why should to define native vlan?

[Student6001186]

Hello everyone. I'm student. 

today I got some question from teacher.

he asked me that why should to define native vlan?

I try to search many web but I still don't understand.

Could someone to tell me, please? T^T

[balaji.bandi · Accepted solution]

Purpose of Native VLAN. Concept of native is to sent frames untagged on that particular vlan. All the other frames on other vlans will be tagged with particular vlan tag, once it transverses between switch to switch or switch to router.

Good example  to understand here :

https://networklessons.com/switching/802-1q-native-vlan-cisco-ios-switch

[ngkin2010 · Accepted solution]

Hi,

I think your teacher was asking why should we define a dedicated native VLAN for Native VLAN.

For example, prevent using VLAN1 (& other user's VLANs) as native VLAN on a switch's trunk link.

This is a best practice suggested by Cisco to prevent VLAN Hopping attack.

In short, if attack is on the VLAN that same as the native VLAN, then attacker could have access to all other VLAN by tagging 802.1Q header twice in its frame.

Try to search the term 'VLAN hopping' to learn more about, many blogs illustration it with pictures/animation might help you to understand it more easily.

Therefore, it's better to separate native VLAN and user VLAN in term of security.

But in the real world, I don't see many organization adopt this best practice.

[Martin L · Accepted solution]

Native vlan is vlan1 by default on every L2 switch by Cisco.  those switches also use vlan 1 by default meaning all ports belong to vlan 1 by default.  it is sort of plug and play. you turn on switch, plug in some devices and those devices will not be stopped by switch.  you can see Security risks here.

Regards, ML
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