Enabling vlans breaks dns

so i'm in my openwrt web config
I go to network > switch and change CPU (eth0) from untagged to tagged
i get the banner saying network lan was changed from eth0 to eth0.1
I click save and apply

my internet stops working both wired and wireless
I undo these steps and it is working again

(by stops wortking I mean everything says could not resolve address including the network diagnostics page on the openwrt web config)

any ideas whats causing this?

I am trying to add vlans for multiple wifi ssid's for roommates

You do not need VLANs to have several SSIDs, have a look to the "guest network" guide instead.

I need vlans to connect to my managed switch in my server rack in the next room to isolate my iot devices and my servers and my lan devices

ignore this topic I stated what I wanted wrong im making a new topic. moderators please delete