Ccna routing and Switching Complete Study Guide

Trunk Troubleshooting

You’ll need to troubleshoot trunk links when you lose connectivity between hosts that are 

in the same VLAN but are located on different switches. Cisco refers to this as “VLAN 

leaking.” Seems to me we are leaking VLAN 10 between switches somehow.

These are the steps we’ll take to troubleshoot VLANs:

1.

  Verify that the interface configuration is set to the correct trunk parameters.

2.

  Verify that the ports are configured correctly.

3.

  Verify the native VLAN on each switch.

And here are the commands we’ll use to perform trunk troubleshooting:

Show interfaces trunk

Show vlan

Show interfaces 

interface trunk

Show interfaces 

interface switchport

Show dtp interface 

interface

switchport mode

switchport mode dynamic

switchport trunk native vlan 

vlan

Okay, let’s get started by checking ports Gi0/13 and Gi0/14 on each switch because 

these are what the figure is showing as forming the connection between our switches. We’ll 

start with the 

show interfaces trunk

 command:

S1>