[SOLVED] Can't open any ports, even with DMZ enabled on my modem.

Apr 22, 2020
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I am not sure what changed, but for years I was able to host a minecraft server on the port 25565, but now I am unable to open any ports to any services. My current setup is a Motorola SURFboard SBG6580 modem/router acting as a modem, and a Netgear nighthawk R6700v2 router. I have checked my firewall permissions and created permissions for inbound and outbound rules for the port 25565 as well as inbound outbound permissions for Java. I even put my SURFBoard modem/router into the DMZ by setting the DMZ to the routers IP address, and even then the IP is blocked. I have called my ISP Charter Spectrum and they have claimed that they do not block the ports I have been trying to open. I have also run the server on a different computer on the same internet and the port has remained closed. I even plugged in my desktop directly into the modem and the ports are still closed. I have quadruple checked that my IPs are correct, I have browsed multiple forums and tried multiple guides, and I am at a loss as what to do to fix this issue.
 
If the modem has a wan ip it is running as a router. When it is running in bridge mode it will only have the information about the cable channels and their strength.

You currently have the spectrum router pointed to your second router as dmz. What happens if you instead assign that IP to the server and plug the server in instead of the second router.


Your problem is either the server never gets the packet or it gets it and does not respond. With a DMZ configuration it is much more likely it is the server. Verify that the server really has a program running on the port you want to use.

After that I would consider loading wireshark on the machine. This should let you see if you are actually receiving the packet.

If you are not and you are using DMZ mode I don't know what to recommend next. Maybe set the modem to bridge mode and plug the server in directly. The server will then actually get the public ip directly. If it still does not receive the data then all that is left is the ISP is blocking it.
 
What happens if you simplify the network and put the server directly on the surfboard device and point the dmz to the server there. Since you have a second router why do you not set the surfboard to run in bridge mode. The program must actually be active on the server on that port to respond to tests.

Check the IP being assigned to the modem by the ISP on it wan port. Make sure that is a public IP. You can check sites like whatsmyip and compare. If the 2 ip addresses are not the same then you do not have a public IP.
 
Apr 22, 2020
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I do not know what bridging is to be honest, I did not set up this modem/router and router combo. I am under the impression that the SURFBoard is only acting as a modem though. When I check the WAN IP of the modem it is the same as my IP on whatsmyip, so I do have a public IP. I am not sure what the first request you have means, but I have tried portforwarding on the modem and plugging my desktop directly into the modem and running the server from there, and the port still comes up as blocked.
 
If the modem has a wan ip it is running as a router. When it is running in bridge mode it will only have the information about the cable channels and their strength.

You currently have the spectrum router pointed to your second router as dmz. What happens if you instead assign that IP to the server and plug the server in instead of the second router.


Your problem is either the server never gets the packet or it gets it and does not respond. With a DMZ configuration it is much more likely it is the server. Verify that the server really has a program running on the port you want to use.

After that I would consider loading wireshark on the machine. This should let you see if you are actually receiving the packet.

If you are not and you are using DMZ mode I don't know what to recommend next. Maybe set the modem to bridge mode and plug the server in directly. The server will then actually get the public ip directly. If it still does not receive the data then all that is left is the ISP is blocking it.
 
Apr 22, 2020
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I fixed it! What you said was correct, my modem/router was running as a router at the same time as my nighthawk router which must have prevented the port from being opened. I had no idea, I had assumed it was just acting as a modem but I was incorrect. Thanks so much! I've been trying to fix this problem for months
 

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