If I have a port A which has say VPID 200, has VLAN 200 untagged and also VLAN 150 untagged, does that mean that frames on the switch tagged 150 can reach port A, and open a connection, but port A cannot go find IPs/MACs on VLAN 150? I haven't seen this discussed in detail, but does this create 1 way VLANs in a sense?


In principle you can have only one untagged VLAN. This vlan may be called differently based on the brand but all the time it is pointing the same status. You are pointing trunk mode but there is allowed just single one native / default / untagged VLAN.

The configuration should not allow you to set more untagged VLANs and in case you could set it up that way the "last set" wins the selection so my guess is highest VLAN "win competition" about native VLAN ;-).

Available port modes:

Access mode

You can use one and only this one VLAN on the port and this VLAN is in principle untagged. This mode is used normally for connecting end nodes.

Trunk mode

This mode is when there is possible to communicate using more VLANs where one is default / native / untagged (all not tagged traffic is "assigned" to this VLAN). ALL the rest allowed VLANs have to be tagged. Based on the configuration you can allow / limit communication just for listed VLANs or you can allow all known VLANs on the device to go via the trunk port.

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  • I understand that you can only have 1 VPID, for untagged packets entering a switch port, but I haven't found (or perhaps understood) an explanation regarding multiple untagged VLANs on a port, which I have found to be possible on both TP-Link and Mikrotik switch configs.. – Bringle Apr 17 '19 at 11:52
  • It is just not possible. In case you can set it up (somehow) you just rewriting the previous set so at then end there is again just one set native VLAN (untagged). So as there cannot be multiple untagged VLANs you just can't find the explanation for that ;-). – Kamil J Apr 17 '19 at 12:39
  • In case you would not set it up (on some device it is not shown in config as it is default) the VLAN 1 is set up se default. The way how to get "other" native VLAN on the port (in one direction) could be port mirroring but it is other topic... For normal communication the situation you are asking for can't happen - one thing is what you see in configuration and other thing is how the device behave ;-). – Kamil J Apr 17 '19 at 12:45
  • In this image i.imgur.com/oj4Nukw.png you can see how a port (for example an 'access' port) can have multiple untagged VLANS, for both TP-Link and Mikrotik – Bringle Apr 17 '19 at 22:39

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