Ccna routing and Switching Complete Study Guide

switchport trunk encapsulation dot1q

23:23:%LINEPROTO-5-UPDOWN:Line protocol on Interface GigabitEthernet0/13, 

changed state to down

23:23:%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/14, 

changed state to down

23:23:%CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on 

GigabitEthernet0/13 (392), with S2 GigabitEthernet0/13 (1).

23:23:%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/14, 

changed state to up

23:23:%LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/13, 

changed state to up

23:23:%CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on 

GigabitEthernet0/13 (392), with S2 GigabitEthernet0/13 (1).

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Troubleshooting VLAN Connectivity 

873

Okay, that’s more like it! As soon as I changed the encapsulation type on S1, DTP 

frames changed the frame-tagging method between S2 to 802.1q. Since I had already 

changed the native VLAN on port Gi0/13 on S1, the switch lets us know, via CDP, that we 

now have a native VLAN mismatch. Let’s proceed to deal with this by verifying our inter-

faces with the 

show interface trunk

 command:

S1#

sh int trunk

Port        Mode         Encapsulation  Status        Native vlan

Gi0/13      auto         802.1q         trunking      392

Gi0/14      auto         802.1q         trunking      1

 

S2#

sh int trunk

 

Port        Mode         Encapsulation  Status        Native vlan

Gi0/13      desirable    n-802.1q       trunking      1

Gi0/14      desirable    n-802.1q       trunking      1

Now notice that both links are running 802.1q and that S1 is in auto mode and S2 

is in desirable mode. And we can see a native VLAN mismatch on port Gi0/13. We can 

also see the mismatched native VLAN with the 

show interfaces 

interface switchport

 

command by looking at both sides of the link like this:

S2#