I made a steam forum post already so I'm gonna copy/paste to save time.
"If I wire my computer directly to my modem I can see and connect to servers just fine. But when wired through my router I can only see some servers, and if I try to connect manually to the servers that are not showing I get "server is not responding".
I could connect to the servers while wired through my router only just a week ago and there wasn't any changes since then, to my knowledge. Both computers in my house are having this problem so I think it must be the router.
I have a D-Link DIR-625, I've tried disabling all of the firewall options, disabling QoS and UPnP, resetting it and the modem with the reset buttons, and adding steams ports. Nothing worked."
I know it's an old router but I noticed FurryNutz is still active here and seems to be very helpful so I was hoping maybe you know a solution before I have to buy a new one.