Bricking up the doors
Ports are doorways, portals, things to enter. But because our hard work sits on one side of the entrance, openings are ruddy dangerous. Some have to be open, 24-7, because we need them for things like—duh!—serving up our sites, accessing the machine or, if we run a mail server, to enjoy all that spam. Then there are proxy ports, FTP ports, and another few besides. Actually, there are 65,535 ports or, if you must be accurate, double that. Basically, there are a lot of ports.
The problem of course is not the open door, it is the dodgy geezer with the big pockets, silent as the night, whistling through.
We cannot close all these gaping holes, such as the ones serving up our sites, and this book is concerned largely with addressing that problem. Then again, we can close almost all of them and that is a help indeed.
Ports 101
The point is to close off as many ports as possible, whether coming in or going out. So what ports do we need? Here's a summary of commonly used ports...
