What is the difference between the various interfaces (eth1, eth0, eth0.1 (lan), eth1.2 (wan, wan6)...etc)? And which one should I use in configuring the SQM QoS?
ethM -- physical Ethernet devices, typically one or two
ethM.NNNN -- VLAN sub-interfaces, used when there is only one physical interface to be able to "split" WAN from LAN in the switch, or as configured by the user
LAN -- UCI name for the bridge that typically covers an Ethernet interface to the CPU and the wireless interface(s)
WAN -- UCI name for the bridge that typically covers a different Ethernet interface to the CPU and typically used for upstream connectivity
WAN6 -- UCI name for effectively the same bridge as WAN, that allows for IPv6 configuration
I would suggest LuCI configuration of the QOS scripts if you're not comfortable with config-file editing.
1 Like
Usually in a main router you would want to run SQM on the WAN interface, the port most directly connected to the Internet. Go to the WAN network edit, physical settings tab, to see which interface is connected to WAN.
You have to use the kernel name (e.g. eth0.2) instead of the OpenWrt name (e.g. wan). This is true whether you configure with LuCi or directly in the config file.
At least from what I see, it is very likely that all packets on eth1 are on eth1.2 (a sub-interface filtering for VLAN 2), so from a functional perspective, it should make no difference.
Assuming that is correct, then purely from a clarity perspective in the way it looks in the UI, selecting "(wan, wan6)" gives a prettier picture. It's also arguably "more correct" as you are controlling the logical WAN interface.
Ok...thanks...now I will put eth1.2 (wan,wan6) on sqm interface 
When you have VLANs active on an eth interface you should always use the specific VLAN number and not refer to the 'base' interface at all.