I am trying to configure the WAN interface to connect to my ISP. I have taken a look at the settings of my old router and am trying to find the corresponding settings in OpenWrt.
I am using a fresh install so all other settings should be standard.
I am able to get an internet connection by connecting an LAN port from my old router to the WAN port on my OpenWrt router.
I think I need to configure the VLAN ID and VLAN priority settings but I can not find that in the WAN settings.
How can I solve this?
You can easily add the vlan subinterface if you go to Network/Interfaces/ Edit WAN interface. Then find the device field and scroll at the bottom in the custom field, where you'll enter the original interface name with dot 100. E.g if wan uses device eth0, then use eth0.100 and hit enter, then apply&save.
Depending on the model and implementation there might be some more configuration needed.
What @trendy said works if it is a DSA kernel. If you have an ath79 or other target that hasn't been converted to DSA, you will also likely need to add VLANs to the switch manually. A swconfig (not DSA) kernel can be identified by having a Switch page in the Network top menu.
If you are using the router for VLANs other than just Internet-- routing or switching phone or TV VLAN through it-- the configuration becomes more involved.