三层交换：二层交换+三层转发
不同vlan之间可以通信
实例：
配置3个PC的ip地址
SW2交换机配置
Switch>enable
Switch#conf terminal
Switch(config)#hostname SW2
SW2(config)#vlan 2
SW2(config-vlan)#exit
SW2(config)#vlan 3
SW2(config-vlan)#exit
SW2(config)#interface f0/3
SW2(config-if)#switchport mode access
SW2(config-if)#switchport access vlan 2
SW2(config-if)#exit
SW2(config)#interface f0/2
SW2(config-if)#switchport mode access
SW2(config-if)#switchport access vlan 3
SW2(config-if)#exit
SW2(config)#interface f0/4
SW2(config-if)#switchport mode trunk
SW2(config-if)#end
SW2#show vlan brief
VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Fa0/1, Fa0/5, Fa0/6, Fa0/7
Fa0/8, Fa0/9, Fa0/10, Fa0/11
Fa0/12, Fa0/13, Fa0/14, Fa0/15
Fa0/16, Fa0/17, Fa0/18, Fa0/19
Fa0/20, Fa0/21, Fa0/22, Fa0/23
Fa0/24
2 VLAN0002 active Fa0/3
3 VLAN0003 active Fa0/2
F0/4不在vlan1中，所有trunk添加成功
SW3三层交换配置
Switch>enable
Switch#conf terminal
Switch(config)#hostname SW3
SW3(config)#ip routing #在三层交换上开启路由功能
SW3(config)#interface f0/1
SW3(config-if)#switchport mode trunk
SW3(config-if)#end
SW3#show interfaces f0/1 switchport
Name: Fa0/1
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: trunk
SW3#conf terminal
SW3(config)#vlan 2
SW3(config-vlan)#exit
SW3(config)#vlan 3
SW3(config-vlan)#exit
SW3(config)#interface vlan 1
SW3(config-if)#ip address 192.168.1.1 255.255.255.0
SW3(config-if)#no shutdown
SW3(config-if)#exit
SW3(config)#interface vlan 2
SW3(config-if)#ip address 192.168.2.1 255.255.255.0
SW3(config-if)#no shutdown
SW3(config-if)#exit
SW3(config)#interface vlan 3
SW3(config-if)#ip address 192.168.3.1 255.255.255.0
SW3(config-if)#no shutdown
SW3(config-if)#exit
SW3(config)#interface f0/2
SW3(config-if)#no switchport
SW3(config-if)#ip address 192.168.4.1 255.255.255.0
SW3(config-if)#no shutdown
SW3(config-if)#exit
SW3(config)#ip route 0.0.0.0 0.0.0.0 192.168.4.2
路由器上配置
Router>enable
Router#conf terminal
Router(config)#interface f0/0
Router(config-if)#ip address 192.168.4.2 255.255.255.0
Router(config-if)#no shutdown
Router(config-if)#exit
Router(config)#ip route 192.168.1.0 255.255.255.0 192.168.4.1
Router(config)#ip route 192.168.2.0 255.255.255.0 192.168.4.1
Router(config)#ip route 192.168.3.0 255.255.255.0 192.168.4.1
Router(config)#end
Router#show ip interface brief
FastEthernet0/0 192.168.4.2 YES manual up up
Router#show ip route
Gateway of last resort is not set
S 192.168.1.0/24 [1/0] via 192.168.4.1
S 192.168.2.0/24 [1/0] via 192.168.4.1
S 192.168.3.0/24 [1/0] via 192.168.4.1
C 192.168.4.0/24 is directly connected, FastEthernet0/0
在SW3三层交换上查看
SW3#show ip route
Gateway of last resort is 192.168.4.2 to network 0.0.0.0
C 192.168.1.0/24 is directly connected, Vlan1
C 192.168.2.0/24 is directly connected, Vlan2
C 192.168.3.0/24 is directly connected, Vlan3
C 192.168.4.0/24 is directly connected, FastEthernet0/2
S* 0.0.0.0/0 [1/0] via 192.168.4.2
