2. 租赁时间

配置文件中有与时间相关的条目。

• default-lease-time ：如果请求租用的客户端未指定持续时间，则租用保持有效的秒数。
• max-lease-time ：租约允许的最大秒数。

其他 DHCP 服务器声明

1. 静态IP地址分配的主机声明
   要向特定客户端服务器提供静态 IP 地址，请使用主机声明并包括客户端的 MAC 地址和要分配给该主机的静态 IP 地址。
   例如 ：

host server01 {
	hardware ethernet    00:14:3G:00:12:01;
	fixed-address        192.168.1.101;
	max-lease-time       84600; 
}

2. 共享网络声明
   在共享网络声明中声明共享同一物理网络的所有子网。

共享网络内但在封闭子网声明之外的参数被视为全局参数。
例如（这里的路由器参数适用于两个子网）：

shared-network [name] {
	option routers 192.168.0.254
	subnet 192.168.1.0 netmast 255.255.252.0 {
		range 192.168.1.200 192.168.1.254;
	}
	subnet 192.168.2.0 netmast 255.255.252.0 {
		range 192.168.2.200 192.168.2.254;
	}
}

3. 组声明
   使用组声明将全局参数应用于一组声明。
   共享网络、子网和主机可以组合在一起。
   例如 ：

group {
	option routers 192.168.1.254;
	host server01 {
		hardware ethernet    00:14:3G:00:12:01;
		fixed-address        192.168.1.101;
	}
	subnet 192.168.1.0 netmast 255.255.252.0 {
		range 192.168.1.200 192.168.1.254;
	}
}

1. options（选项）

信息是在请求租用时发送给每个客户端的选项行。
例如，在上面的示例配置文件中，子网掩码、广播地址、DNS 服务器 IP 地址和域名被发送到每个客户端。
每个选项声明都以分号 (;) 结束。

配置参数

3. 子网声明

子网声明包括 DHCP 服务器可以分配给客户端的 IP 地址范围。
我们可以在此处指定多个子网。
子网可以在大括号 ({}) 中声明，我们还可以为指定的子网指定其他参数。
大括号外定义的参数全局适用于所有客户端。

DHCP 主要的配置文件是 /etc/dhcp/dhcpd.conf 。
该文件用于存储 DHCP 客户端所需的网络配置信息。
在 /usr/share/doc/dhcp-[version]/dhcpd.conf.sample 中还有一个示例配置文件。

# cat /usr/share/doc/dhcp*/dhcpd.conf.sample
# dhcpd.conf
#
# Sample configuration file for ISC dhcpd
#
# option definitions common to all supported networks...
option domain-name "example.org";
option domain-name-servers ns1.example.org, ns2.example.org;
default-lease-time 600;
max-lease-time 7200;
# Use this to enble / disable dynamic dns updates globally.
#ddns-update-style none;
# If this DHCP server is the official DHCP server for the local
# network, the authoritative directive should be uncommented.
#authoritative;
# Use this to send dhcp log messages to a different log file (you also
# have to hack syslog.conf to complete the redirection).
log-facility local7;
# No service will be given on this subnet, but declaring it helps the
# DHCP server to understand the network topology.
subnet 10.152.187.0 netmask 255.255.255.0 {
}
# This is a very basic subnet declaration.
subnet 10.254.239.0 netmask 255.255.255.224 {
  range 10.254.239.10 10.254.239.20;
  option routers rtr-239-0-1.example.org, rtr-239-0-2.example.org;
}
# This declaration allows BOOTP clients to get dynamic addresses,
# which we don't really recommend.
subnet 10.254.239.32 netmask 255.255.255.224 {
  range dynamic-bootp 10.254.239.40 10.254.239.60;
  option broadcast-address 10.254.239.31;
  option routers rtr-239-32-1.example.org;
}
# A slightly different configuration for an internal subnet.
subnet 10.5.5.0 netmask 255.255.255.224 {
  range 10.5.5.26 10.5.5.30;
  option domain-name-servers ns1.internal.example.org;
  option domain-name "internal.example.org";
  option routers 10.5.5.1;
  option broadcast-address 10.5.5.31;
  default-lease-time 600;
  max-lease-time 7200;
}
# Hosts which require special configuration options can be listed in
# host statements.   If no address is specified, the address will be
# allocated dynamically (if possible), but the host-specific information
# will still come from the host declaration.
host passacaglia {
  hardware ethernet 0:0:c0:5d:bd:95;
  filename "vmunix.passacaglia";
  server-name "toccata.fugue.com";
}
# Fixed IP addresses can also be specified for hosts.   These addresses
# should not also be listed as being available for dynamic assignment.
# Hosts for which fixed IP addresses have been specified can boot using
# BOOTP or DHCP.   Hosts for which no fixed address is specified can only
# be booted with DHCP, unless there is an address range on the subnet
# to which a BOOTP client is connected which has the dynamic-bootp flag
# set.
host fantasia {
  hardware ethernet 08:00:07:26:c0:a5;
  fixed-address fantasia.fugue.com;
}
# You can declare a class of clients and then do address allocation
# based on that.   The example below shows a case where all clients
# in a certain class get addresses on the 10.17.224/24 subnet, and all
# other clients get addresses on the 10.0.29/24 subnet.
class "foo" {
  match if substring (option vendor-class-identifier, 0, 4) = "SUNW";
}
shared-network 224-29 {
  subnet 10.17.224.0 netmask 255.255.255.0 {
    option routers rtr-224.example.org;
  }
  subnet 10.0.29.0 netmask 255.255.255.0 {
    option routers rtr-29.example.org;
  }
  pool {
    allow members of "foo";
    range 10.17.224.10 10.17.224.250;
  }
  pool {
    deny members of "foo";
    range 10.0.29.10 10.0.29.230;
  }
}