31 Days Before Your CCNA Exam

92 31 Days Before Your CCNA ExamExample 23-8Trunk Configuration and Native VLAN AssignmentS1#config tEnter configuration commands, one per line. End with CNTL/Z.S1(config)#interface range fa0/1 - 5S1(config-if-range)#switchport mode trunkS1(config-if-range)#switchport trunk native vlan 99S1(config-if-range)#end%SYS-5-CONFIG_I: Configured from console by consoleS1#%CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on FastEthernet0/1(99), with S2 FastEthernet0/1 (1).%CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on FastEthernet0/3(99), with S3 FastEthernet0/3 (1).If you wait for the next round of CDP messages, you should get the error message shown inExample 23-8. Although the trunk is working between S1 and S2 and between S1 and S3, theswitches do not agree on the native VLAN. Repeat the trunking commands on S2 and S3 to correctthe native VLAN mismatch.Note The encapsulation type—dot1q or isl—might need to be configured depending onthe switch model. If so, the syntax for configuring the encapsulation type is as follows:Switch(config-if)#switchport trunk encapsulation { dot1q | isl | negotiate }The 2960 series supports only 802.1Q, so this command is not available.To verify that trunking is operational, use the commands shown in Example 23-9.Example 23-9Verifying Trunk ConfigurationS1#show interfaces trunkPort Mode Encapsulation Status Native vlanFa0/1 on 802.1q trunking 99Fa0/3 on 802.1q trunking 99Port Vlans allowed on trunkFa0/1 1-1005Fa0/3 1-1005Port Vlans allowed and active in management domainFa0/1 1,10,20,30,99,1002,1003,1004,1005Fa0/3 1,10,20,30,99,1002,1003,1004,1005Port Vlans in spanning tree forwarding state and not prunedFa0/1 1,10,20,30,99,1002,1003,1004,1005Fa0/3 1,10,20,30,99,1002,1003,1004,1005S1#show interface fa 0/1 switchportName: Fa0/1Switchport: Enabled