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Hello I have a query I'd appreciate if you guys could help me with. I want to thoroughly TEST A FIREWALL I've built.
I've blocked off all incoming ports (INPUT) except 22 and 80 (the firewall's running apache) and it will only FORWARD port 80, 22, 25, 443. All output is accepted.
I've done some port scanning using nmap both from the outside and from within. Looks good.
Is there any other way I can test the firewall coz I've got 3 or 4 windows clients behind it and I want to make sure they aren't drawing unwanted traffic back inside. I'm only allowing incoming packets to be forwarded that are part of an established connection over ports 80, 25, 443 and 22.
So are you saying form the internal perspective. Only connections going to ports 22, 25, 80, 443. Get out onto the internet? Thats a start as that prevents some potentionly bad stuff from going on. Like IRC trojans trying to phone home, or spyware and/or legit software phoning home to some arbitrary port. Only allowing 22 and 80 into your server is good as long as you further secure those services. Maybe only allow SSH connections from specific IPs and certain users. Think about possibly chrooting that apache daemon. Someone on here can help you with that or look it up.
So I can't restrict access to ssh to certain IP addresses, right?
You might not be able to restrict ssh by IP address, but you CAN restrict ssh by user. In the sshd_conf file there is an AllowUsers line. Just list the users you want to have ssh access and it won't matter what IP address they are coming from.