DHCP：动态主机配置协议作用：自动分配IP地址到PC机工作原理：Discover消息：客户端广播发送，询问DHCP服务器的存在Offer消
息：DHCP服务器广播发送，Offer消息提供分配给客户端的IP地址、掩码、网关、DNSRequest：请求服务器确认分配该IP地
址给本地Ack：确认DHCP地址分配完成。实例配置：（DHCP服务器使用1841路由器充当）DHCP客户端：PC，自动获取IP地址
②DHCP服务器：1.足够地址下放（地址池）2.确认下放的地址：网关、DNS服务器3.租期时间：默认1天。可以修改同广播域的DHC
P配置：步骤1：Router>enRouter#conftRouter(config)#hostnameDHCP_Server
DHCP_Server(config)#interfacef0/0DHCP_Server(config-if)#ipaddre
ss192.168.10.100255.255.255.0DHCP_Server(config-if)#noshutdown
DHCP_Server(config-if)#exitDHCP_Server(config)#intf0/1DHCP_Serv
er(config-if)#ipaddress192.168.20.100255.255.255.0DHCP_Server(
config-if)#noshutdownDHCP_Server(config-if)#exit步骤2：DHCP_Server
(config)#ipdhcppool?WORDPoolnameDHCP_Server(config)#ipdhcp
pool1072(给下放地址池取一个名称)DHCP_Server(dhcp-config)#network192.168.1
0.0255.255.255.0（下放地址）DHCP_Server(dhcp-config)#endDHCP_Server#s
howrun(可查看分配的地址池)步骤3：DHCP_Server(config)#ipdhcppool1072DHCP_
Server(dhcp-config)#network192.168.20.0255.255.255.0DHCP_Server
(dhcp-config)#endDHCP_Server#showrun(可查看分配的地址池)注意：操作完步骤2和步骤3，你会
发现有步骤3下放的IP替换了步骤2的下放IP，所以，当实例图中的网络环境时，两个VLAN段，需要两个地址池，正确的配置方式为以下步
骤：步骤4：DHCP_Server(config)#noipdhcppool1072（先删除刚才配置错误的地址池）步骤5：
DHCP_Server(config)#ipdhcppool1072-vlan10(配置DHCP地址池)DHCP_Serve
r(dhcp-config)#network192.168.10.0255.255.255.0DHCP_Server(dhcp
-config)#ipdhcppool1072-vlan20(配置DHCP地址池)DHCP_Server(dhcp-conf
ig)#network192.168.20.0255.255.255.0DHCP_Server(dhcp-config)#en
dDHCP_Server#showrun(可查看分配的地址池)ipdhcppool1072-vlan10network
192.168.10.0255.255.255.0ipdhcppool1072-vlan20network192.168
.20.0255.255.255.0步骤6：DHCP_Server(config)#ipdhcppool1072-vlan
10DHCP_Server(dhcp-config)#default-router192.168.10.100（定义网关地址）D
HCP_Server(dhcp-config)#dns-server8.8.8.8(定义DNS服务器地址)DHCP_Server
(dhcp-config)#exit这条命令在真实设备上有效：DHCP_Server(config)#lease111（定义
DHCP客户端地址租期，顺序：天/时/分）步骤7：DHCP_Server(config)#ipdhcpexcluded-add
ress192.168.10.100（不自动下放分配一个IP）DHCP_Server(config)#ipdhcpexclu
ded-address192.168.10.1192.168.10.90（不自动下放分配某串连续IP的配置方法）DHCP_Se
rver(config)#end步骤8：同理，VLAN20配置方法：DHCP_Server(config)#ipdhcppoo
l1072-vlan20DHCP_Server(dhcp-config)#default-router192.168.20.1
00（网关）DHCP_Server(dhcp-config)#dns-server202.96.128.86（DNS）DHCP_
Server(dhcp-config)#exitDHCP_Server(config)#ipdhcpexcluded-addr
ess192.168.20.1192.168.20.250(不下放某段IP)跨广播域配置实例：跨广播域DHCP：广播——》单播
步骤1：删除相关的DHCP地址池信息DHCP_Server(config)#noipdhcppool1072-vlan10
DHCP_Server(config)#noipdhcppool1072-vlan20步骤2：DHCP_Server(co
nfig)#inte0/1/0DHCP_Server(config-if)#ipaddress172.16.12.1255
.255.255.0DHCP_Server(config-if)#noshutdownRouter(config)#hostna
meDHCP_Server2DHCP_Server2(config)#intf0/0DHCP_Server2(config-i
f)#ipaddress172.16.12.2255.255.255.0DHCP_Server2(config-if)#no
shutdown步骤3：DHCP_Server2(config)#ipdhcpexcluded-address192.16
8.10.100DHCP_Server2(config)#ipdhcpexcluded-address192.168.10.
1192.168.10.90DHCP_Server2(config)#ipdhcpexcluded-address192.
168.20.1192.168.20.250DHCP_Server2(config)#ipdhcppool1072-vla
n10DHCP_Server2(dhcp-config)#network192.168.10.0255.255.255.0DH
CP_Server2(dhcp-config)#default-router192.168.10.100DHCP_Server2
(dhcp-config)#dns-server8.8.8.8DHCP_Server2(dhcp-config)#ipdhcp
pool1072-vlan20DHCP_Server2(dhcp-config)#network192.168.20.02
55.255.255.0DHCP_Server2(dhcp-config)#default-router192.168.20.1
00DHCP_Server2(dhcp-config)#dns-server202.96.128.86DHCP_Server2(
dhcp-config)#end步骤4：从F0/0接口收到的DHCP广播消息，转换成单播消息到172.16.12.2DHCP_Se
rver(config)#intf0/0DHCP_Server(config-if)#iphelper-address172
.16.12.2（单播转广播）DHCP_Server(config-if)#exitDHCP_Server(config)#int
f0/1DHCP_Server(config-if)#iphelper-address172.16.12.2（单播转广播）D
HCP_Server(config-if)#exit步骤5：DHCP服务器回传消息DHCP_Server2(config)#ip
route192.168.10.0255.255.255.0172.16.12.1DHCP_Server2(config)#iproute192.168.20.0255.255.255.0172.16.12.1DHCP_Server2(config)#endDHCP_Server2#showiproutestatic（查看静态路由条目）配置：DHCP同广播域，跨广播域，VLAN的DHCP（helperaddress配置在SVI接口） |
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