Troubleshooting VLANs and Trunks Ports

By | 9th November 2015

How to troubleshoot VLANs and Trunks

Common Errors

On this page(s), we will look at common VLAN and trunking problems, which most times are caused by incorrect configurations. As I said earlier on NAT troubleshooting page, most common mistakes in troubleshooting is not your inability to use commands but the laxity in the examination of entries and configuration.


When you are configuring VLANs and trunks on a switched network, these types of configuration errors are most likely to be the causes:

Native VLAN mismatches
Trunk mode mismatches
VLANs and IP Subnets
Allowed VLANs on trunks
We will look at these likely VLAN and Trunk errors orderly. Start your troubleshooting by examining the trunks for a native VLAN mismatch and then work down the list.

Below are list of common Problems with VLANs and Trunks and their result on the network:

troubleshooting VLAN and Trunks


 Error#1  Native VLAN Mismatches

Error#2 Trunk Mode Mismatches

Error#3  Incorrect VLANs allowed on Trunks

 Error#4  Incorrect VLANs IP Subnet Configurations

 VLAN Trunking Protocol (VTP)

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