From my ISP I got this Sitecom WL-582 wireless router (also known as the Wireless Router 300N X2 WL-341) for my home network. By itself, it works OK, but last week I noticed that I wasn't able to connect to any Team Fortress 2 servers through Steam (Valve Software's gaming platform) on my Windows 7 (64-bit) desktop machine. The servers are hosted on random ports (some on the default 27015, but others on 27515 or 27017), so it's not 1 specific port problem. Also, I wasn't able to connect to the Relic Online service, that's used for Company of Heroes, another Steam game.
I've troubleshooted the issue by setting up port forwards, firewall rules, disabling all firewalls altogether, setting up DMZ to my machine, but all to no avail. It was only after I gave the router a factory reset (dropping all of the port forwards, firewall rules and DMZ settings again) that it worked again, but only for a while.
Today, I'm experiencing the exact same problems, while about 2 days ago after the factory reset, it did work. Whenever I connect to either of my two VPN connections, everything works fine again, so apparently the packets can reach me through the VPN/IPSec protocol, but not directly.
I'm stumped as of why this is and why this starts appearing "randomly" at some point after the factory reset. Does anybody have any clues/pointers what it might be? I'm about the throw this router out of the window, but before I do I just wanted to check if anybody might know of something I haven't checked yet.
P.S. Connecting to the servers does also work when I connect my desktop directly to my modem, so it's definitely an issue with the router and not with my ISP. Unfortunately my modem only has 1 LAN port and I have multiple devices in my network I want to have connected, so that's not a permanent solution.