I have a Linksys E8450 and for starters I am trying to replace my centurylink modem and connect it to the internet using PPPoE. I have the correct credentials (because I have set it up using another router not using openWRT), but I cannot find how to setup the VLAN id to 201 and therefore this router is not able to connect. I've looked through other posts and it seems like everyone has a Network > switches menu that I don't seem to have.
The most direct way to do this is to change the wan device from wan to wan.201. Go to Network-Interfaces and edit the wan. You will need to type the new number at the bottom of the pull-down box, then press enter. (if you just click on it the setting won't take).
This model has DSA switching, so instructions you may find about configuring a switch (Network-Switch page) are not applicable.