Ok so I have had this problem for 2 years now, ever since Comcast and Verizon changed their modems to routers. I have reset the modem, changed the IP, and everything obvious so please don't give me a simple answer. Every time I want to make a server, be it Minecraft or Starbound, it doesn't work. Take minecraft for example, port range forward 25565, apply. I run the server and run it on 25565 and my IPv4 address, I check if the port with my external IP to see if it's open and nope. This happens with all other games I try to port forward. Static IP or not. I have a Cisco E4200, which I know is not close to a bad router and I have 50 Mb/s speed. But I also have a Verizon modem router (A modem that is also a wireless router). I do the usual hook up, Modem to router, router to computer and everything works but nobody uses the Verizon modem wireless, even though it says it's up. Can somebody please help me? I don't want to get rid of my Cisco router, it was very expensive and I'm sure it's much better than the modem. Please, I want to run a server again. It worked before I got the stupid modem.
Why won't my port forward work?
Well obviously removing the Linksys router would resolve the issue. If you really don't want to stop using it through, there may be workarounds. Do not use the Linksys router's WAN port. Be sure that it is on the same subnet as the Verizon modem (192.168.1.x for instance). Connect your computer to the Verizon router, not the Linksys. Check to see if the Verizon router has a "Bridge" mode that you can put it into. All of these may work for you.
You likely have two different firewalls using NAT (Network Address Translation)
The 1st one is the Verizon modem/router, it receives a public IP address from your ISP, then it likely has a DHCP server that assigns devices that are connected to it via wireless or hardwired private IP addresses. NAT translates the 1 public IP to multiple private IP's. The Cisco router is likely receiving a private IP for it's internet connection and translates that 1 private IP into multiple private IP's using NAT & it's own DHCP server. This is most likely why port forwarding is not working, because it would need to be done on both routers. There are different ways you can go about this. What I would do is turn off NAT/firewall and the DHCP server on the Cisco router and setup port triggering on the Verizon modem/router, start/end port 25565. This would work. But if that's not simple enough, setup port triggering on both routers, start/end port 25565, this should work as well.