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Community Member

What is difference between Default VLAN and Native VLAN?

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6 REPLIES

Re: What is difference between Default VLAN and Native VLAN?

Cisco switches always have VLAN 1 as the default VLAN, which is needed for many protocol communication between switches like spanning-tree protocol for instance.

You can't change or even delete the default VLAN, it is mandatory.

The native VLAN is the only VLAN which is not tagged in a trunk, in other words, native VLAN frames are transmitted unchanged.

Per default the native VLAN is VLAN 1 but you can change that:

#show interface Fa0/8 trunk

Port        Mode             Encapsulation  Status        Native vlan

Fa0/8       on               802.1q         other         1

(config-if)#switchport trunk native vlan 2

(config-if)#do show interface f0/8 trunk

Port        Mode             Encapsulation  Status        Native vlan

Fa0/8       on               802.1q         other         2

The default VLAN is still VLAN 1.

#show vlan id 1

VLAN Name Status    Ports

---- -------------------------------- --------- -------------------------------

1    default active    Fa0/8, Gi0/1

HTH

Rolf

VIP Purple

What is difference between Default VLAN and Native VLAN?

HI Pradeep,

This has already been discussed amny times:

As for answering the initial question, let's make thing simple:

  • first we'll speak about the native VLAN in terms of data frames and not management frames such as CDP,STP,VTP
  • second,  the ONLY difference between a regular VLAN and the native VLAN is that  frames from/to the native VLAN are carried untagged; this is it.

Let's get into some details now:

  • the  IEEE 802.1q TRUNKING encapsulation standard says the NATIVE VLAN  represents traffic sent and received on an interface running 802.1q    encapsulation that does not have a tag.  So altough the NATIVE VLAN  exists also on access ports, its role is relevenat only on trunk ports.
  • here  is the thing: you have 2 switches connected via a trunk port; you  create VLAN 2 on both switches; on one end of the trunk you modify the  NATIVE VLAN to be VLAN2;what will happen, just a short description?; if  the first switch (with NATIVE VLAN 1 on the trunk) receives a frame from  VLAN1 and decides it needs to send the frame on the trunk port, it will  see that the frame was issued from VLAN1 which is the NATIVE VLAN on  the trunk port it will send the frame out the trunk port UNTAGGED. Now  when switch 2 receives the frame, it sees it is untagged and it will  associate the frme with its NATIVE VLAN which is VLAN2.
  • the  NATIVE VLAN can be modified on a per-port basis or it can be "disabled",  emaning you can configure some higher-end switches to tag all frames,  so there is not NATIVE VLAN.
  • with the CDP message saying "native  VLAN mismatch" the problem is not the error messasge but the thing that  you couls have L2 loops in the network or frames hopping between VLANs  directly at L2, without a L3 device.

The error message can be seen in multiple situations:

  • CDP version mismatch; CDP version 2 carries NATIVE VLAN information while CDP version 1 does not
  • trunk with mismatched NATIVE VLANs-----my example from above
  • both ends are configured as access but on different VLANs
  • one end is configured as access on VLAN x and the other end is configured as trunk with a NATIVE VLAN different than VLAN x.

Regards

please rate if it helps.

Community Member

Re: What is difference between Default VLAN and Native VLAN?

Hi Sandeep,

Could you please give some more details on the scenario with native VLAN mismatch and the CDP warning?

How could this produce any kind of loops?

Bronze

Re: What is difference between Default VLAN and Native VLAN?

Natative VLAN is used for untagged traffic. If native VLAN differe between switches then it wont break the trunk rather CDP throws error message. for example you connect switch A to switch B, their native VLAN must be VLAN x on both switches.But if any Switch A has VAN x and Switch B has VLAN Y then you get error message. 

 

By default VLAN 1 i.e default VLAN is used as native VLAN.

Community Member

Re: What is difference between Default VLAN and Native VLAN?

Thank you for the feedback sathvik. However, this does not answer my question. My question is how a L2 loop can happen while using CDP and different native VLANs across switches. An example or maybe a graph would certainly help a lot.

Thank you

Super Bronze

Re: What is difference between Default VLAN and Native VLAN?

It doesn't, by itself, create a loop. It's just when you start interconnecting switches, unintentionally interconnecting different VLANs (whether via a trunk's native VLAN [or via access port]) you may end up creating a loop or mixing VLAN traffic you didn't intend.

What CDP does, it "flags" the VLAN mismatch.
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