I have to install a firewall on my server (so without X Server). It's a debian lenny. If it is possible, I want to avoid the use of
iptables. Is there a way to install/configure a firewall for a newbie ?
At first, a firewall should be the last step to secure a server. Remove all software and services which are not needed, update your system with the latest available security patches and review your config files.
Why do you want to avoid iptables?
"Because I'm a newbie" is no real excuse. A "one click everything secure" firewall doesn't exist, and if a software product uses such a slogan, its likely to be just snakeoil software.
If you are not experienced in networking basics you will have to learn this for configuring a working firewall. :-)
If you don't want to create the iptable rules yourself, you have two options:
iptables is your interface to the networking layer of the kernel. Nearly every solution for linux will depend on it.
Here is a list of GUI tools you can use to create your iptable rules:
A great book about linux servers and security is "Building Secure Servers with Linux" from O'Reilly.
Don't get discouraged and sorry for the "hard" words, but a server on the internet is not a toy and you will have some responsibility for this.
You might consider trying ufw. While it was created for Ubuntu Server, I believe that that it is also available in Debian. (UPDATE: Unfortunately, it looks like it is only available for squeeze and sid according to packages.debian.org, but it might still be worth looking at.) While I would say that you eventually want to move to writing your own iptable rules, I initially found ufw very easy to use and very easy to transition from. Here are some highlights:
This is not a "click one button and you will be secure" firewall. At the end of the day what it really does is provide an easy to use rule-creation syntax, some abstraction around
give a try at shorewall... I'm pretty happy with it and I feel it is very easy to configure whatever I need. (Including traffic shaping, NAT, DNAT and other things).