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Cisco IOS Cookbook, 2nd Edition by Ian Brown, Kevin Dooley

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Connecting VLAN Trunks with 802.1Q

Problem

You want to connect an 802.1Q VLAN trunk directly to your router.

Solution

To connect an 802.1Q trunk to your router, use the following set of commands:

Router2#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router2(config)#interface FastEthernet1/0
Router2(config-if)#no ip address
Router2(config-if)#speed 100
Router2(config-if)#full-duplex
Router2(config-if)#exit
Router2(config)#interface FastEthernet1/0.1
Router2(config-subif)#encapsulation dot1Q 1 native
Router2(config-subif)#ip address 172.25.1.47 255.255.255.0
Router2(config-subif)#exit
Router2(config)#interface FastEthernet1/0.2
Router2(config-subif)#encapsulation dot1Q 2
Router2(config-subif)#ip address 172.25.22.4 255.255.255.0
Router2(config-subif)#exit
Router2(config)#interface FastEthernet1/0.3
Router2(config-subif)#encapsulation dot1Q 548
Router2(config-subif)#ip address 172.20.1.1 255.255.255.0
Router2(config-subif)#exit
Router2(config)#end
Router2#

Please note that to support 802.1Q features, your router must have an IOS level of at least 12.0(5)T, with the IP Plus feature set.

Discussion

The configuration for 802.1Q trunks is almost identically to the ISL configuration we discussed in Recipe 16.12. Please refer to that recipe for a more detailed discussion of trunking in general.

The most important difference between ISL and 802.1Q trunks is that 802.1Q is an IEEE open standard. If all of your switches and routers were manufactured by Cisco, you ...

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