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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.
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The DHCP client’s 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.
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 .
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 ’s 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 hasn’t 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.
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 client’s management of the network interface if necessary.
The ifconfig command lets you:
This might be useful when you change options on the server, such as adding
IP addresses or changing the subnet mask, that you want clients to use immediately.
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
for configuring hosts on the network.
This happens automatically, but you might want to use this 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.
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 are removing the system from
the network.
This enables the client to use the same IP address when it reboots.
The display includes information about whether an IP address has been bound to the client; the number of requests sent, received, and declined; flags indicating whether this is the primary interface; and times indicating when the lease was obtained, expires, and when attempts to renew it will/did start. For example:
# ifconfig hme0 dhcp status Interface State Sent Recv Declined Flags hme0 BOUND 1 1 0 [PRIMARY] (Began, Expires, Renew) = (07/15/1999 15:27, 07/17/1999 13:31, 07/16/ 1999 15:24)
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.
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.
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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