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

复制代码代码如下:

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

复制代码代码如下:

//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

从以上信息可以得出，PC已经能从DHCP服务器获得IP地址等信息，实验现象成功。

第六步：查看交换机DHCP 动态绑定，以及交换机DHCP Server状态信息

复制代码代码如下:

//查看DHCP动态绑定信息，从这里可以看到PC，从DHCP地址池中的得到IP地址，以及PC的MAC地址等

Switch_Dhcp#show ip dhcp binding

IP address Client-ID/ Lease expiration Type

Hardware address

192.168.0.2 0100.16d3.249f.fd Infinite Automatic

//查看DHCP服务器工作状态

Switch_Dhcp#show ip dhcp server statistics

Memory usage 5661

Address pools 1

Database agents 0

Automatic bindings 1

Manual bindings 0

Expired bindings 0

Malformed messages 0

Message Received

BOOTREQUEST 0

DHCPDISCOVER 2

DHCPREQUEST 3

DHCPDECLINE 0

DHCPRELEASE 0

DHCPINFORM 3

Message Sent

BOOTREPLY 0

DHCPOFFER 2

DHCPACK 6

DHCPNAK 0

Switch_Dhcp#

Switch_Dhcp#clear ip dhcp binding *

第七步：使用debug 调试命令查看PC申请IP地址过程（DHCP工作过程）

在PC上：开始-运行-cmd-ipconfig /release (释放获得IP地址)

重新申请IP地址ipconfig /renew

此时查看交换机日志信息

复制代码代码如下:

Switch_Dhcp#debug ip dhcp server events

01:13:12: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/1, changed state to up

Switch_Dhcp#

01:13:13: DHCPD: DHCPDISCOVER received from client 0100.16d3.249f.fd on interface Vlan1.

Switch_Dhcp#

01:13:20: DHCPD: assigned IP address 192.168.0.3 to client 0100.16d3.249f.fd.

01:13:20: DHCPD: Sending DHCPOFFER to client 0100.16d3.249f.fd (192.168.0.3).

01:13:20: DHCPD: broadcasting BOOTREPLY to client 0016.d324.9ffd.

01:13:20: DHCPD: DHCPREQUEST received from client 0100.16d3.249f.fd.

01:13:20: DHCPD: Sending DHCPACK to client 0100.16d3.249f.fd (192.168.0.3).

01:13:20: DHCPD: broadcasting BOOTREPLY to client 0016.d324.9ffd.

Switch_Dhcp#

01:13:23: DHCPD: DHCPINFORM received from client 0100.16d3.249f.fd (192.168.0.3).

01:13:23: DHCPD: Sending DHCPACK to client 0100.16d3.249f.fd (192.168.0.3).

01:13:23: DHCPD: unicasting BOOTREPLY to client 0016.d324.9ffd (192.168.0.3).

本文出自 “王万利的博客” 博客