Panasonic DX-600, Руководство по обслуживанию

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268
DX-600/800
APR 2002
Edition 1.0
7.12. Dynamic Host Configuration Protocol (DHCP) - Extended Feature
DHCP is based on the Bootstrap Protocol (BOOTP), adding the capability of automatic allocation of
reusable network addresses and additional configuration options.
The Dynamic Host Configuration Protocol (DHCP) provides configuration parameters to Internet hosts.
The Bootstrap Protocol (BOOTP) is a UDP/IP-based protocol which allows a booting host to configure itself
dynamically and without user supervision. BOOTP provides a means to notify a host of its assigned IP
address, the IP address of a boot server host, and the name of a file to be loaded into memory and
executed. Other configuration information such as the local subnet mask, the local time offset, the
addresses of default routers, and the addresses of various Internet servers can also be communicated to a
host using BOOTP.
DHCP consists of two components: a protocol for delivering host-specific configuration parameters
from a DHCP server to a host and a mechanism for allocation of network addresses to hosts.
DHCP supports three mechanisms for IP address allocation.
In "automatic allocation", DHCP assigns a permanent IP address to a client.
In "dynamic allocation", DHCP assigns an IP address to a client for a limited period of time (or until the
client explicitly relinquishes the address).
In "manual allocation", a client’s IP address is assigned by the network administrator, and DHCP is used
simply to convey the assigned address to the client. A particular network will use one or more of these
mechanisms, depending on the policies of the network administrator.
"DHCP client"
A DHCP client is an Internet host using DHCP to obtain configuration parameters such as a network
address.
"DHCP server"
A DHCP server is an Internet host that returns configuration parameters to DHCP clients.
Table 1 describes a DHCP message and its purpose of use.
Table 1: DHCP messages and purpose of use
Message Use
DHCPDISCOVER Client broadcast to locate available servers.
DHCPOFFER Server to client in response to DHCPDISCOVER with offer of configuration
parameters.
DHCPREQUEST Client message to servers either (a) requesting offered parameters from one server
and implicitly declining offers from all others, (b) confirming correctness of
previously allocated address after, e.g., system reboot, or (c) extending the lease
on a particular network address.
DHCPACK Server to client with configuration parameters, including committed network
address.
DHCPNAK Server to client indicating client’s notion of network address is incorrect (e.g., client
has moved to new subnet) or client’s lease as expired
DHCPDECLINE Client to server indicating network address and in use.
DHCPRELEASE Client to server indicating network address and canceling remaining lease.
DHCPINFORM Client to server, asking only for local configuration parameters; client already has
externally configured network address.