以思科三层交换机为例：
1、网络拓扑图：
2、配置命令：
1）路由器的配置：
interface FastEthernet0/0
ip address 10.66.88.222 255.255.255.0
ip nat outside
duplex auto
speed auto
interface FastEthernet0/1
ip address 192.168.1.1 255.255.255.0
ip nat inside
duplex auto
speed auto
interface Vlan1
no ip address
shutdown
ip nat
inside source list 1 interface FastEthernet0/0 overload
ip classless
ip route 192.168.2.0 255.255.255.0 192.168.1.222
ip route 192.168.3.0
255.255.255.0 192.168.1.222
access-list 1 permit 192.168.0.0 0.0.255.255
2）三层交换机的配置：
hostname L3-SW
ip dhcp pool vlan2pool
network 192.168.3.0
255.255.255.0
default-router 192.168.3.1
dns-server 202.101.172.35
ip dhcp pool vlan1pool
network 192.168.2.0 255.255.255.0
default-router 192.168.2.1
dns-server 202.101.172.35
interface
FastEthernet0/1
no switchport
ip address 192.168.1.222 255.255.255.0
duplex auto
speed auto
interface FastEthernet0/2
switchport mode
trunk
interface FastEthernet0/5
switchport mode trunk
interface
Vlan1
ip address 192.168.2.1 255.255.255.0
interface Vlan2
ip address 192.168.3.1 255.255.255.0
ip classless
ip route 0.0.0.0 0.0.0.0
192.168.1.1
