通过本实验掌握，如何在Cisco Catalyst 3550交换机来配置DHCP服务，实现对内网主机分配IP地址，网关，DNS，WINS，租期，域名等。可能你之前是在windows Server服务器或者Cisco Router 部署过DHCP,但在工程项目中，根据需求，大多是在接入层或者汇聚层多层交换机来配置的，可以同时实现DHCP Snooping等技术。
实验过程：
第一步：Catalyst 3550底层配置
Switch(config)#no ip do lo
Switch(config)#line con 0
Switch(config-line)#no exec-t
Switch(config-line)#logg syn
Switch(config-line)#host Switch_Dhcp
Switch_Dhcp(config)#int f0/1
Switch_Dhcp(config-if)#no sh
Switch_Dhcp(config-if)#spanning-tree portfast
//连接终端的接口下，开启portfast特性，跳过生成树的选举，接口立即进入转发状态
%Warning: portfast should only be enabled on ports connected to a single
host. Connecting hubs, concentrators, switches, bridges, etc... to this
interface when portfast is enabled, can cause temporary bridging loops.
Use with CAUTION
%Portfast has been configured on FastEthernet0/1 but will only
have effect when the interface is in a non-trunking mode.
Switch_Dhcp(config-if)#end
第二步: 开启DHCP服务，定义分配地址池范围及掩码，网关，DNS，域名，租期等
//全局下开启DHCP服务，该服务默认是关闭的
Switch_Dhcp(config)#service dhcp
//关闭DHCP分配冲突，日志记录消息
Switch_Dhcp(config)#no ip dhcp conflict logging
//创建DHCP地址池，名称为可以是任意字符
Switch_Dhcp(config)#ip dhcp pool cisco
//指定要通过DHCP分配的网段和掩码，还有另外一种写法（192.168.0.0 255.255.255.0）
Switch_Dhcp(dhcp-config)#network 192.168.0.0 /24
//指定分配的网关地址
Switch_Dhcp(dhcp-config)#default-router 192.168.0.1
//指定DHCP域名，域名可以为任意字符
Switch_Dhcp(dhcp-config)#domain-name www.cisco.com.cn
//指定PC通过DHCP分配到DNS地址，（这里指定的是当地电信部门的真实地址，全国各地市不一样的）
Switch_Dhcp(dhcp-config)#dns 218.30.19.40 61.134.1.4
//netbios服务器地址，可选的配置
Switch_Dhcp(dhcp-config)#netbios-name-server 192.168.0.10
//指定通过DHCP分配到地址，租期为永久
Switch_Dhcp(dhcp-config)#lease infinite
Switch_Dhcp(dhcp-config)#end
//指定不通过DHCP 地址池中分配的地址，也就是排除的地址。如果这些地址被分配给PC使用，就有可能造成网络中IP地址冲突。如：192.168.0.1 是网关地址，该地址只能是分配所有PC做网关地址，不能做IP地址使用。所以要排除。
Switch_Dhcp(config)#ip dhcp excluded-address 192.168.0.1
Switch_Dhcp(config)# ip dhcp excluded-address 192.168.0.10
第三步：查看VLAN信息，并启用SVI接口
Switch_Dhcp#show vlan brief
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Fa0/1, Fa0/2, Fa0/3, Fa0/4
Fa0/5, Fa0/6, Fa0/7, Fa0/8
Fa0/9, Fa0/10, Fa0/11, Fa0/12
Fa0/13, Fa0/15, Fa0/16, Fa0/17
Fa0/18, Fa0/19, Fa0/20, Fa0/21
Fa0/22, Fa0/23, Fa0/24, Gi0/1
Gi0/2
1002 fddi-default act/unsup
1003 token-ring-default act/unsup
1004 fddinet-default act/unsup
1005 trnet-default act/unsup
Switch_Dhcp#conf t
Enter configuration commands, one per line. End with CNTL/Z.
//进入管理VLAN1 下，启用SVI功能
Switch_Dhcp(config)#int vlan 1
//配置VLAN的地址为192.168.0.1 掩码为24位，默认情况下Cisco Catalyst交换机所有的物理接口都属于VLAN1，此地址也就是PC网关地址。
Switch_Dhcp(config-if)#ip add 192.168.0.1 255.255.255.0
Switch_Dhcp(config-if)#no sh
Switch_Dhcp(config-if)#end
Switch_Dhcp#
00:09:07: %SYS-5-CONFIG_I: Configured from console by console
Switch_Dhcp#
00:09:08: %LINK-3-UPDOWN: Interface Vlan1, changed state to up
00:09:09: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to
第四步：查看当前交换机配置文件
//验证DHCP的配置信息
Switch_Dhcp#sh run | begin ip dhcp
no ip dhcp conflict logging
ip dhcp excluded-address 192.168.0.1
ip dhcp excluded-address 192.168.0.10
!
ip dhcp pool cisco
network 192.168.0.0 255.255.255.0
default-router 192.168.0.1
domain-name www.cisco.com.cn
dns-server 218.30.19.40 61.134.1.4
netbios-name-server 192.168.0.10
lease infinite
interface Vlan1
ip address 192.168.0.1 255.255.255.0
第五步：此时将PC1的网线插入Catalyst 3550 的F0/1接口，并在PC上查看IP地址获得信息。PC上的本地连接，TCP/IP 设置为自动获得IP地址形式。
PC上查看方法：开始-运行-cmd-ipconfig/all
