This is a simple guide, originally written by eth0. Using these few techniques your server will attempt to stop DoS attacks (by distinguishing some legitimate connections from those that are supposed to be malicious), harden the resolf.conf file (to stop spoof DoS attacks) and fix the hosts file (removing unwanted entries).

Distinguishing those DoS attacks

In an attempt to stop DoS attacks, you can enable tcp_syncookies which will allow the server to distinguish some legitimate connections from those that are meant to be malicious. For a further explanation on tcp_syncookies, click here.

Hardening resolv.conf

You should also change the resolv.conf to make sure no spoof DoS attacks can be sent from your server, to your server. Typically, your resolv.conf file could look like this: If you see anything like the below, you need to remove the line which has the IP 127.0.0.1 in. What you need to do is make sure that you have at least your server's IP address at the top of the file. This means it will query your server. It just works like 127.0.0.1 however that IP address causes problems locally. So you could end up with something like this: Once you have done that save the file.

Removing additional hosts entries

In this file, only 2 lines should be listed (after the comments, if any). They should look something like this: If it does look like this (ignore formats such as tabs, etc) then the hosts file is correct. If it does not make sure you add a local domain with the IP address 127.0.0.1 and then your server's IP address with it's host name. If you have any more entries in that file, you can remove them.