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Webcast-Catalyst9k
New Member

Example of using the native VLAN (IOS)?

Hi,

Does anyone have an example of how they are using the native VLAN, other than by default? In other words, does anyone have an example or a scenario where they need to send certain traffic across the trunk untagged?

CCO says, "The IEEE committee that defined 802.1Q decided that because of backward compatibility it was desirable to support the so-called native VLAN, that is to say, a VLAN that is not associated explicitly to any tag on an 802.1Q link. This VLAN is implicitly used for all the untagged traffic received on an 802.1Q capable port."

Thank you in advance.

5 REPLIES

Re: Example of using the native VLAN (IOS)?

Hi,

one example:

Current topology:

Switch ---- PC using access port in VLAN10.

You want to add IP phone using only one port on the switch.

You can connect:

Switch --- IP phone --- PC.

You can configure the switch port as 802.1q trunk, IP phone to send 802.1q tagged frames in VLAN20, PC still sending untagged frames and with native VLAN=VLAN10 everything works fine.

Regards,

Milan

New Member

Re: Example of using the native VLAN (IOS)?

Thank you for your reply. But is there any reason why the PC needs to be sending untagged frames? I see how to configure tagged and untagged VLANs, but not clear on why you would want to send some frames, i.e. from the PC in this case, untagged.

Thanks.

Re: Example of using the native VLAN (IOS)?

1) It's always easier to leave PC configuration default (not tagging).

2) Some legacy NIC drivers might not support frame tagging.

Regards,

Milan

New Member

Re: Example of using the native VLAN (IOS)?

The following is a working example of an access switch using the native VLAN 200 and 202 for voice:

interface FastEthernet0/1

switchport trunk encapsulation dot1q

switchport trunk native vlan 200

switchport mode trunk

switchport voice vlan 202

spanning-tree portfast

-A

New Member

Re: Example of using the native VLAN (IOS)?

Thank you for your reply. But is there any reason why one VLAN needs to be sending untagged frames? I see how to configure tagged and untagged VLANs, but not clear on why you would want to send some frames untagged. Why couldn't these same frames be sent tagged?

Thanks.

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