VLAN tagging and tagging question

[yosefshai]

Hello,

I have a question about VLAN tagging on a Cisco switch.

I've learned that switches tag frames with VLAN IDs once the frame enters a Trunk port (not when it enters a VLAN port).

Now, if two computers from the same VALN and on the SAME switch talk to each other then logically there should not be any VLAN assignment on the frames (as if they were connected to a hub).

Is that correct please?

TIA

[Jon Marshall · Accepted solution]

Correct, there will be no tag in that case.

Jon

[Boyan Sotirov · Accepted solution]

In generall you're correct.

VLAN tags are used only on trunk ports. That's the idea. Simple access VLAN ports, do not and should not tag Ethernet frames.

Regarding your suggestion - it's not exactly "as a hub", it's still a switch, that means the switch will keep a MAC table for each separate VLAN. Looking at it locally - it's like you divide the switch on Layer 2 on small "switches". And the switching is done within each VLAN locally.

[Joseph W. Doherty]

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Posting

Just to muddy the waters, since VLAN edge/access ports don't normally tag frames with VLAN IDs, referencing your question about two computers "talking" to each other, it doesn't matter whether the two ports or on the same switch or even different switches; or in the same VLAN or not.

Also understand trunk ports normally tag frames, and edge/access ports don't, but an exception for the former is the "native" VLAN frames aren't tagged, and an exception for the latter, a Voice VLAN will tag frames.

[Boyan Sotirov]

Joseph,

That's a good point. I forgot about the voice VLANs, they are again in essence... trunk ports. Though specialized one.