Untagged vlan frames

BaldMechanicBaldMechanic Member Posts: 8 ■□□□□□□□□□
in CCNA & CCENT
My challenge is with regards to tagged and untagged vlan frames. As I understand VLAN tagging, every vlan frame needs to be tagged in order that it is properly channeled through a trunk.

Why will there ever be an untagged frame in the first place so much so that a native vlan (the admisnistrative VLAN1 by default for that matter) will be allocated to collecting these "strays"?
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  • NetworkVeteranNetworkVeteran Member Posts: 2,338 ■■■■■■■■□□
    BaldMechanic wrote: »
    As I understand VLAN tagging, every vlan frame needs to be tagged in order that it is properly channeled through a trunk.
    There is no such requirement. A single port can support a mix of tagged and untagged frames. This mode of operation is explicitely allowed by the 802.1Q specification.
    Why will there ever be an untagged frame in the first place
    Yes. For example, imagine two switches and a PC are attached to a hub. The administrator wants to enable tagging on the switches to transport multiple VLANs, but the PC doesn't support tagging. The mixed mode of operation comes to the rescue in this case!
    so much so that a native vlan (the admisnistrative VLAN1 by default for that matter) will be allocated to collecting these "strays"?
    You're not losing a VLAN, you're simply transporting one VLAN untagged. If this is a problem for your environment, it's possible to configure that all VLANs should be tagged.
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  • YFZbluYFZblu Member Posts: 1,462 ■■■■■■■■□□
    BaldMechanic wrote: »
    My challenge is with regards to tagged and untagged vlan frames. As I understand VLAN tagging, every vlan frame needs to be tagged in order that it is properly channeled through a trunk.

    Why will there ever be an untagged frame in the first place so much so that a native vlan (the admisnistrative VLAN1 by default for that matter) will be allocated to collecting these "strays"?

    At the CCNA level, it's mostly important that you know the native VLAN isn't tagged when using 802.1Q. So like NetworkVeteran said, tagging all frames is not a requirement.
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  • NetworkVeteranNetworkVeteran Member Posts: 2,338 ■■■■■■■■□□
    YFZblu wrote: »
    At the CCNA level, it's mostly important that you know the native VLAN isn't tagged when using 802.1Q. So like NetworkVeteran said, tagging all frames is not a requirement.
    Definitely! I'd mostly expect a CCNA to know there is a native VLAN so they don't misconfigure something. (Thinking back to someone who goofed up my network before I booted them from my team!) But some context never hurts. :)
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  • BaldMechanicBaldMechanic Member Posts: 8 ■□□□□□□□□□
    Yes. For example, imagine two switches and a PC are attached to a hub. The administrator wants to enable tagging on the switches to transport multiple VLANs, but the PC doesn't support tagging. The mixed mode of operation comes to the rescue in this case!

    This clears a lot in my head, can't thank u enough. Couldn't wrap my head around why some frames go untagged.
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