一、DHCP的工作流程
(1) DHCP服务器发现阶段。DHCP客户机向广播地址255.255.255.255发送DHCPDiscover消息。
(2) DHCP服务器响应阶段。DHCP服务器从尚未出租的IP地址池中选择一个分配给DHCP客户机，向DHCP客户机发送一个包含出租的IP地址和其他设置的DHCPoffer提供信息。
(3) IP地址选择阶段。DHCP客户机选择某个DHCP服务器提供的IP地址，以广播方式回答一个DHCPrequest请求信息.
(4) IP地址确认阶段。服务器回应包含它所提供的IP地址和其他设置的DHCPack确认信息。然后客户机将其与TCP/IP协议与网卡绑定。
(5) 客户机重新登录。再次发送前次分配的IP地址的DHCPRequest请求请求信息，DHCP服务器检查是否可以继续让客户机使用，然后发回DHCPack确认信息或者DHCPnck否认信息。如果IP已不能用，客户机需从(1)开始重新申请。
(6) 更新租约。IP地址租借期限到了，如果DHCP客户机要延长其租约，必须更新。DHCP客户机启动时和IP租约期限过一半时，都会向服务器发送更新期IP租约的信息。
二、DHCP服务器配置文件
路径在/etc/dhcp/dhcpd.conf。下面是一个配置文件的例子：
# 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; } }