Since the whole VPS (Virtual Private Server) thing is going so well for me, I thought that I would let my readers know about some of the steps that I took to set it up. In this episode I will be talking about updating the initially installed image and configuring the linux firewall using iptables.
Just as a side note, the VPS that I have is running Ubuntu 8.04 (Hardy Heron) so if you are using a different OS, you make have to do things a bit differently.
Update The Server
For those of you from the Windows world, this may seem to be shockingly easy. First, you need to edit the file which tells the system where to get all of the updates. I like to enable all of the sources, including universe and source code. To do this, you need to edit /etc/apt/sources.list:
sudo nano /etc/apt/sources.list
Remove the # characters in front of all the sources. When I was done, my sources.list file looked like this:
deb http://archive.ubuntu.com/ubuntu/ hardy main restricted universe
deb-src http://archive.ubuntu.com/ubuntu/ hardy main restricted universe
deb http://archive.ubuntu.com/ubuntu/ hardy-updates main restricted universe
deb-src http://archive.ubuntu.com/ubuntu/ hardy-updates main restricted universe
deb http://security.ubuntu.com/ubuntu hardy-security main restricted universe
deb-src http://security.ubuntu.com/ubuntu hardy-security main restricted universe
Now, update Ubuntu by entering these three commands one after another:
sudo aptitude –y update
sudo aptitude –y safe-upgrade
sudo aptitude –y full-upgrade
That’s all there is to it!
Configure iptables
In my opinion, this is the most important thing that you can do because it helps to restrict access to your VPS. The configuration that I am presenting here is just the basics that you should set out and you may want to tighten in down a bit afterward.
Backup
The first thing that you need to do is backup your present iptables rules:
iptables-save > /etc/iptables.up.rules
Create Filter
Next, you are going to want to create your filter. This is a set of rules that tells the firewall what you want to do with data packets that hit your network card.
First, allow all loopback (lo0) traffic and drop all traffic to 127.0.0.0/8 that doesn’t use lo0. This will allow you network services that run on your VPS to talk to other network services on your VPS:
sudo iptables -A INPUT -i lo -j ACCEPT
sudo iptables -A INPUT -i ! lo -d 127.0.0.0/8 -j REJECT
Next, accepts all established inbound connections. This means that anything that is already connected to your firewall will remain connected, even if there is a change to the rules. This is very handy to prevent you from locking yourself out of your virtual server if you accidentally disable the wrong port:
sudo iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
You want your VPS to be able to talk to anything on the Internet so you need to be enable that access:
sudo iptables -A OUTPUT -j ACCEPT
Since we are building a web server, we need to allows HTTP (port 80) and HTTPS (port 443) connections from anywhere on the Internet:
sudo iptables -A INPUT -p tcp --dport 80 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 443 -j ACCEPT
Linux servers are managed primarily via SSH. So, we need to make sure that we have an SSH port open. I decided to use a non-standard port (port 999) rather than the standard port 22:
sudo iptables -A INPUT -p tcp -m state --state NEW --dport 999 -j ACCEPT
The next line will allow you (and others) to ping your server. There is some debate as to whether or not you should allow pings but, in the end, it is really up to you:
sudo iptables -A INPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT
We will be needing to know if there is anyone out there trying to tamper with our server. So, we are going to log iptables denied calls:
sudo iptables -A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7
Since we have configured all of the ports that we want access to, we will reject all other inbound traffic that is not explicitly allowed by a policy:
sudo iptables -A INPUT -j DROP
sudo iptables -A FORWARD -j DROP
Save Rules
Now that we have created out filter/rules, we need to save it:
sudo iptables-save > /etc/iptables.up.rules
When you are finished, your /etc/iptables.up.rules file should look something like this:
# Generated by iptables-save v1.3.8 on Fri Jul 18 02:03:12 2008
*filter
:INPUT ACCEPT [15:1712]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [15:9376]
-A INPUT -i lo -j ACCEPT
-A INPUT -d 127.0.0.0/255.0.0.0 -i ! lo -j REJECT --reject-with icmp-port-unreachable
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 443 -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 999 -j ACCEPT
-A INPUT -p icmp -m icmp --icmp-type 8 -j ACCEPT
-A INPUT -m limit --limit 5/min -j LOG --log-prefix "iptables denied: " --log-level 7
-A INPUT -j DROP
-A FORWARD -j DROP
-A OUTPUT -j ACCEPT
COMMIT
# Completed on Fri Jul 18 02:03:12 2008
Configure Network to Load Rules Automatically
We need to make sure that these rules reload automatically whenever we reboot the server. Do this by editting the network interface to load the rules automatically:
sudo nano /etc/network/interfaces
Add pre-up iptables-restore < /etc/iptables.up.rules after iface lo inet loopback and then save the file.
Conclusion
With this short tutorial, we have upgraded and secured out VPS. In part 2, we are going to look at installing and configuring SSH so that we can remotely connect and manage the VPS plus we are going to add some security to our SSH sessions by changing the SSH port to 999 and setting up and using public and private keys with PuTTY in Windows.
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