VLAN Trunk while still having a WAN port?

I want to use 802.11v over power line adapters but I need to be able to use a VDSL modem for the WAN on the router, can I somehow specify a trunk port then assign a VLAN ID to the WAN port so I can still connect to the internet with PPPOE?

I hope that makes sense!

From OpenWrt perspective you can do that.
The question is if the powerlines can relay the tagged frames.

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+1 to what @trendy said.

If your power line adapters do not explicitly list VLAN support as one of their features, it is not a good idea to run VLANs through these devices (the same recommendation is true for unmanaged switches, which operate very similarly at a functional level). You will also need smart switches connected to the all of the power line adapters to break out the VLANs properly (except for the OpenWrt device which can directly connect since it would already be VLAN aware).

So, lets assume the powerlines do work with 802.11Q

I kind of understand the concept of VLANs, but I'm not sure how to tackle what I'm attempting to do.

Lets say I have my LAN traffic tagged as 20, and the WAN for PPOE tagged as 10, would I create a new interface for PPPOE and tag it to one of the VLANs?

Start with a diagram of what you are trying to achieve, physically. Include all nodes of the power line adapters (especially if you're using more than 2) and any major network equipment such as your router, additional routers/switches/APs, etc.

Something like this?

Why not put the OpenWrt router next to the modem? If you need another wifi AP, you could add that via the power line adapter (some of them even include wifi APs built in).

On the single interface of OpenWrt you'd have lan as eth0.20 and pppoe would be using eth0.10

network.lan=interface
network.lan.proto='static'
network.lan.netmask='255.255.255.0'
network.lan.ipaddr='10.0.2.1'
network.lan.ip6assign='60'
network.lan.force_link='0'
network.lan.ip6ifaceid='::1'
network.lan.ifname='eth0.20'

network.wan=interface
network.wan.proto='pppoe'
network.wan.username='user'
network.wan.password='pass'
network.wan.peerdns='0'
network.wan.ipv6='1'
network.wan.metric='10'
network.wan.keepalive='6 10'
network.wan.ifname='eth0.10
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Location of DSL line vs optimal placement of access point.

Its more of a learning exercise than a practical use for me.

If I set tagging on ports 1 and 3, I lose access to anything behind the router when accessing it over wifi, is this expected as the wireless isnt part of a vlan group?

Pro tip - don't attempt the configuration while using the power line adapters -- if they don't work with VLANs, you will never get it to work or you may experience odd issues, even if your config is correct.

Your switch must have a trunk port (carrying both lan and wan) to the router. @trendy already described how your network would appear on eth0 of the router. The trunk must be identical on both sides -- so likely PVID blank (no default/untagged network) on the switch port that goes to the router, VID = 10, 20. The switch port that the DSL modem connects to would either be PVID = 10 and VID blank, or PVID blank and VID = 10 (depending on if the modem expects a tagged or untagged connection). Your access ports on the switch (i.e. to everything else) need to be untagged VLAN 20 -- so PVID 20, and nothing in VID. You also have to make sure your port membership is correct -- each switch manufacturer has a slightly different way of setting port VLAN memberships, but the user manual should help you with that.

Once you get it working with the router directly connected to the switch, you can try through the power line. It is, again, not advisable to use a power line adapter with VLANs unless the devices are specifically designed to handle VLANs (it would be in the documentation) -- it might work, but you could also experience odd issues.

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Ok thanks, looks like I will be scouring ebay for a cheap managed switch so I can try this out.

So I can have a PPOE interface which is just part of a VLAN group and doesn't physically exist?

You can get managed switches as inexpensive as around $20 us on amazon.

If the pppoe connection is normally untagged between your modem and router, all you are doing is using VLANs to trunk your wan and lan together. The router looks for the appropriate tags to interpret the network that each packet belongs to.

Would this do the job? https://www.amazon.co.uk/TL-SG108-Ethernet-Wall-Mount-Lifetime-Warranty/dp/B00A121WN6/ref=asc_df_B00A121WN6/

It looks like on this particular switch, you just include the port in each VLAN you set for it to become a trunk? Is that the same as you would do on openwrt?

This is not a managed switch. You need true ā€œEā€ versions.

ignore, amazon search fail.

I just remembered I have another older router that runs openwrt, so I can probably use that to test with.