I've successfully installed OpenWRT router to my TP-LINK MR-3020 (ar11xxx). I've made a extroot for this using my flashdrive, having swap 2GB, 2GB root, and 4GB shared samba. I also tried OpenVPN solution for OpenWRT and it doesn't work under http proxy properly (maybe misconfiguration). I installed SoftEtherVPN Client and VpnCMD and it works properly and I am able to connect to my server SoftEtherVPN through HTTP Proxy.
Reason I did this because the HTTP Proxy is smart enough to filter many traffic and I want to have a transparent router box where it will route to proxy and VPN my connection automatically. Proxy send HTTP 307 Temporary Redirect everytime there are connections coming. This is not an issue with browser, but SSH with Putty is. SSH can't go through since putty not equipped to handle http redirection.
Also, in OpenWRT, I've configured 3 interface. 1 is LAN (wlan0), 1 is WAN (eth0) and 1 is Tunnel Interface (let's call it tun). If I set the default gateway to WAN (0.0.0.0/0), VPN is connected but not routed since default gateway is WAN. If I set default gateway to be VPN, WAN is replaced and VPN connection is disconnected even though I already set static route of my server VPN to route through WAN. I'm not sure why, but probably since my server VPN is not reachable from WAN except proxied. This is working properly if my server VPN is connectable from WAN (as in no proxy).
I've tried adding multiple 0.0.0.0/0 route but it does not work properly in OpenWRT. I tried to funnel all traffic to VPN and leaving it as it is in routing and still does not work (maybe misconfiguration again from my side).
Any help would be appreciated. If there's any other option beside this, I would like to try too.
Best Answer
Apparently, it was a simple as adding route to the proxy server. SoftEther VPN was contacting the proxy server and there was no route available since the proxy server reside in different subnet than the LAN/WAN. Adding proxy server route through WAN default gateway solve this issue.