實驗 trunk配置
拓撲：
實驗步驟
（1） 配置各路由器相應地址,以備測試
R1(config)#interface f0/0
R1(config-if)#ip ad 192.168.0.1 255.255.255.0
R1(config-if)#no shut
R2 R3 R4 配置類似與R1
（2） 交換機配置
Switch(config)#hostname sw1
sw1(config)#vlan 2
sw1(config-vlan)#vlan 3
sw1(config-vlan)#exit
sw1(config)#interface F0/1
sw1(config-if)#switchport mode access
sw1(config-if)#switchport access vlan 2
sw1(config-if)#inter f0/2
sw1(config-if)#sw mode ac
sw1(config-if)#sw ac vlan 3
SW2配置：
Switch(config)#hostname SW2
SW2(config)#vlan 2
SW2(config-vlan)#vlan 3
SW2(config-vlan)#exit
SW2(config)#interface f0/1
SW2(config-if)#sw mod ac
SW2(config-if)#sw ac vlan 2
SW2(config-if)#interface f0/2
SW2(config-if)#sw mode ac
SW2(config-if)#sw ac vlan 3
TRUNK配置
sw1(config)#interface f0/3
sw1(config-if)#switchport trunk encapsulation dot1q
sw1(config-if)#switchport mode trunk
sw2(config)#interface f0/3
sw2(config-if)#switchport trunk encapsulation dot1q
sw2(config-if)#switchport mode trunk //接口配置成trunk
實驗測試；
R1與R3 R2與R4 都屬於同一VLAN 可以相互通信
R1>en
R1#ping 192.168.0.3 //R1 與R3 測試是否通信
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.3, timeout is 2 seconds:
!!!!!
r2#ping 192.168.0.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 66/88/94 ms
r2#
SW2#show interfaces f0/3 switchport
Name: Fa0/3
Switchport: Enabled
Administrative Mode: trunk
Operational Mode: trunk //當前接口trunk模式
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
配置 trunk allowed
sw1(config)#interface f0/3
sw1(config-if)#switchport trunk allowed vlan 2,200 //f0/3鏈路只允許vlan 2 200數據通過，則R1 R3可以通信，R2 R4不可以通信
R1#ping 192.168.0.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 65/81/94 ms
R1#
r2#ping 192.168.0.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.4, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
r2#
配置native VLAN
sw1(config)#interface f0/3
sw1(config-if)#switchport trunk native vlan 2
sw2(config)#interface f0/3
sw2(config-if)#switchport trunk native vlan 2
sw1(config)#do show inter tr
Port Mode Encapsulation Status Native vlan
Fa0/3 on 802.1q trunking 2
//可以看到trunk鏈路的native vlan 改爲2了
調試
當2個交換機native VLAN不一樣時會出現什麼後果。
sw1(config)#interface f0/3
sw1(config-if)#switchport trunk native vlan 2
sw1(config-if)#
SW2(config)#interface f0/3
SW2(config-if)#switchport TRunk native vlan 3
SW2(config-if)#
%CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on FastEthernet0/3 (2), with SW2 FastEthernet0/3 (3).
R1#ping 192.168.0.4 //測試r1與r4是否可以通信
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.0.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 78/87/94 ms
R1#
原因：S1的f0/3接口的native vlan 是 vlan 2，來自vlan 2的數據原封不動的從f0/3接口發送到sw 2上，sw2的f0/3接口的native vlan 是 vlan 3，sw2收到一個沒有經過封裝的數據幀後認爲這個幀應該是vlan 3的數據幀，發送r4，從r4返回r1也是類似的