Hi, I just wondering can I install openwrt on old router (1 WAN+4 LAN) and make it behave as a client (STA) mode to the WAN port. Then use the other 4 LAN ports as a pure switch to serve different network?
TIA for the heads up.
You cannot directly bridge a sta mode connection to an ethernet port -- this is a limitation of the wifi standards in general.
For that part of the equation, you have the following options:
- Route -- this is the easiest method where the upstream wireless network becomes a 'wwan' for a downstream network. The downside is that this means that the ethernet connection is not on the same subnet as the upstream (this may or may not be a problem, it all depends not he specific goals/requirements of your network).
- WDS or 802.11s mesh -- this works if your upstream wifi AP is running OpenWrt. Otherwise, this isn't an option.
- relayd -- this is a bit of a hack and is not ideal, but this will work if your upstream is not running OpenWrt.
As far as making the other 4 ports into a switch for a different network, yes, that's not a problem.
thanks. will look into relayd as my upstream is not using openwrt. maybe it is easier to buy a client mode router and a switch separately.
just want to save space and electricity if possible. 
If the downstream device(s) can be on a separate subnet, routing is super easy with a sta mode upstream network. But otherwise, yes, look at relayd.
OK, will look into both slowly. the LAN has to be on same main network (wired) as upstream but the IoT in STA/client mode (TV) can be on seperate subnet.