cannot access some ports even with firewall disabled

I have a server (domain controller, Win2012 R2 Foundation) and a workstation (Win10), which is joined to the domain. Firewall is turned off on both of them yet some ports are being blocked when trying to access the server from the workstation.

E.g. By way of troubleshooting, I can telnet from the workstation to the server on port 6597 but when I try telnetting via port 6607, I get a "Could not open connection to the host, on port 6607: Connect failed" error message. (seems like all ports 6598+ are blocked)

If I do a "netstat -a -n | findstr 6607" on the server, that port is "listening."

Workstation shows that it is on the Domain network in Network and Sharing Center.

There is no extra anti-virus/firewall running on either machine. The router is a simple Cisco RV-130W with no special/additional configurations.

Any suggestion what may be going on and how to open the ports?

Solution 1:

I would begin by ensuring server does not have a firewall running; it is behaving as if it has. netstat shows output from behind the firewall, so it might not be what you want. Next would be trying to access port 6607 from server itself, i.e.

1. telnet localhost 6607
2. telnet to.server.ip 6606 (they behave differently)

to verify it is not the service.

Solution 2:

I had a similar case.

What I did was uninstall my firewall and then restarted the server. I deleted all existing iptables:

sudo iptables -F

I then reinstalled my ufw firewall:

sudo apt-get install ufw

now that ufw is installed with the default open ports.

You can add other ports with the command:

sudo ufw allow portnumber/protocol

don't forget to enable your firewall:

sudo ufw enable

Note: using ufw will save you the stress of configuring your iptables which is at times stressful.