Native VLAN

[vishalpatil86]

Hi,

WHat is native vlan concept?

Can anybody explain with example?

[mrdogantr]

Hi,

     Basically if a switch receives untagged frames on a trunkport, they are assumed to be part of the vlan that are designated on the switchport as the native vlan.

https://learningnetwork.cisco.com/thread/2217

hth

Muammer

[Latchum Naidu · Accepted solution]

Hi Vishal,

Actually with 802.1Q, a trunk link can tag frames between devices that can understood the protocol. This allows for multiple VLANs to exist on a single topology. Because 802.1Q is defined as a type of Ethernet frame, it does not require that every device on a link speaks the 802.1Q protocol. Because Ethernet is a shared media and more than two device could be connected on this media, all devices on the link must still be capable of communicating even if they do not speak the 802.1Q protocol. For this reason, 802.1Q also defines a Native VLAN. A trunk port on a switch is defined to be in a Native VLAN, and the 802.1Q trunk will not tag frames that are going out the port that came in on any port that belongs to the same VLAN that is the Native VLAN on the switch. Any Ethernet device would be capable of reading frames for the Native VLANs. The Native VLAN is important on an 802.1Q trunk link. If both sides of the link do not agree on the Native VLAN, the trunk will not operate properly.

Please click on the correct answer if this answered your question.
Regards,
Naidu.

[ranraju · Accepted solution]

Here is a discussion that helps you understand the native Vlan concept:

https://supportforums.cisco.com/thread/2070611?tstart=0&viewcondensed

However, let me give you a brief of what this native vlan is:

Consider two switches connected to eachother using a trunk link.

SwitchA --------(trunk)------- SwitchB.

The trunk port allows more than one vlan to traverse through the link. The frames crossing the trunk between the two switches, will have vlan information in its header, distinguishing itself from other vlans, meaning the frames are tagged with the vlan number. Now, on the trunk link, when you say native vlan is 5, it means that vlan 5 frames can traverse through the link without being tagged. So, by defining the native vlan as 5 on each side of the trunk you are telling the switch to send and receive frames for vlan 5 as untagged on this trunk link only. Hence by definition, if the switch sees frames coming into the switch untagged on the trunk link, it treats those frames as vlan 5 frames.

Hope this was helpful. And also answers your question.

rate the post if you find it helpful.

Regards,

ranraju