do i still need a firewall

I'm studying in University of St. La Salle, i am currently
studying in advance how to setup a server.  I don't know anything about networking or linux but i want to learn, so bear with me if my question is stupid :). I'm just wondering if i still need to install a firewall to my
mini server (my computer, installed with a linux. it has an ethernet card connected to a hub with 2 modems connected to each slot. I am connected to a the internet).
When someone connects to one of the modem, do they still need to log in ? or are they automatically connected to the dialup network and to the internet? well, i want them to login first, i don't want any stranger wondering around my i still need the firewall?? in my understanding firewall are suppose to protect my modems from unauthorize requiring user to login.

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NO, If you like to learn more about firewall try support HOWTO Firewall proxy server
Whether you need a firewall or not depends on the security policy determined by your site's security administrator.  If your site doesn't have a security administrator or a documented security policy (and since you're at a university I assume it has a fairly liberal one if any), or if your site's official policy states that no firewalls are needed, then you probably don't need a firewall.  The problem is that you are creating a new network access point (through your modems onto the ethernet hub).  Most campus networks have some kind of policy about that (either for or against) and some sites (especially corporate ones) have fairly severe consequences for failing to abide by security policy (i.e. you can get fired).  Find out what kind of policy applies to you.

It is possible to configure the Linux networking subsystem to perform many of the functions of a firewall; however, if it is possible to log into the Linux server then it usually also possible to subvert the security of the Linux server (especially if the server has unnecessary software installed) and from there disable the firewall in the Linux kernel.  For this reason a separate piece of hardware (either another Linux box with all unnecessary software removed, or a dedicated commercial security product) might be required.  However, this is fairly extreme security and might be more than you'll ever need.

You might also want a firewall to prevent the Internet from having access to your machine--academic sites are well known for having less than total security and a higher number of people who know how to exploit security problems than the general population.

For any machine connected to the Internet, remember that security vulnerabilities more than six months old are routinely exploited using widely available automated searching tools.  If you have a Linux system that has not been updated in eight months or more, then you are probably vulnerable to a number of automated network attacks that grant root access to your machine to anyone who knows how to download and run software from the Internet.  See for examples.

What happens when someone connects to the modem depends on how you are set up to answer data calls.  If you're using mgetty then the /etc/mgetty+sendfax directory contains configuration files that determine how calls are handled.  mgetty can be configured to give the user the usual 'login' prompt, or it can simply hand the connection over to pppd and you can use PAP authentication within pppd itself for usernames and passwords.
misguidedAuthor Commented:
my point is do i really need one or is linux secure enough??
thanx..:) (i just want minimal security).
If you are using win95 or win98 do you have firewall on it?  
Linux is more secure than windows and if you logon on it as normal user not root then you will be fine. If you use this your computer as webserver you will want to have  firewall
If you want minimal security then you don't need a firewall.

If your system is set up correctly, the only thing a modem user will be able to do is use PPP to reach other systems.  A firewall will therefore have almost zero security impact on your system, but an impact on other systems on the same network.  If you don't consider this a problem then you just don't need a firewall.

The only thing a firewall can do is limit the modems' access to the network your machine is connected to once the modem has connected.  If you don't want to do that, then a firewall is much less useful.  They can still do cool things like IP address mapping or boring things like count the total number of network bytes sent or received though.

Note that having a firewall does not make your system "secure" -- there are dozens of ways to attack a Linux system even with a firewall:  bad (easy-to-guess) passwords, unnecessary servers, and out-of-date Linux revisions will all let intruders into your system whether you have a firewall or not.

Linux is probably secure enough for your purposes if you keep up to date with the updates on "".  Red Hat usually delivers security fixes 24 hours after they are found.

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