No one can establish connections from the Internet to my computers anymore because my ISP started using a symmetric NAT a couple of days ago. There wasn't any problem before, I could initiate a connection from the internet to my computers and if a server application was running on some of those computers, a connection could be established because I have port forwarding configured correctly in my router. Now, the packets can't reach my router at all.
What changes I noticed:
-The public IPv4 address which I can see on google or an IP whois site is different than the one which is set on my router's link to my ISP (my router's "WAN" link). I checked the router "WAN" interface's IP address through the router's web interface page (It's a simple home TPLink router).
-My ISP changes the source port numbers of packets that originate from my computers. For ex. a client application is bound to port number 50000 udp. My router sends out the packets with a source port number 50000. My ISP changes this source port number to an arbitrary source port number (for ex. 13418).
Problems
1) If I have a server application running on my computers I cannot send data to it from the Internet because the port isn't open on my ISP's symmetric NAT. For ex. the server listens on port 30000 on one of my computers. That port isn't open on the symmetric NAT of my ISP and if I try to send data from the Internet, the packets cannot reach my router.
2) I use an application called Voobly for gaming - Age of Empires 2 mostly. The way the connections work are: You set a listen port for the Voobly client (for example udp 16000). That port is given by Voobly to other players to establish direct connections to me. So my Voobly client sends udp packets with source port 16000, my TPLink router does NAT and keeps the udp source port 16000, but when the packets try to leave my ISP's network they change the source port to something like 13000. So I'm screwed, UDP hole punching is very hard to achieve and I am having trouble connecting even to people who live in countries next to mine.
Conclusion
I know this is a desperate attempt. I am unable to do anything about it (except maybe change ISPs). I am hoping for a miracle here. Thanks, in advance, to anyone who gives me some information.