VLAN: CONCEPT: DEFAULT vs NATIVE, CONCEPT


TOPICS

DEFAULT VLAN AND NATIVE VLAN DIFFERENCE

NATIVE VLAN CONCEPT


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DEFAULT AND NATIVE VLAN DIFFERENCE

 

Note down one thing, which some times misunderstood

In a new switch or initially,

Default VLAN=Native VLAN=VLAN 1

 

Significance of VLAN 1

Controlling traffic like CDP(Cisco Discovery Protocol: To find out connected devices), VTP, PAgP  traverse over VLAN 1

Cisco recommends to change Native VLAN from VLAN 1 to some other VLAN

VLAN 1 cannot be shut down in any case, as it carries controlling traffic

Even if we apply the command shutdown, VLAN 1 cannot be shut down

Conclusion is, In a working switch, mostly, native VLAN is not kept as VLAN 1

Then, I can say, in a working switch,

Default VLAN= VLAN 1    &     Native VLAN=Any other than VLAN 1



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NATIVE VLAN CONCEPT

 

POINTS TO BE NOTED

  • Native VLAN traffic traverse untagged, there is no tagging. If there is some traffic which is untagged, it will pass through Native VLAN only.
  • Native VLAN concept exist in case of encapsulation type 802.1Q(802.1Q supports untagged traffic, ISL do not support untagged traffic)

 

How to modify Native VLAN from VLAN 1 to any other VLAN

Switch(config-if)#switchport trunk native vlan vlan-id

 

Maximum Number of Native VLAN’s

No. of Native VLAN possible=No. of trunk ports

 

Example Scenario:                       

Why we require more than one Native VLAN in a switch?

Switches Connected   :    Network 1——–SA(F0/2)                (F0/1)SB—–Network 2

Network 1 and 2 has to be connected

At SA, we have only one Native VLAN, VLAN 20 : connected to network 1

At SB, we have only one Native VLAN, VLAN 10 : connected to network 2

Both SA and SB have different Native VLAN’s

To connect SA and SB, both should have same Native VLAN

So, either at SA and SB, One more Native VLAN is required

 

Case 1:

At SA,we create One more Native VLAN for trunk port F0/2

Switch(config)#conf t

Switch(config)#int F0/2

Switch(config-if)#switchport trunk native vlan 20

 

Case 2:

At SB,we create One more Native VLAN for trunk port F0/1

Switch(config)#conf t

Switch(config)#int F0/1

Switch(config-if)#switchport trunk native vlan 10

 

Either of above configuration will work perfect, to connect Network 1 & 2 .. !!


 

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