHCP Client


DHCP Protocol

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The Solaris DHCP client is a daemon (dhcpagent ). DHCP clients from other vendors can also use the services of the Solaris DHCP server.

The DHCP clientís process ( dhcpagent ):

The Solaris DHCP client is installed and enabled on a system during installation of the Solaris when you specify that you want to use DHCP to configure network interfaces.

DHCP Client Startup

The dhcpagent daemon obtains configuration information that is needed by other processes involved in booting the system. For this reason, dhcpagent is started early in the boot process by the system startup scripts; booting is suspended until the network configuration information is obtained or timeout occurs. 

The presence of the file /etc/dhcp.interface (for example, /etc/dhcp.hme0) indicates to the startup scripts that DHCP is to be used on the specified interface. Upon finding a dhcp.interface file, the startup scripts start the dhcpagent .

After starting up, dhcpagent waits until it receives instructions to configure a network interface.

The startup scripts issue the ifconfig interface dhcp start command, which instructs dhcpagent to start DHCP. If commands are contained within the dhcp.interface file, they are appended to the dhcp start option of ifconfig . See the ifconfig  man page for more information about options used with dhcp .

How 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. dhcpagent 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 ís table.

The values are used in configuring the system and becoming part of the network.

The agent waits passively until a set period elapses (usually half the lease time) and then requests an extension of the lease from a DHCP server.

If dhcpagent finds that the interface is down or the IP address has changed, it does not control the interface until it is instructed by ifconfig to do so.

If dhcpagent finds that the interface is up and the IP address hasnít changed, it sends a request to the server for a lease renewal. If the lease cannot be renewed, dhcpagent takes the interface down at the end of the lease time.

DHCP Client Management

The Solaris DHCP client does not need to be managed 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 machine to affect the clientís management of the network interface if necessary.

ifconfig Commands Used With DHCP Client

The ifconfig command lets you:

DHCP Client Parameter File

The file /etc/default/dhcpagent on the client system contains tunable parameters for dhcpagent . You can use a text editor to change several parameters that affect client operation.

The file is well-documented so please refer to the file for more information about the parameters.

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 is rebooted, the DHCP client sends an abbreviated request to use the same IP address and network configuration information it had used before the system was 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 using the information, the client initiates the DHCP protocol sequence described previously and obtains new network configuration information.

DHCP Clients 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 it might not be the case 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.

You can use DHCP services in a network you are creating, or in an existing network.

If you are setting up a network, see Chapter 5 before attempting to set up DHCP services. If you have an existing network, continue in this chapter.

This chapter describes what you need to do before setting up DHCP service on your network.

The planning information is targeted for use with DHCP Manager, although you can also use the command-line utility dhcpconfig to set up DHCP service.


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