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I've always kept my servers behind my lan's firewall and just enabled port forwarding for whatever services I wanted to make public (ie: 80, 443, 25, 110, etc).
My new employer keeps all of their servers outside of the firewall, which makes me a little nervous but maybe I'm just being too paranoid.
So i setup a CentOS 4.3 server to run apache, dns, and postfix. In CentOS' firewall settings I checked the box to allow HTTP access (port 80 and 443), then I manually specified tcp port 53 for DNS.
Postfix is running, but it's only configured for localhost sending, so in the security window I unchecked the SMTP mail server option.
The problem is when I run a port scan on the server the port scan shows 6 open ports. 21, 25, 53 80, 110, and 443 are all "open" according to the port scanner. Is this a security threat or should I be ok? I don't have an FTP service running, so I have no idea why 21 is open. Postfix is enabled but the firewall isn't configured to allow mail connections, so I can't explain 25 and 110 (Dovecot is also disabled). 53, 80, and 443 all make sense because they are for the services I want to make public.
I guess my real question is should I try to manually configure the iptables rules or just use the default CentOS security options? I mean it is an "Enterprise" linux distro so I figured they should do things with stability and security in mind. I'd rather not go modifying things by hand.
Please let me know what you all think about my situation. Thanks!