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Vlan untagged and priority tagged doubt

Posted: Wed Oct 02, 2019 8:18 pm
by Zock
Hi everyone,

I have been using the bridge vlan method for a while configuring mikrotik switches, but i have a doubt with the Frame Types.

As you can see on Bridge>Ports>VLAN>Frame-Types there is 3 options you can play with:

1. Admit all (as it says, admits all the traffic).
2. Admit only VLAN tagged. (It doesnt allow packages without vlan tags to pass through)
3. Admit only untagged and priority tagged. (admit only packages without vlan tags AND priority tagged)

My doubt is only on the third option where it says "and priority tagged", what does that means? if it admits untagged packets and tagged ones it is not the same as "admit all" option? i dont get the difference, i dont get what priority tagged means or where i can set it in case it is a hybrid port.

Can someone explain me? thanks!

Re: Vlan untagged and priority tagged doubt  [SOLVED]

Posted: Wed Oct 02, 2019 9:14 pm
by andriys
where it says "and priority tagged", what does that means?
That means a packet with 802.1Q header that has VLAN ID field set to 0 (a reserved value that means VLAN ID is unspecified); however PCP and DEI fields are still in effect specifying priority, hence the name of the option.

Re: Vlan untagged and priority tagged doubt

Posted: Mon Oct 07, 2019 7:42 pm
by Zock
where it says "and priority tagged", what does that means?
That means a packet with 802.1Q header that has VLAN ID field set to 0 (a reserved value that means VLAN ID is unspecified); however PCP and DEI fields are still in effect specifying priority, hence the name of the option.
Thanks for your reply, i just googled PCP and DEI fields and now i get it, it is pretty well explained in the following image:

In conclusion, Admit only untagged and priority tagged means that the port will allow normal Ethernet Frames and 802.1Q tag with VID slot in 0x000 which means the Vlan 0 but it keeps the PCP and DEI default values.